Atomic Structure

Construction Of A Matter :

Any matter in this Universe can exist in the form of solid, liquid or gas as in the case of stone, water and air respectively. The smallest particle of matter that retains the properties of the original matter is known as a molecule. A molecule consists of two or more atoms which are known as the basic building blocks of that matter.

An atom is the smallest particle of a molecule which contains within itself three fundamental particles which are known as elections, protons and neutrons.

Electron is a negatively charged particle with a unit of negative charge. The weight of an electron is 1840 times less than the weight of a proton.

Proton is a positively charged particle with a unit of positive charge. A proton is near about 1840 times heavier than an electron.

Neutron is an electrically neutral particle without any unit of positive and negative charge. A neutron is approximately as heavy as a proton.

All matters in this universe exist in the form of elements and compounds.

If all atoms in the molecule of a substance are identical then that substance is known as an element. Copper, silver, gold, etc. are examples of elements. There are approximately 114 known elements available in the universe.

If the molecule of a substance consists of two or more atoms which are not identical then that substance is known as compound. There are unlimited number of compounds available in the universe.

Water (H2O) is an example of a compound because it consists of atoms of hydrogen and oxygen which are not identical.

Similarly, Sodium Chloride (NaCl) is also a compound because it consists of dissimilar atoms of sodium & chlorine.

Structure Of An Atom :

According to the Danish Scientist Neils Bohr, the structure of an atom is similar to our planetary system in which different planets like Earth, Mars, Venus, etc. revolve round the Sun in their different orbits.

In the case of an atom, there is a central part which is known as nucleus that contains all protons with their positive charge and all neutrons without any electrical charge. The electrons with their negative charge revolve round the nucleus in their different orbits away from the nucleus.

For a neutral atom, the total number of revolving electrons in the different orbits are always equal to the total number of protons in the nucleus.

The atomic number of any element is given by the total number of electrons revolving round the nucleus or by the total number of protons available in the nucleus.

The orbits of the revolving electrons are also known as shells or energy levels which are from the nucleus outwards known as K, L, M, N, O & P shells.

Each of these shells can accommodate a maximum number of electrons for stability which is given by the formula 2*N^2 where N = 1, 2, 3, 4, 5 & 6 respectively for K, L, M, N, O & P Shells.

After any shell is completed with the maximum number of electrons it can contain, the remaining electrons arrange themselves in higher orbits.

Therefore,

The maximum number of electrons for K shell = 2 * (1 * 1) = 2 * 1 = 2.

The maximum number of electrons for L shell = 2 * (2 * 2) = 2 * 4 = 8.

The maximum number of electrons for M shell = 2 * (3 * 3) = 2 * 9 = 18.

The maximum number of electrons for N shell = 2 * (4 * 4) = 2 * 16 = 32.

The maximum number of electrons for O shell = 2 * (3 * 3) = 2 * 25 = 18.

The maximum number of electrons for P shell = 2 * (2 * 2) = 2 * 4 = 8.

The rule of 2*N^2 is not applicable for the last orbit and the second last orbit of an atom. The maximum number of electrons in the last orbit of an atom does not exceed 8 and in the second last orbit it does not exceed 18.

The outermost orbit of an atom is known as Valence Shell and the electrons in this orbit are known as Valence Electrons. These valence electrons are far away from the nucleus and hence, they have highest energy level due to loose attachment with the nucleus.

The atomic number and the arrangement of three fundamental particles in an atom of any material determine physical & chemical properties of that material and accordingly, materials are classified as conductors, insulators and semiconductors according to their capacity to conduct electricity.

Conductor :

Conductor is a material which allows electric current to flow through it easily. Gold, Silver, Copper, Aluminium, etc. are examples of conductor.

When the number of electrons in the last orbit of an atom of a material are less than 4 then that material behaves like a conductor.

Insulator :

Insulator is a material which does not allow electric current to flow through it easily. Wood, Rubber, Plastic, Glass, etc. are examples of insulator.

When the number of electrons in the last orbit of an atom of a material are more than 4 then that material behaves like an insulator.

Semiconductor :

Semiconductor is a material which partially allows electric current to flow though it and partially offers opposition to the flow of electric current. Therefore, it is neither good conductor nor good insulator and hence, it is known as semiconductor. Silicon, Germanium, Tin, Selenium and Tellurium are examples of semiconductor.

When the number of electrons in the last orbit of an atom of a material are exactly 4 then that material behaves like a semiconductor.

Mock Test On Atomic Structure