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^-24g
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