# Atomic Mass and Moleculer Mass

## ATOMIC MASS

The mass of one atom is called as atomic mass
Atomic mass is given in amu (Atomic Mass Unit).

### (AMU): -

It is the mass of C -12 carbon atom. It is also known as unified mass and denoted by u
1 amu =1.660056 × 10-24 g
Atomic Mass of the elements are expressed in terms of amu.
Atomic Mass of element in amu= Mass of atom in grams / 1.660056 × 10-24

## AVERAGE ATOMIC MASS

Many natural occurring elements exists as more than one isotope. They occur in various percentage. So, we calculate average atomic mass of the elements using the percentage of the isotopes

Example
Chlorine has two isotopes of atomic mass units 34.97 and 36.97. The relative abundance of the isotopes is 75.5 % and 24.5% respectively. Find the average atomic mass of chlorine.
Solution
Average atomic mass = 34.97 x 0.755 +36.97 x 0.245 = 35.46 u

## MOLECULAR MASS

Mass of molecule is the sum of masses of elements present in molecule
Example
Molecular Mass of CO2 = Atomic mass of C + 2 × atomic mass of Oxygen
=12 +2 × 16= 44 amu or 44 u

Molecular Mass of H2O = Atomic mass of O + 2 × atomic mass of Hydrogen
=16 +2 × 1= 18 amu

## Formula Mass-

It is the sum of atomic masses of the elements present in one formula unit of a compound. It is used for the ionic compounds  like NaCL
Formula Mass for NaCl = Atomic mass for Sodium + Atomic Mass for Cl atom
=23 +35.5 = 58.5 u

## List of Atomic Mass of all the Elements

 Elements Symbol Atomic Mass Actinium Ac 227 Aluminum Al 26.9815 Americium Am 243 Antimony Sb 121.76 Argon Ar 39.948 Arsenic As 74.9216 Astatine At 210 Barium Ba 137.327 Berkelium Bk 247 Beryllium Be 9.0122 Bismuth Bi 208.9804 Bohrium Bh 264 Boron B 10.811 Bromine Br 79.904 Cadmium Cd 112.411 Calcium Ca 40.078 Californium Cf 251 Carbon C 12.0107 Cerium Ce 140.116 Cesium Cs 132.9055 Chlorine Cl 35.453 Chromium Cr 51.9961 Cobalt Co 58.9332 Copper Cu 63.546 Curium Cm 247 Dubnium Db 262 Dysprosium Dy 162.5 Einsteinium Es 252 Erbium Er 167.259 Europium Eu 151.964 Fermium Fm 257 Fluorine F 18.9984 Francium Fr 223 Gadolinium Gd 157.25 Gallium Ga 69.723 Germanium Ge 72.64 Gold Au 196.9665 Hafnium Hf 178.49 Hassium Hs 277 Helium He 4.0026 Holmium Ho 164.9303 Hydrogen H 1.0079 Indium In 114.818 Iodine I 126.9045 Iridium Ir 192.217 Iron Fe 55.845 Krypton Kr 83.8 Lanthanum La 138.9055 Lawrencium Lr 262 Lead Pb 207.2 Lithium Li 6.941 Lutetium Lu 174.967 Magnesium Mg 24.305 Manganese Mn 54.938 Meitnerium Mt 268 Mendelevium Md 258 Mercury Hg 200.59 Molybdenum Mo 95.94 Neodymium Nd 144.24 Neon Ne 20.1797 Neptunium Np 237 Nickel Ni 58.6934 Niobium Nb 92.9064 Nitrogen N 14.0067 Nobelium No 259 Osmium Os 190.23 Oxygen O 15.9994 Palladium Pd 106.42 Phosphorus P 30.9738 Platinum Pt 195.078 Plutonium Pu 244 Polonium Po 209 Potassium K 39.0983 Praseodymium Pr 140.9077 Promethium Pm 145 Protactinium Pa 231.0359 Radium Ra 226 Radon Rn 222 Rhenium Re 186.207 Rhodium Rh 102.9055 Roentgenium Rg 272 Rubidium Rb 85.4678 Ruthenium Ru 101.07 Rutherfordium Rf 261 Samarium Sm 150.36 Scandium Sc 44.9559 Seaborgium Sg 266 Selenium Se 78.96 Silicon Si 28.0855 Silver Ag 107.8682 Sodium Na 22.9897 Strontium Sr 87.62 Sulfur S 32.065 Tantalum Ta 180.9479 Technetium Tc 98 Tellurium Te 127.6 Terbium Tb 158.9253 Thallium Tl 204.3833 Thorium Th 232.0381 Thulium Tm 168.9342 Tin Sn 118.71 Titanium Ti 47.867 Tungsten W 183.84 Uranium U 238.0289 Vanadium V 50.9415 Xenon Xe 131.293 Ytterbium Yb 173.04 Yttrium Y 88.9059 Zinc Zn 65.39 Zirconium Zr 91.224