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Mass Numbers

Atom

"The Atom"

Mass Numbers of Atoms - Definition

Definition of Mass Numbers: All atoms have a mass number which is derived from calculating the sum of the total number of neutrons and protons in an atomic nucleus of a particular atom.

Mass Numbers = (Number of Protons) + (Number of Neutrons)

Mass Numbers - Atomic Weight
It is necessary to establish the atomic weight to enable you to establish the Mass Number. The atomic weight or mass is, basically, a measurement of the total number of particles in an atom's nucleus. Using the Mass Number you will be able to calculate the number of Neutrons in an atom.

Mass Numbers - How to find Mass Numbers
The mass number is established by rounding the atomic weight to the nearest whole number. The Periodic Table with Atomic Mass will give you the atomic weight, or atomic mass, of the elements. The chemical properties of an element are determined by its Atomic Number not its Mass Number which is why atomic numbers are shown on the Periodic table whilst Mass Numbers are not. Mass numbers equal the total number of heavy, or massive, particles in the nucleus. Subtracting the Atomic number from the Mass Number equals the number of neutrons in the nucleus.

Mass Numbers = Atomic Weight of Element, rounded to nearest whole number

Number of Neutrons = Mass Number - Atomic Number

Mass Numbers - The Mass Numbers of all of the elements
So, if we know the number of protons and neutrons in an atom we can determine the mass number. The unique chart below has been created by www.elementalmatter.info and details all of the elements in the Periodic table, the numbers of protons, the numbers of neutrons and the mass numbers of atoms which relate to  the elements.

Mass numbers - Examples of Mass Numbers
The following examples provide details of how to calculate the mass number.

  • Example 1 - mass number of Gold: The element Gold (Symbol Au) has the Atomic Number of 79. The number of protons in atom of gold is therefore 79. Gold has the Atomic Mass weight of 196.97. Round to the nearest whole number. The mass number of gold is therefore 197.

  • Example 2 - mass number of Silver: The element Silver (Symbol Ag) has the Atomic Number of 47. The number of protons in atom of silver is therefore 47. Silver has the Atomic Mass weight of 107.87. Round to the nearest whole number. The mass number of silver is therefore 108.

  • Example 3 - mass number of Neon: The element Neon (Symbol Ne) has the Atomic Number of 10. The number of protons in atom of neon is therefore 10. Neon has the Atomic Mass weight of 20.18. Round to the nearest whole number. The mass number of neon is therefore 20.

Mass Numbers = Atomic Weight of Element, rounded to nearest whole number

Mass numbers - List of Mass Numbers
The details all of the elements in the Periodic table, the numbers of protons, the numbers of neutrons and the mass numbers of atoms which relate to  the elements in the Periodic Table.

List of Mass Numbers
Hydrogen: H  : 1
Helium : He  : 4
Lithium : Li  : 7
Beryllium : Be  : 9
Boron : B  : 11
Carbon : C  : 12
Nitrogen : N  : 14
Oxygen : O  : 16
Fluorine : F  : 19
Neon : Ne  : 20
Sodium : Na  : 23
Magnesium : Mg  : 24
Aluminium : Al  : 27
Silicon : Si  : 28
Phosphorus : P  : 31
Sulfur : S  : 32
Chlorine : Cl  : 35
Argon : Ar  : 40
Potassium : K  : 30
Calcium : Ca  : 40
Scandium : Sc  : 45
Titanium : Ti  : 48
Vanadium : V  : 51
Chromium : Cr  : 52
Manganese : Mn  : 55
Iron : Fe  : 56
Cobalt : Co  : 58
Nickel : Ni  : 58
Copper : Cu  : 64
Zinc : Zn  : 65
Gallium : Ga  : 70
Germanium : Ge  : 73
Arsenic : As  : 75
Selenium : Se  : 79
Bromine : Br  : 80
Krypton : Kr 84
Rubidium : Rb  : 85
Strontium : Sr  : 88
Yttrium : Y  : 89
Zirconium :  Zr  : 91
Niobium : Nb 93
Molybdenum :  Mo  : 96
Technetium: Tc  : 98
Ruthenium : Ru  : 101
Rhodium : Rh  : 103
Palladium : Pd  : 106
Silver : Ag  : 108
Cadmium : Cd  : 112
Indium : In  : 115
Tin : Sn  : 119
Antimony : Sb  : 122
Tellurium : Te  : 128
Iodine : I  : 127
Xenon : Xe  : 131
Cesium : Cs  : 133
Barium : Ba  : 137
Lanthanum : La  : 139
Cerium : Ce  : 140
Praseodymium : Pr  : 141
Neodymium : Nd  : 144
Promethium : Pm  : 145
Samarium : Sm  : 150
Europium : Eu  : 152
Gadolinium : Gd  : 157
Terbium : Tb: 159
Dysprosium : Dy 163
Holmium : Ho:  165
Erbium : Er:  167
Thulium : Tm:  169
Ytterbium : Yb:  173
Lutetium : Lu:  175
Hafnium : Hf:  178
Tantalum : Ta:  181
Tungsten : W:  184
Rhenium : Re:  186
Osmium : Os:  190
Iridium : Ir: 192
Platinum : Pt:  195
Gold : Au:  197
Mercury : Hg:  201
Thallium : Tl:  204
Lead : Pb:  207
Bismuth : Bi: 209
Polonium : Po:  209
Astatine : At:  210
Radon : Rn:  222
Francium : Fr:  223
Radium : Ra:  226
Actinium : Ac:  227
Thorium : Th:  232
Protactinium : Pa:  231
Uranium : U:  238
Neptunium : Np:  237
Plutonium : Pu:  244
Americium Am:  243
Curium : Cm:  247
Berkelium : Bk:  247
Californium : Cf:  251
Einsteinium : Es:  252
Fermium : Fm:  257
Mendelevium : Md:  258
Nobelium : No:  259
Lawrencium : Lr:  262
Rutherfordium : Rf:  261
Dubnium : Db:  268
Seaborgium : Sg:  263
Bohrium : Bh:  264
Hassium : Hs:  269
Meitnerium : Mt:  268
Darmstadtium : Ds:  272
Roentgenium : Rg:  273
Ununbium : Uub:  277
Ununtrium : Uut:  286
Ununquadium : Uuq:  289
Ununpentium : Uup:  288
Ununhexium : Uuh:  292
Ununseptium : Uus:  292
Ununoctium : Uuo:  293
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