# Atomic Structure |Structure of Elements

## Atomic Structure

According to modern world theory, the matter is electrical in nature. All the materials are composed of very tiny particles called atoms. The atoms are the building bricks of all things in the visible world. An atom composed of a central nucleus of positive charge around which tiny negatively charged particles, called electrons revolve in different paths or orbits.

### (1) Nucleus.

It is the central part of an atom and *composed of protons and neutrons. A proton is a positively charged, while the neutron has the nearly same mass as the proton, but has zero charges. That’s why the nucleus of an atom is positively charged. The sum of protons and neutrons constitutes all weight of an atom and is called atomic weight. It is due to the particles in the extra nucleus (i.e. electrons) have negligible weight as compared to protons or neutrons.

∴ atomic weight = no. of protons + no. of neutrons

### (2) Extra nucleus.

It is the outside part of an atom and contains only electrons. An electron is a negatively charged particle having nearly zero mass. The charge on an electron is equal but opposite to on a proton. Also, the number of electrons is equal to the number of protons in an atom under normal conditions. That’s why an atom is neutral as a whole. The number of electrons or protons in an atom is known atomic number i.e.

atomic number = no. of protons or electrons in an atom

The electrons in an atom revolve around the nucleus in different orbits or paths. The number and arrangement of electrons in an orbit is found by the following rules :

(i) The number of electrons in orbit is given by 2n, 2 where n is the number of the orbit. For example,

• First orbit contains 2 × 12 = 2 electrons
• Second orbit contains 2 × 22 = 8 electrons
• Third orbit contains 2 × 32 = 18 electrons

(ii) The last orbit cannot have more than 8 electrons.
(iii) The last but one orbit cannot have more than 18 electrons

Structure of Elements

We know that all atoms are made up of protons, neutrons, and electrons. The difference between many types of elements is because of the different number and arrangement of these particles within their atoms. For example, the structure* of a copper atom is more different from that of a structure of carbon atom and hence the two elements have different properties. The atomic structure can be easily made up if we know the atomic weight as well as the atomic number of the element. Thus taking the case of the copper atom,

Atomic weight = 64
Atomic number = 29
∴ No. of protons = No. of electrons = 29
and No. of neutrons = 64 − 29 = 35

Fig. 1.4 shows the structure of the copper atom. It has 29 electrons which are placed in different orbits as follows. The first orbit always has 2 electrons, the second 8 electrons, the third 18 electrons, and the fourth orbit has 1 electron. The atomic structure of all discovered elements can be shown in this way and the reader is advised to try for a few commonly used elements.

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