# Atomic number and atomic mass of elements of periodic table

### The atomic number and mass number

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 electronic structure.

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

### How to calculate the atomic mass unit?

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

### The atomic number of s block elements

 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
 Element Symbol Atomic number Atomic mass Beryllium Be 4 1.008 Magnesium Mg 12 6.940 Calcium Ca 20 22.997 Strontium Sr 38 87.63 Barium Ba 56 137.36 Radium Ra 88 226.05

#### The atomic mass 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 35.457 Bromine Br 35 79.916 Iodine I 53 126.91 Astatine At 85 210

### The atomic number 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 36 83.80 Xenon Xe 54 131.3 Radon Rn 86 222