Element: the simplest chemical substance that can exist, comprised of atoms with the same number of protons (and thus electrons).
Compound: a substance formed by the chemical combination of two or more elements. A mixture of elements (e.g. nitrogen and oxygen in the air) is not a compound because those elements are not chemically combined.
Atom: the smallest part of an element that can exist. Consists of a nucleus of neutrons and protons, which is orbited by electrons in fixed energy levels (shells). Atoms are uncharged because they have the same numbers of protons and electrons.
Protons: subatomic particles, charge +1, relative mass 1.
Neutrons: subatomic particles, charge 0, relative mass 1.
Electrons: subatomic particles, charge -1, relative mass 1/1836.
Atomic Number: The number of protons in the nucleus of an atom of a particular element.
Molecule: the smallest part of most elements and all compounds that exists alone under ordinary conditions. Molecules are uncharged because they have the same numbers of protons and electrons.
Isotopes: Atoms of the same element (same atomic number), which have different numbers of neutrons (different atomic mass). Hydrogen has 3 isotopes- regular hydrogen has 1 proton in its nucleus, deuterium has one proton and one neutron and tritium has one proton and 2 neutrons.
Mole: the amount of substance that contains as many specified entities as there are in 12 g of carbon-12, i.e. the amount of substance that contains 6.02×1023 entities. 6.02×1023 is known as Avogadro’s number or the Avogadro constant.
Empirical formula: the simplest whole number ratio of the atoms of different elements in a compound.
Molecular formula: the actual number of atoms of different elements in one molecule of a compound.
Ion: A charged particle. Ions can be monatomic (charged atom) or polyatomic (charged molecule). Positively charged ions are called cations; negatively charged ions are called anions.
Species: A generic term used to describe any particle/entity- molecule, atom, ion, etc. A pure chemical species contains identical entities.
Atom - Timeline
1704 | Isaac Newton | Proposed a mechanical universe with small solid masses in motion. |
1803 | John Dalton | Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. |
1832 | Michael Faraday | Studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. Faraday himself was not a proponent of atomism. |
1873 | James Clerk Maxwell | Proposed electric and magnetic fields filled the void. |
1879 | Sir William Crookes | Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. |
1886 | E. Goldstein | Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron. |
1894 | G.J. Stoney | Proposed that electricity was made of discrete negative particles he called electrons ". (Link to info on electrons) |
1895 | Wilhelm Roentgen | Using a CRT he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays". |
1896 | Henri Becquerel | While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays. |
1897 | J.J. Thomson | Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram. |
1898 | Rutherford | Studied radiations emitted from uranium and thorium and named them alpha and beta. |
1898 | Marie Sklodowska Curie | Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium. |
1900 | Max Planck | used the idea of quanta (discrete units of energy) to explain hot glowing matter. |
1905 | Albert Einstein | Published the famous equation E=mc 2 |
1909 | R.A. Millikan | Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. |
1911 | Ernest Rutherford | Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm)gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus. |
1922 | Niels Bohr | Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. |
1923 | de Broglie | Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein. |
1927 | Heisenberg | Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle. |
1930 | Schrodinger | Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. |
1932 | James Chadwick | Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron. |
1942 | Enrico Fermi | Conducted the first controlled chain reaction releasing energy from the atoms nucleus. |
Atomic Number |
Symbol |
Name |
1 |
H |
Hydrogen |
2 |
He |
Helium |
3 |
Li |
Lithium |
4 |
Be |
Beryllium |
5 |
B |
Boron |
6 |
C |
Carbon |
7 |
N |
Nitrogen |
8 |
O |
Oxygen |
9 |
F |
Fluorine |
10 |
Ne |
Neon |
11 |
Na |
Sodium |
12 |
Mg |
Magnesium |
13 |
Al |
Aluminium |
14 |
Si |
Silicon |
15 |
P |
Phosphorus |
16 |
S |
Sulfur |
17 |
Cl |
Chlorine |
18 |
Ar |
Argon |
19 |
K |
Potassium |
20 |
Ca |
Calcium |
21 |
Sc |
Scandium |
22 |
Ti |
Titanium |
23 |
V |
Vanadium |
24 |
Cr |
Chromium |
25 |
Mn |
Manganese |
26 |
Fe |
Iron |
27 |
Co |
Cobalt |
28 |
Ni |
Nickel |
29 |
Cu |
Copper |
30 |
Zn |
Zinc |
31 |
Ga |
Gallium |
32 |
Ge |
Germanium |
33 |
As |
Arsenic |
34 |
Se |
Selenium |
35 |
Br |
Bromine |
36 |
Kr |
Krypton |
37 |
Rb |
Rubidium |
38 |
Sr |
Strontium |
39 |
Y |
Yttrium |
40 |
Zr |
Zirconium |
41 |
Nb |
Niobium |
42 |
Mo |
Molybdenum |
43 |
Tc |
Technetium |
44 |
Ru |
Ruthenium |
45 |
Rh |
Rhodium |
46 |
Pd |
Palladium |
47 |
Ag |
Silver |
48 |
Cd |
Cadmium |
49 |
In |
Indium |
50 |
Sn |
Tin |
51 |
Sb |
Antimony |
52 |
Te |
Tellurium |
53 |
I |
Iodine |
54 |
Xe |
Xenon |
55 |
Cs |
Caesium |
56 |
Ba |
Barium |
57 |
La |
Lanthanum |
58 |
Ce |
Cerium |
59 |
Pr |
Praseodymium |
60 |
Nd |
Neodymium |
61 |
Pm |
Promethium |
62 |
Sm |
Samarium |
63 |
Eu |
Europium |
64 |
Gd |
Gadolinium |
65 |
Tb |
Terbium |
66 |
Dy |
Dysprosium |
67 |
Ho |
Holmium |
68 |
Er |
Erbium |
69 |
Tm |
Thulium |
70 |
Yb |
Ytterbium |
71 |
Lu |
Lutetium |
72 |
Hf |
Hafnium |
73 |
Ta |
Tantalum |
74 |
W |
Tungsten |
75 |
Re |
Rhenium |
76 |
Os |
Osmium |
77 |
Ir |
Iridium |
78 |
Pt |
Platinum |
79 |
Au |
Gold |
80 |
Hg |
Mercury |
81 |
Tl |
Thallium |
82 |
Pb |
Lead |
83 |
Bi |
Bismuth |
84 |
Po |
Polonium |
85 |
At |
Astatine |
86 |
Rn |
Radon |
87 |
Fr |
Francium |
88 |
Ra |
Radium |
89 |
Ac |
Actinium |
90 |
Th |
Thorium |
91 |
Pa |
Protactinium |
92 |
U |
Uranium |
93 |
Np |
Neptunium |
94 |
Pu |
Plutonium |
95 |
Am |
Americium |
96 |
Cm |
Curium |
97 |
Bk |
Berkelium |
98 |
Cf |
Californium |
99 |
Es |
Einsteinium |
100 |
Fm |
Fermium |
101 |
Md |
Mendelevium |
102 |
No |
Nobelium |
103 |
Lr |
Lawrencium |
104 |
Rf |
Rutherfordium |
105 |
Db |
Dubnium |
106 |
Sg |
Seaborgium |
107 |
Bh |
Bohrium |
108 |
Hs |
Hassium |
109 |
Mt |
Meitnerium |
110 |
Uun |
Ununnilium |
111 |
Uuu |
Unununium |
112 |
Uub |
Ununbium |
114 |
Uuq |
Ununquadium |
116 |
Uuh |
Ununhexium |
118 |
Uuo |
Ununoctium |