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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
Average Atomic Mass 
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

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