Polymer

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Polymer" is a generic term used to describe a very long molecule consisting of structural units and repeating units connected by covalent chemical bonds.
A key feature that distinguishes polymers from other molecules is the repetition of many identical, similar, or complementary molecular subunits in these chains.
These subunits, the monomers, are small molecules of low to moderate molecular weight, and are linked to each other during a chemical reaction called polymerization.

Chemical compound

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A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition.
The ratio of each element is usually expressed by chemical formula.
For example, water (H2O) is a compound consisting of two hydrogen atoms bonded to an oxygen atom. The atoms within a compound can be held together by a variety of interactions, ranging from covalent bonds to electrostatic forces in ionic bonds.

Real Gases

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Deviate at least slightly from Ideal Gas Law because of two factors:
gas molecules attract one another
gas molecules occupy a finite volume
Both of these factors are neglected in the Ideal Gas law. Both increase in importance when molecules are close together (high P, low T)
van der Walls equation corrects for the attraction between molecules.nb corrects for the volume of gas moleculesvan der Walls constants are given

Kinetic Theory of Gases

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Three postulates of the Kinetic Theory
1.Gases consist of particles (atoms or molecules) in continuous, random motion.
2.Collisions between gas particles are elastic.
3.The average energy of translational motion of a gas particle is directly proportional to temperature. In addition to the postulates above, it is assumed that the volumes of the particles are negligible as compared to container volume and attractive forces between particles are neglected.
Et = average kinetic energy of translationKEavgm = mass of the particleu = average velocity of the particle
from the third postulate we can formulateT = temperature in Kelvin, c = constant which has the same value for all gases.
A.Average Speed of Gas particles (find u)c = constant = R = gas constant, NA = Avogadro's #substituting for cmass times moles (NA) equals Molar Mass (MM), substituting MM and solving for u givesusing this last equation we can solve for an individual gas particle's speed rms = root mean square, which is the average square root of the speed of the individual particles.Use R = 8.3148 , in order for the units to come out in m/s
B.Grahm's Law
effusion - the flow of gas particles through a small opening or pinhole in a container.diffusion - random motion of gas particles.formulas:if the two gases are at the same temperature then:
Experimentally usually measure the time for effusion to occur, this time is an inverse of the effusion rate (lower times-faster effusion rates)
this equation was used for the separation of U238 during WWII by effusion principles.

The Ideal Gas Law

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Variables:
V=
volume (liters, cubic decimeters, milliliters, cubic centimeters).
n=
amount in moles, n = (MM = molar mass from Periodic Table).
T=
temperature, for gases must be in Kelvin, K = oC = 273.15, usually find temperature to nearest degree, so only add 273.
P=
pressure (atmospheres, millimeters of mercury, kilopascals, torr. 1 atm = 760 mm Hg = 101.3 kPa = 760 torr = 29.92 in Hg = 14.7 lb/in2, these are all at 0 oCtorr named after Torricelli - Italian scientist, first person to accurately measure atmospheric pressure, 1640
Calculation of Gas Pressure
barometer - closed manometer, take h directly.
manometer - open manometer.Pgas = Patm + P due to h mm Hg H2O is on the atmospheric side in the h part of the equation, this will effectively give the addition or subtraction from atmospheric pressure.
Relation between variables;
PV=nRTwhere R is a true constant, it is the same for all gases and is independent of P, V, n or T.
inputting standard temperature and pressure (STP) for any gas will give the same R, Avogadro's Law - the same number of particles at the same P, T, and V.

Matter and Measurements Review

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AP ChemistryScience of chemistry dates form about 1800, chemistry is an experimental science.
1.Measured Quantities
Length
Volume
Mass
TemperatureKelvin: K= oC + 273.15Celsius: oC = K - 273.15
2.Significant Figures
significant digits: based upon the meaningful digits from the laboratory instrument, know the rules on page 13 of the textbook.
mathematics: multiplication and division addition and subtraction.
3.Conversion FactorsBased on the "bridge" between known and unknown
one step conversions
multiple step conversions
4.Types of Substances
elements: cannot be broken down into two or more simpler substances.Know symbols, location on periodic table.
compounds: contain two or more elements with fixed mass percents.sodium chloride NaCl 39.345 Na, 60.66% Cl
5.Properties of Substances:Used to identify a substance by comparing to the properties of known substances.
chemical properties
physical properties
density
solubility
specific heat: q = m ( T) (Cp)
color
6.Separation of Mixtures
distillation
chromatography

Chemical Formulas and Equations

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I.Prediction of formulas of ionic compounds
1.Charges of monatomic ions of main group elements can be predicted from position in Periodic Table.
2.Transition metal cations can have multiple charges. You must know the common transition metals.(Table 2.4 page 62)
3.Polyatomic ions; know common ions, hand out.
Names of compounds
1.Ionic Compounds: give name of cation followed by that of anion (ends in -ide). If metal forms more than one cation, as with many transition metals, then names of ions have suffixes that are related to their ionic charges: -ous refers to the lower charge: -ic refers to the higher charge.
**The IUPAC (Stock Name) system uses Roman Numerals.**
2.Names of polyatomic ions containing oxygen- some elements form several polyatomic ions with oxygen. A series of suffixes and prefixes is used to specify the relative number of oxygen atoms.
per-........-ate
greatest number of oxygen atoms
........-ate
greater
........-ite
smaller
hypo-........-ite
smallest number of oxygen atomsThe mercurous ion is an exceptional case, it requires special attention. The formula and charge for the mercurous or mercury (I) ion is Hg2+2. Note that this ion contains two mercury atoms.
3.Binary molecular compounds (two nonmetals)Indicate number of atoms of each element using greek prefixes (page 67).
PCl3
N2O5
N2H4
Acid nomenclature
Acids- Acids are molecular compounds that contain hydrogen bonded to a nonmetal to a group of atoms that behave like a nonmetal. Acids can be either binary or ternary compounds. The names of binary acids have the form Hydro-........-ic acids. The names of ternary acids use a series of prefixes and suffixes to specify the relative number of oxygen atoms in the molecule.
per-........-ic
greatest number of oxygen atoms
........-ic
greater
........-ous
smaller
hypo-........-ous
smallest number of oxygen atoms
If only two different ternary acids exist for a given nonmetal, only the suffixes -ic and -ous are used.
HClO4
perchloric acid
HClO3
chloric acid
HClO2
chlorous acid
HClO
hypochlorous acid

Significant Digit Rules

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1.The number of significant digits recorded for a measurement includes all of those digits known with certainty plus the first digit about which there is some uncertainty. The first digit in which there is some uncertainty is the first digit which is estimated
2.The only time significant digits must be considered is when dealing with measured quantities. You will only deal with two types of numbers, those which are part of a measured quantity and pure numbers. An example of a pure number is the number 2 when it indicates the diameter of a circle is twice the radius of a circle. Another pure number would be the number 5 when you say five people. Many conversion facts are also pure numbers like 5280 ft = 1 mi or 1 in = 2.54 cm. Pure numbers have infinite number of significant digits. The fact that pure numbers have an infinite number of significant digits means they will never be the number which limits the numbers of significant digits in the result of a calculation using measured quantities.
3.All digits which are not zeros are significant digits.
4.Any zeros between nonzero digits are significant
5.Any zeros which simply hold the decimal point in position are not significant digits. A simple test for this kind of zero is to write the quantity in scientific notation. If the zeros disappear they are not significant. A further description of these kinds of zeros would be either -
1"ending" zeros (for big numbers) which are to the right of any nonzero digit but to the left of the decimal point, or
2"leading" zeros (for small, decimal numbers) which are to the right of a decimal point but to the left of any nonzero digit.
6.In a number such as 56,500 a special effort must be made to indicate the place value to which the quantity was recorded in the event the zeros are significant. A line above a zero or below it indicates that the zero is significant and it is the first estimated digit or the last significant digit.
7."Trailing" zeros (for decimals) which are to the right of the decimal point and to the right of any nonzero digit are significant because they indicate the measurement has been carried to that degree of precision.
8.When adding or subtracting measurements you should first calculate the answer using all digits available. Then you should determine to which place value you should round your answer. To do this determine the estimated digit in each number used in the calculation (this would be the last significant digit in each number). Then, as you proceed from left to right, the first column in which you find an estimated digit should be the column or place value to which you should round off your answer.
9.In multiplication or division of measured quantities you should first perform all of the calculations involved. Then determine how many significant digits are in each of the quantities used in the calculations. Round off your answer so it has only as many significant digits as the quantity which contains the least number of significant digits.
10.When taking a logarithm the number of digits to the right of the decimal is equal to the number of significant digits in the number that you are taking the logarithm of.

AP Chemistry: Basic Knowledge

Author: asim /

Elements
Symbol
+Oxidation
-Oxidation
aluminum
Al
3+
barium
Ba
2+
beryllium
Be
2+
boron
B
3+
bromine
Br
-1
cadmium
Cd
calcium
Ca
2+
carbon
C
4+
-4
cesium
Cs
1+
chlorine
Cl
-1
chromium
Cr
3+
cobalt
Co
2+, 3+
copper
Cu
1+, 2+
fluorine
F
-1
gold
Au
1+
helium
He
hydrogen
H
1+
iodine
I
-1
iron
Fe
2+, 3+
lead
Pb
2+, 4+
lithium
Li
1+
magnesium
Mg
2+
manganese
Mn
mercury
Hg
neon
Ne
nickel
Ni
nitrogen
N
-3
oxygen
O
-2
phosphorus
P
-3
platiunm
Pt
potassium
K
1+
silicon
Si
silver
Ag
1+
sodium
Na
1+
strontium
Sr
2+
sulfur
S
-2
tin
Sn
2+
zinc
Zn
2+
POLYATOMIC IONS
phosphate
PO43-
ammonium
NH41+
acetate
CH3COO1-
hydroxide
OH1-
nitrate
NO31-
carbonate
CO32-
sulfate
SO42-
chlorate
ClO31-
chromate
CrO42-
dichromate
Cr2O72-
peroxide
O22-
cyanide
CN1-
permanganate
MnO41-
oxalate
C2O42-
hydrogen phosphate
HPO42-
dihydrogen phosphate
H2PO41-
thiocyanate
SCN1-
thiosulfate
S2O32-
hydrogen carbonate
HCO31-
mercury (I)
Hg22+
ACIDS
oxy-acids
acetic
CH3COOH
carbonic
H2CO3
nitric
HNO3
nitrous
HNO2
phosphoric
H3PO4
sulfuric
H2SO4
sulfurous
H2SO3
non-oxyacids
hydrochloric
HCl
hydrofluoric
HF
hydrobromic
HBr
hydroiodic
HI
hydrosulfuric
H2S
hydrocyanic
HCN

what is chemistry?

Author: asim /


Chemistry is a basic science whose central concerns are -
the structure and behaviour of atoms (elements)
the composition and properties of compounds
the reactions between substances with their accompanying energy exchange
the laws that unite these phenomena into a comprehensive system.
Chemistry is not an isolated discipline, for it merges into physics and biology. The origin of the term is obscure. Chemistry evolved from the medieval practice of alchemy. It's bases were laid by such men as Boyle, Lavoisier, Priestly, Berzelius, Avogadro, Dalton and Pasteur.

Branches Of Chemistry

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Organic Chemistry
This specific type of chemistry is concerned with elements containing carbon. Carbon is only the fourteenth most common element on earth, yet it creates the largest number of different compounds. This type of chemistry is important to the petrochemical, pharmaceutical, and textile industries. All living organisms contain at least some amount of carbon in their body. Inorganic Chemistry
This branch of chemistry deals with substances not containing carbon and that are not organic. Examples of such substances are minerals found in the earth's crust and non-living matter. There are many branches of inorganic chemistry. They include bioinorganic chemistry, nuclear science and energy, geochemistry, and synthetic inorganic chemistry, just to name a few. Physical Chemistry
This type of chemistry deals with the discovery and description of the theoretical basis of the behavior of chemical substances. This means also that it provides a basis for every bit of chemistry including organic, inorganic, and analytical. This chemistry is defined as dealing with the relations between the physical properties of substances and their chemical formations along with their changes. Biochemistry
Biochemistry is a science that is concerned with the composition and changes in the formation of living species. This type of chemistry utilizes the concepts of organic and physical chemistry to make the world of living organisms seem much clearer. Some people also consider biochemsitry as physiological chemistry and biological chemistry. The scientists that study biochemistry are called biochemists. They study such things as the properties of biological molecules, including proteins, lipids, carbohydrates, and nucleic acids. Other topics they focus on are the chemical regulation of metabolism, the chemistry of vitamins, and biological oxidation. Analytical Chemistry
This kind of chemistry deals mostly with the composition of substances.
All these branches of chemistry must deal with each other one way or another. If they didn't work in unison it would be impossible for these chemistries to perform the functions we need for experiments. For example you wouldn't be able measure the change of an organic substance without knowing how to use analytical chemistry.

Molecular Formula

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A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions. For molecular compounds it is also known as the molecular formula, and identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol (although 19th-century books often used superscripts). For ionic compounds and other non-molecular substances, the subscripts indicate the ratio of elements in the empirical formula.

Molecular mass

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The molecular mass (abbreviated M) of a substance, frequently referred by the older term molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u[1] (equal to 1/12 the mass of one isotope of carbon-12[2]). This is distinct from the relative molecular mass of a molecule, which is the ratio of the mass of that molecule to 1/12 of the mass of carbon 12 and is a dimensionless number. Relative molecular mass is abbreviated to Mr.
Molecular mass differs from more common measurements of the mass of chemicals, such as molar mass, by taking into account the isotopic composition of a molecule rather than the average isotopic distribution of many molecules. As a result molecular mass is a more precise number than molar mass; however it is more accurate to use molar mass on bulk samples. This means that molar mass is appropriate most of the time except when dealing with single molecules.

Atomic mass

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The atomic mass (ma) is the mass of an atom, most often expressed in unified atomic mass units.[1] The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom (when the atom is motionless). The atomic mass is sometimes incorrectly used as a synonym of relative atomic mass, average atomic mass and atomic weight; however, these differ subtly from the atomic mass. The atomic mass is defined as the mass of an atom, which can only be one isotope at a time and is not an abundance-weighted average. In the case of many elements that have one dominant isotope the actual numerical similarity/difference between the atomic mass of the most common isotope and the relative atomic mass or standard atomic weights can be very small such that it does not affect most bulk calculations-- but such an error can be critical when considering individual atoms. For elements with more than one common isotope the difference even to the most common atomic mass can be half a mass unit or more (e.g. chlorine). The atomic mass of an uncommon isotope can same/differ from the relative atomic mass or standard atomic weight by several mass units.

Atomic number

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In chemistry and physics, the atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element. In an atom of neutral charge, atomic number is equal to the number of electrons.
The atomic number, Z, should not be confused with the mass number, A, which is the total number of protons and neutrons in the nucleus of an atom. The number of neutrons, N, is known as the neutron number of the atom; thus, A = Z + N. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes), the atomic mass of an atom is roughly equal to A.
Atoms having the same atomic number Z but different neutron number N, and hence different atomic masses, are known as isotopes. Most naturally occurring elements exist as a mixture of isotopes, and the average atomic mass of this mixture determines the element's atomic weight. The current standard for the atomic mass unit (amu), also termed the dalton (Da) is defined to be exactly 1/12th of the mass of a free (unbound) neutral 12C atom in its lowest-energy, or "ground" state.[1] In SI units, 1 Da = 1.660538782(83)×10−27 kg.

Discovery of the Neutron (1932)

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Until 1932, the atom was known to consist of a positively charged nucleus surrounded by enough negatively charged electrons to make the atom electrically neutral. Most of the atom was empty space, with its mass concentrated in a tiny nucleus. The nucleus was thought to contain both protons and electrons because the proton (otherwise known as the hydrogen ion, H+) was the lightest known nucleus and because electrons were emitted by the nucleus in beta decay. In addition to the beta particles, certain radioactive nuclei emitted positively charged alpha particles and neutral gamma radiation. The symbols for these emissions are b - or –1e0, a 2+ or 24He2+, and 00g .
Twelve years earlier, Lord Ernest Rutherford, a pioneer in atomic structure, had postulated the existence of a neutral particle, with the approximate mass of a proton, that could result from the capture of an electron by a proton. This postulation stimulated a search for the particle. However, its electrical neutrality complicated the search because almost all experimental techniques of this period measured charged particles.
In 1928, a German physicist, Walter Bothe, and his student, Herbert Becker, took the initial step in the search. They bombarded beryllium with alpha particles emitted from polonium and found that it gave off a penetrating, electrically neutral radiation, which they interpreted to be high-energy gamma photons.

Discovery of Proton

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Prior to the late nineteenth and early twentieth centuries, scientists believed that atoms were indivisible. Work by many scientists led to the nuclear model of the atom, in which protons, neutrons, and electrons make up individual atoms. Protons and neutrons are found in the nucleus, while electrons are found in a much greater volume around the nucleus. The nucleus represents less than 1% of the atom's total volume.
The proton's mass and charge have both been determined. The mass is 1.673 × 10-24 g. The charge of a proton is positive, and is assigned a value of +1. The electron has a –1 charge, and is about 2,000 times lighter than a proton. In neutral atoms, the number of protons and electrons are equal.
The number of protons (also referred to as the atomic number) determines the chemical identity of an atom. Each element in the periodic table has a unique number of protons in its nucleus. The chemical behavior of individual elements largely depends, however, on the electrons in that element. Chemical reactions involve changes in the arrangements of electrons, not in the number of protons or neutrons.
The processes involving changes in the number of protons are referred to as nuclear reactions. In essence, a nuclear reaction is the transformation of one element into another. Certain elements—both natural and artificially made—are by their nature unstable, and spontaneously break down into lighter elements, releasing energy in the process. This process is referred to as radioactivity. Nuclear power is generated by just such a process.Read more: http://science.jrank.org/pages/5551/Proton-Discovery-properties.html#ixzz0J376HZXT&C

Discovery of Electron

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ne hundred years ago, amidst glowing glass tubes and the hum of electricity, the British physicist J.J. Thomson was venturing into the interior of the atom. At the Cavendish Laboratory at Cambridge University, Thomson was experimenting with currents of electricity inside empty glass tubes. He was investigating a long-standing puzzle known as "cathode rays." His experiments prompted him to make a bold proposal: these mysterious rays are streams of particles much smaller than atoms, they are in fact minuscule pieces of atoms. He called these particles "corpuscles," and suggested that they might make up all of the matter in atoms. It was startling to imagine a particle residing inside the atom--most people thought that the atom was indivisible, the most fundamental unit of matter.

Radioactive decay

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Every element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing the nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm.[77]
The most common forms of radioactive decay are:[78][79]
Alpha decay is caused when the nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. The result of the emission is a new element with a lower atomic number.
Beta decay is regulated by the weak force, and results from a transformation of a neutron into a proton, or a proton into a neutron. The first is accompanied by the emission of an electron and an antineutrino, while the second causes the emission of a positron and a neutrino. The electron or positron emissions are called beta particles. Beta decay either increases or decreases the atomic number of the nucleus by one.
Gamma decay results from a change in the energy level of the nucleus to a lower state, resulting in the emission of electromagnetic radiation. This can occur following the emission of an alpha or a beta particle from radioactive decay.

Electron cloud

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The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed in order for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations.
Electrons, like other particles, have properties of both a particle and a wave. The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing wave—a wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital, a mathematical function that characterises the probability that an electron will appear to be at a particular location when its position is measured.[55] Only a discrete (or quantized) set of these orbitals exist around the nucleus, as other possible wave patterns will rapidly decay into a more stable form.[56] Orbitals can have one or more ring or node structures, and they differ from each other in size, shape and orientation.[57]

Nucleus

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All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to fm, where A is the total number of nucleons.[46] This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other.[47]

mass spectrometer

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The development of the mass spectrometer allowed the exact mass of atoms to be measured. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom's mass to its charge. The chemist Francis William Aston used this instrument to demonstrate that isotopes had different masses. The mass of these isotopes varied by integer amounts, called the whole number rule.[31] The explanation for these different atomic isotopes awaited the discovery of the neutron, a neutral-charged particle with a mass similar to the proton, by the physicist James Chadwick in 1932. Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus.[32]

Atom

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The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determine the isotope of the element.

chain reaction

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1 (in chemistry) a reaction that proceeds through one or more reactive intermediates; one of the required reactive intermediates (usually free radicals) is formed in each step of the reaction. Examples include the polymerization of organic monomers into plastics or in the free radical halogenation of hydrocarbons.
2 (in physics) a reaction that perpetuates itself by the proliferating fission of nuclei and the release of atomic particles that cause more nuclear fissions.

Molecular Mass Calculations

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The formula for carbon monoxide is composed of one atom of carbon and one atom of oxygen
Atomic mass carbon = 12.01 (from the Periodic Table) Atomic mass of oxygen = 16.00 (from the Periodic Table)
Molecular Mass (MM) for cabon monoxide = atomic mass carbon + atomic mass oxygen
Molecular mass (MM) = 12.01 + 16.00 = 28.01 g/mole

Formula Mass (Formula Weight)

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The relative formula mass, FM, (formula weight, FW) of a compound is the sum of the atomic masses (atomic weights) of the atomic species as given in the formula of the compound.
Formula Mass (Formula Weight) is a more general term that can be applied to compounds that are not composed of molecules, such as ionic compounds.
In practice, the terms, molecular mass, molecular weight, formula mass and formula weight are used interchangeably by Chemists.

Formula Mass (Formula Weight)

Author: asim /


The relative formula mass, FM, (formula weight, FW) of a compound is the sum of the atomic masses (atomic weights) of the atomic species as given in the formula of the compound.
Formula Mass (Formula Weight) is a more general term that can be applied to compounds that are not composed of molecules, such as ionic compounds.
In practice, the terms, molecular mass, molecular weight, formula mass and formula weight are used interchangeably by Chemists.

Molecular Mass (Molecular Weight)

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In theory, the relative molecular mass or molecular weight of a compound is the mass of a molecule of the compound relative to the mass of a carbon atom taken as exactly 12.
In practice, the molecular mass, MM, (molecular weight, MW) of a compound is the sum of the atomic masses (atomic weights) of the atomic species as given in the molecular formula.
In theory we can only refer to the Molecular Mass or Molecular Weight of a covalent compound since only covalent compounds are composed of molecules.

Molecules of Compounds

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A molecule of a compound consists of two or more atoms of different elements joined together in a fixed ratio.

Examples: CuSO4 contains Cu - 1 atom, S - 1 atom, O - 4 atoms

A chemical formula represents the composition of a molecule of the substance in terms of the symbol of the elements present in the molecule. It is also called molecular formula.

Microscale Gas Chemistry Experiments with Oxygen

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THESE THREE MEN, Carl Scheele (Sweden), Joseph Priestley (England), and Antoine Lavoisier (France) all claimed credit for the discovery of the element that we now call oxygen. Carl Scheele discovered fire air [oxygen] sometime before 1773. He produced the gas several ways. In one method, he reacted (using modern names) nitric acid with potash (KOH and/or K2CO3) which formed KNO3. Distilling the residue with sulfuric acid produced both NO2 and O2. The former was absorbed by limewater (saturated Ca(OH)2), leaving fire air. He also obtained fire air from strongly heating HgO and MnO2 and by heating silver carbonate or mercuric carbonate and then absorbing the CO2 by alkali (KOH):
AgCO3(s) Ag(s) + CO2(g) + O2(g)
On August 1, 1774 Joseph Priestley first prepared oxygen by directing the sun's light with a 12-inch diameter burning lens onto a sample of red mercurius calcinatus per se (now HgO). Thus, Priestley independently had discovered oxygen which he called dephlogisticated air. His explanation of the reaction using was:
mercurius calcinatus per se + heat yields quicksilver + dephlogisticated air
Today, we would describe the same reaction as follows:
HgO(s) Hg(l) + O2(g)

Uses of Carbon dioxide

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Carbon dioxide is used by the food industry, the oil industry, and the chemical industry.[10] It is used in many consumer products that require pressurized gas because it is inexpensive and nonflammable, and because it undergoes a phase transition from gas to liquid at room temperature at an attainable pressure of approximately 60 bar (870 psi, 59 atm), allowing far more carbon dioxide to fit in a given container than otherwise would. Life jackets often contain canisters of pressured carbon dioxide for quick inflation. Aluminum capsules are also sold as supplies of compressed gas for airguns, paintball markers, for inflating bicycle tires, and for making seltzer. Rapid vaporization of liquid carbon dioxide is used for blasting in coal mines. High concentrations of carbon dioxide can also be used to kill pests, such as the Common Clothes Moth.

History of human understanding

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Carbon dioxide was one of the first gases to be described as a substance distinct from air. In the seventeenth century, the Flemish chemist Jan Baptist van Helmont observed that when he burned charcoal in a closed vessel, the mass of the resulting ash was much less than that of the original charcoal. His interpretation was that the rest of the charcoal had been transmuted into an invisible substance he termed a "gas" or "wild spirit" (spiritus sylvestre).
The properties of carbon dioxide were studied more thoroughly in the 1750s by the Scottish physician Joseph Black. He found that limestone (calcium carbonate) could be heated or treated with acids to yield a gas he called "fixed air." He observed that the fixed air was denser than air and did not support either flame or animal life. Black also found that when bubbled through an aqueous solution of lime (calcium hydroxide), it would precipitate calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation. In 1772, English chemist Joseph Priestley published a paper entitled Impregnating Water with Fixed Air in which he described a process of dripping sulfuric acid (or oil of vitriol as Priestley knew it) on chalk in order to produce carbon dioxide, and forcing the gas to dissolve by agitating a bowl of water in contact with the gas.[7]
Carbon dioxide was first liquefied (at elevated pressures) in 1823 by Humphry Davy and Michael Faraday.[8] The earliest description of solid carbon dioxide was given by Charles Thilorier, who in 1834 opened a pressurized container of liquid carbon dioxide, only to find that the cooling produced by the rapid evaporation of the liquid yielded a "snow" of solid CO2.[9]

Properties of carbon dioxide

Author: asim /

There are several physical and chemical properties, which belong to carbon dioxide.Here we will sum them up in a table.
Property
Value
Molecular weight
44.01
Specific gravity
1.53 at 21 oC
Critical density
468 kg/m3
Concentration in air
370,3 * 107 ppm
Stability
High
Liquid
Pressure < 415.8 kPa
Solid
Temperature < -78 oC
Henry constant for solubility
298.15 mol/ kg * bar
Water solubility
0.9 vol/vol at 20 oC

What is carbon dioxide and how is it discovered?

Author: asim /


Joseph Black, a Scottish chemist and physician, first identified carbon dioxide in the 1750s. At room temperatures (20-25 oC), carbon dioxide is an odourless, colourless gas, which is faintly acidic and non-flammable.Carbon dioxide is a molecule with the molecular formula CO2. The linear molecule consists of a carbon atom that is doubly bonded to two oxygen atoms, O=C=O.Although carbon dioxide mainly consists in the gaseous form, it also has a solid and a liquid form. It can only be solid when temperatures are below -78 oC. Liquid carbon dioxide mainly exists when carbon dioxide is dissolved in water. Carbon dioxide is only water-soluble, when pressure is maintained. After pressure drops the CO2 gas will try to escape to air. This event is characterised by the CO2 bubbles forming into water.

Energy - Absorbed or Released

Author: asim /


Another sign of a chemical change is the release or gain of energy by an object. Many substances absorb energy to undergo a chemical change. Energy is absorbed during chemical changes involved in cooking, like baking a cake.

Chemical Changes

Author: asim /


Chemical Changes are also called Chemical Reactions. Chemical reactions involve combining different substances. The chemical reaction produces a new substance with new and different physical and chemical properties.
Matter is never destroyed or created in chemical reactions. The particles of one substance are rearranged to form a new substance. The same number of particles that exist before the reaction exist after the reaction.

Chemical vs Physical Change

Author: asim /


The most important thing for your to remember is that in a physical change the composition of a substance does not change and in a chemical change the composition of a substance does change.

Atoms Around Us

Author: asim /


If you want to have a language, you will need an alphabet. If you want to build proteins, you will need amino acids. Other examples in chemistry are not any different. If you want to build molecules, you will need elements. Each element is a little bit different from the rest. Those elements are the alphabet to the language of molecules. Why are we talking about elements? This is the section on atoms. Let's stretch the idea a bit. If you read a book, you will read a language. Letters make up that language. But what makes those letters possible? Ummm... Ink? Yes! You need ink to crate the letters. And for each letter, it is the same type of ink. Confused? Don't be. Elements are like those letters. They have something in common. That's where atoms come in. All elements are made of atoms. While the atoms may have different weights and organization, they are all built in the same way. Electrons, protons, and neutrons make the universe go. If you want to do a little more thinking, start with particles of matter. Matter, the stuff around us, is used to create atoms. Atoms are used to create the elements. Elements are used to create molecules. It just goes on. Everything you see is built by using something else. You could start really small...- Particles of matter- Atoms- Elements- Molecules- Macromolecules- Cell organelles- Cells- Tissues- Organs- Systems- Organisms- Populations- Ecosystems- Biospheres- Planets- Planetary Systems with Stars- Galaxies- The Universe.And finish really big. Wow. All of that is possible because of atoms.

The List of Elements

Author: asim /

We've got 18 to choose from. From the launch of the site we've been asked, "Why start with 18?" The rules for the first 18 elements are very straight-forward. (1) Electrons fit nicely into three shells.(2) These elements make up most of the matter in the universe.(3) It's a lot easier to remember facts about 18 elements than over 100 elements.
Element 1: HydrogenElement 2: HeliumElement 3: LithiumElement 4: BerylliumElement 5: BoronElement 6: CarbonElement 7: NitrogenElement 8: OxygenElement 9: Fluorine
Element 10: NeonElement 11: SodiumElement 12: MagnesiumElement 13: AluminumElement 14: SiliconElement 15: PhosphorusElement 16: SulfurElement 17: ChlorineElement 18: ArgonWho are we kidding? We teased you with only 18 elements for many years. We've added the next 18 elements from the fourth period. You need to remember that this is the first row with transition elements. Those transition metals have electron configurations that are a little different from the first 18. Make sure you understand the first 18 before you move on to this set.
Element 19: PotassiumElement 20: CalciumElement 21: ScandiumElement 22: TitaniumElement 23: VanadiumElement 24: ChromiumElement 25: ManganeseElement 26: IronElement 27: Cobalt
Element 28: NickelElement 29: CopperElement 30: ZincElement 31: GaliumElement 32: GermaniumElement 33: ArsenicElement 34: SeleniumElement 35: BromineElement 36: Krypton

The Same Everywhere

Author: asim /


As far as we know, there are only so many basic elements. Up to this point in time we have discovered/created over 100. While there may be more out there to discover, the basic elements remain the same. Iron (Fe) atoms found on Earth are identical to iron atoms found on meteorites. The iron atoms on Mars that make the soil red are the same too. The point is... With the tools you learn here, you can explore and understand the universe. You will never stop discovering new reactions and compounds, but the elements will remain the same.

Periodic Table and the Elements

Author: asim /


Now we're getting to the heart and soul of the way your universe works. Elements are the building blocks of all matter. We talked about quarks in the atoms section. They are smaller than the atoms of an element, but only when they group with other quarks do they form atoms that have recognizable traits. Some quarks combine to make an oxygen (O) atom. Other quarks can combine to form a nitrogen (N) atom. It's the atoms that are different and unique, even though they are made of the same pieces.

Changing States of Matter

Author: asim /


Elements and compounds can move from one physical state to another and not change. Oxygen (O2) as a gas still has the same properties as liquid oxygen. The liquid state is colder and denser but the molecules are still the same. Water is another example. The compound water is made up of two hydrogen (H) atoms and one oxygen (O) atom. It has the same molecular structure whether it is a gas, liquid, or solid. Although its physical state may change, its chemical state remains the same. So you ask, "What is a chemical state?" If the formula of water were to change, that would be a chemical change. If you added another oxygen atom, you would make hydrogen peroxide (H2O2). Its molecules would not be water anymore. Changing states of matter is about changing densities, pressures, temperatures, and other physical properties. The basic chemical structure does not change.

Matter is the Stuff Around You

Author: asim /


Matter is everything around you. Matter is anything made of atoms and molecules. Matter is anything that has a mass. Matter is also related to light and electromagnetic radiation. Even though matter can be found all over the universe, you usually find it in just a few forms. As of 1995, scientists have identified five states of matter. They may discover one more by the time you get old. You should know about solids, liquids, gases, plasmas, and a new one called Bose-Einstein condensates. The first four have been around a long time. The scientists who worked with the Bose-Einstein condensate received a Nobel Prize for their work in 1995. But what makes a state of matter? It's about the physical state of molecules and atoms.

Chemical Reactions

Author: asim /


Let's start with the idea of a reaction. In chemistry, a reaction happens when two or more molecules interact and something happens. That's it. What molecules are they? How do they interact? What happens? Those are all the possibilities in reactions. The possibilities are infinite. There are a few key points you should know about chemical reactions.
Key Points1. A chemical change must occur. You start with one compound and turn it into another. That's an example of a chemical change. A steel garbage can rusting is a chemical reaction. That rusting happens because the iron (Fe) in the metal combines with oxygen (O2) in the atmosphere. When a refrigerator or air conditioner cools the air, there is no reaction. That change in temperature is a physical change. Nevertheless, a chemical reaction can happen inside of the air conditioner. 2. A reaction could include ions, molecules, or pure atoms. We said molecules in the previous paragraph, but a reaction can happen with anything, just as long as a chemical change occurs (not a physical one). If you put pure hydrogen gas (H2) and pure oxygen gas in a room, they can be involved in a reaction. The slow rate of reaction will have the atoms bonding to form water very slowly. If you were to add a spark, those gases would create a reaction that would result in a huge explosion. Chemists would call that spark a catalyst. 3. Single reactions often happen as part of a larger series of reactions. Take something as simple as moving your arm. The contraction of that muscle requires sugars for energy. Those sugars need to be metabolized. You'll find that proteins need to move in a certain way to make the muscle contract. A whole series (hundreds actually) of different reactions are needed to make that simple movement happen.