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Atomic Number

February 6, 2013

Atomic Number (chem)

An atom consists of sub atomic particles like negative particle electrons, positive particle protons and neutral particle neutrons.

There are two properties distinguishing one atom from another and that is according to the number of sub atomic particles present in an element. The two important identities of an atom is atomic number and atomic mass or mass number.

Atomic Mass Number is equal to the total weight of an atom. The total weight of atoms is equal to the number of protons, neutrons and electrons present in an element. But most of the elements weights is only according to their mass of the protons and neutrons in that nucleus. The electrons present in an element is very less, thus it is negligible. The sum of the mass of the protons and neutrons present in the nucleus is called as atomic mass.

Atomic mass = Mass of the Protons + Mass of the neutrons + Mass of the Electrons

Mass of the electrons = 0.0005449 = negligible

So,

Atomic mass = Mass of the Protons + Mass of the neutrons

Atomic number is defined as the total number of positive charges like protons present in the nucleus of an atom.

Nuclear charge is defined as the positive charge carried by the nucleus and is equal to the total number of positive charges like protons present on the nucleus of the atom of the element. Atomic mass is denoted by the symbol  Z.

Atomic number = Number of the protons in an atom

The number of positively charged particles or the number of protons present in the nucleus is equal to the number of negatively charged particles or the number of electrons which revolving around the nucleus.

Consequently, the number of protons in the nucleus is equal to the number of electron revolving around the nucleus.

Atomic number = = Number of the protons in the nucleus = Number of the electrons around the nucleus

Z = p = e

The serial number of the elements position in the periodic table is also called as atomic number of an element.  For example hydrogen is the first element in the periodic table and its atomic-number is 1.

While comparing atomic mass and atomic-number, atomic mass is the number of protons and neutrons present in the nucleus and atomic-number is the number of positively charged protons present in the nucleus or the number of negatively charged electrons present around the nucleus.

In periodic table, atomic-number is representing in subscripts of an elemental symbol and mass number is representing in the superscript of an elemental symbol.

For Example

Atomic-Number of Na = 11 (Number of Proton)

Mass Number of Na = 23 (Number of proton + Number of electron)

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