Atomic Number and Mass Number of Elements

The atomic number is the number of protons present in the nucleus of an atom which represents the chemical properties and position of such element in the periodic table. Thus the properties of an element dictated by its atomic number or number of its electron.

Electron holds the key to the chemical world because the chemical properties of the element understand by its electron configuration. But the number of protons and the number of neutrons together called the mass number of an element.

∴ Mass number = number of electrons + number of protons

The atomic weight of an element is a number that says how much heavy an atom of an element compared to one-twelfth of an atom of the carbon-12 isotope. But the gram atomic weight of an element is the weight in gram.

Atomic mass unit (amu) is exactly the one-twelfth of the mass of a carbon-12 atom. Thus the mass of an atom expressed in amu which numerically equal to its atomic weight on the carbon-12 scale.

1 amu = (12/6.023) × (1/12) × 10-23 gm
= 1.6603 × 10-24 gm

s-block elements with atomic number

Element Symbol Atomic number Atomic
mass
Hydrogen H 1 1.008
Lithium Li 3 6.940
Sodium Na 11 22.997
Potassium K 19 39.100
Rubidium Rb 37 85.480
Cesium Cs 55 132.91
Francium Fr 87 223
Beryllium Be 4 9.013
Magnesium Mg 12 24.32
Calcium Ca 20 40.08
Strontium Sr 38 87.63
Barium Ba 56 137.36
Radium Ra 88 226.05

Name and atomic number of p block elements

Element Symbol Atomic number Atomic
Mass
Boron B 5 10.82
Aluminum Al 13 26.98
Gallium Ga 31 69.72
Indium In 49 114.76
Thallium Tl 81 204.39
Carbon C 6 12.01
Silicon Si 14 28.09
Germanium Ge 32 72.60
Tin Sn 50 118.70
lead Pb 82 207.21
Nitrogen N 7 14.008
Phosphorus P 15 30.975
Arsenic As 33 74.91
Antimony Sb 51 121.76
Bismuth Bi 83 209.00
Oxygen O 8 16.00
Sulfur S 16 32.066
Selenium Se 34 78.96
Tellurium Te 52 127.61
Polonium Po 84 210
Fluorine F 9 19.00
Chlorine Cl 17 35.475
Bromine Br 35 79.916
Iodine I 53 126.91
Astatine At 85 210

The atomic mass of noble gases

Element Symbol Atomic number Atomic
Mass
Helium He 2 4.003
Neon Ne 10 20.183
Argon Ar 18 39.944
Krypton Kr 19 83.80
Xenon Xe 37 131.30
Radon Rn 55 222

Chemical Bond

Parts of an atom

Electronic Structure

Equilibrium

Kinetics

Atomic Number of d-Block Elements

Atomic number and atomic mass of elements of periodic table