Reference:

Periodic Table of the Elements

Infographic: the chemical elements organized according to the number of protons in each nucleus
The classic Periodic Table organizes the chemical elements according to the number of protons that each has in its atomic nucleus.
Credit: Karl Tate, Livescience.com contributor

The Periodic Table of the Elements arranges all of the known elements in an informative array. Elements are arranged in order of increasing atomic number. Order generally coincides with increasing atomic mass.

The different rows of elements are called periods. The period number of an element signifies the highest energy level an electron in that element occupies (in the unexcited state), according to the Los Alamos National Laboratory. The number of electrons in a period increases as one moves down the periodic table; therefore, as the energy level of the atom increases, the number of energy sub-levels per energy level increases.

Elements that lie in the same column on the periodic table (called a "group") have identical valance electron configurations and consequently behave in a similar fashion chemically. For instance, all the group 18 elements are inert gases. [Related: How Are the Elements Grouped?]

The periodic table contains an enormous amount of important information:  

Atomic Number: The number of protons in an atom defines what element it is. For example, carbon atoms have six protons, hydrogen atoms have one, and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element. The number of protons in an atom also determines the chemical behavior of the element.

Element Symbol: The element symbol is one, two or three letters chosen to represent an element ("H" for hydrogen, "Kr" for krypton, "Uup" for Ununpentium, etc.). These symbols are used internationally. 

Atomic Weight: The standard atomic weight is the average mass of an element in atomic mass units ("amu"). Though individual atoms always have an integer number of atomic mass units, the atomic mass on the periodic table is stated as a decimal number because it is an average of the various isotopes of an element. The average number of neutrons for an element can be found by subtracting the number of protons (atomic number) from the atomic mass.

Atomic weight for elements 93-118: For naturally occurring elements, the atomic weight is calculated from averaging the weights of the natural abundances of the isotopes of that element. However, for man-made trans-uranium elements there is no "natural" abundance. The convention is to list the atomic weight of the longest-lived isotope in the periodic table. These atomic weights should be considered provisional since a new isotope with a longer half-life could be produced in the future.

Within this man-made category are the superheavy elements, or those with atomic numbers above 104. The larger the atom's nucleus — which increases with the number of protons inside — the more unstable that element is, generally. As such, these outsized elements are fleeting, lasting mere milliseconds before decaying into lighter elements, according to the International Union of Pure and Applied Chemistry (IUPAC). For instance, superheavy elements 113, 115, 117 and 118 were just verified by the IPUAC in December 2015, completing the seventh row, or period, on the table. Several different labs produced the superheavy elements.

"The chemistry community is eager to see its most cherished table finally being completed down to the seventh row. IUPAC has now initiated the process of formalizing names and symbols for these elements," Jan Reedijk, president of the Inorganic Chemistry Division of IUPAC, said in an IUPAC statement.

Element articles

Element No. Sym Element No. Sym Element No. Sym
Actinium 89 Ac Hafnium 72 Hf Protactinium 91 Pa
Aluminum 13 Al Hassium 108 Hs Radium 88 Ra
Americium 95 Am Helium 2 He Radon 86 Rn
Antimony 51 Sb Holmium 67 Ho Rhenium 75 Re
Argon 18 Ar Hydrogen 1 H Rhodium 45 Rh
Arsenic 33 As Indium 49 In Roentgenium 111 Rg
Astatine 85 At Iodine 53 I Rubidium 37 Rb
Barium 56 Ba Iridium 77 Ir Ruthenium 44 Ru
Berkelium 97 Bk Iron 26 Fe Rutherfordium 104 Rf
Beryllium 4 Be Krypton 36 Kr Samarium 62 Sm
Bismuth 83 Bi Lanthanum 57 La Scandium 21 Sc
Bohrium 107 Bh Lawrencium 103 Lr Seaborgium 106 Sg
Boron 5 B Lead 82 Pb Selenium 34 Se
Bromine 35 Br Lithium 3 Li Silicon 14 Si
Cadmium 48 Cd Livermorium 116 Lv Silver 47 Ag
Calcium 20 Ca Lutetium 71 Lu Sodium 11 Na
Californium 98 Cf Magnesium 12 Mg Strontium 38 Sr
Carbon 6 C Manganese 25 Mn Sulfur 16 S
Cerium 58 Ce Meitnerium 109 Mt Tantalum 73 Ta
Cesium 55 Cs Mendelevium 101 Md Technetium 43 Tc
Chlorine 17 Cl Mercury 80 Hg Tellurium 52 Te
Chromium 24 Cr Molybdenum 42 Mo Terbium 65 Tb
Cobalt 27 Co Neodymium 60 Nd Thallium 81 Tl
Copernicium 112 Cn Neon 10 Ne Thorium 90 Th
Copper 29 Cu Neptunium 93 Np Thulium 69 Tm
Curium 96 Cm Nickel 28 Ni Tin 50 Sn
Darmstadtium 110 Ds Niobium 41 Nb Titanium 22 Ti
Dubnium 105 Db Nitrogen 7 N Tungsten 74 W
Dysprosium 66 Dy Nobelium 102 No Ununoctium 118 Uuo
Einsteinium 99 Es Osmium 76 Os Ununpentium 115 Uup
Erbium 68 Er Oxygen 8 O Ununseptium 117 Uus
Europium 63 Eu Palladium 46 Pd Ununtrium 113 Uut
Fermium 100 Fm Phosphorus 15 P Uranium 92 U
Flerovium 114 Fl Platinum 78 Pt Vanadium 23 V
Fluorine 9 F Plutonium 94 Pu Xenon 54 Xe
Francium 87 Fr Polonium 84 Po Ytterbium 70 Yb
Gadolinium 64 Gd Potassium 19 K Yttrium 39 Y
Gallium 31 Ga Praseodymium 59 Pr Zinc 30 Zn
Germanium 32 Ge Promethium 61 Pm Zirconium 40 Zr
Gold 79 Au            

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