(ATOMIC THEORY 8) BONDING- atomic radius, electronegativity and ionic bonding

Atomic radius

The atomic radius is obtained by getting half the distance between the centres of singly bonded atoms of the same element

There is a decrease in the atomic radius across a period due to

-An increase in nuclear charge (number of protons)

-No change in the number of shells hence the screening effect of completed shells remains the same

There is an increase in atomic radius going down a group due to

-An increase in the number of shells

-The screening effect of electrons in the full inner shells blocks out some of the ‘pull’ the nucleus has on the outer electrons

Electronegativity

The relative power of attraction an atom of an element has for a shared pair of electrons in a covalent bond

Electronegativity values generally increase across a period due to

-An increase in nuclear charge (number of protons increase)

-Leading to a decrease in atomic radius

Electronegativity values generally decrease going down a group due to

-The addition of extra shells making the atomic radius larger

-The increased screening effect of full inner shells on outer shells

Ionic bond

An ionic bond is formed due to the electrostatic force of attraction between oppositely charged ions caused by the complete transfer of electrons from one atom to another

Why are ionic compounds crystalline?

Because they are made up of an orderly arrangement of oppositely charged ions which give rise to a lattice structure

Why are ionic compounds solid?

There are extremely strong forces of attraction between oppositely charged ions which hold the ions tightly together giving a solid structure

Why do ionic compounds have high boiling points/ melting points?

The extremely strong forces of attractions between oppositely charged ions require large amounts of energy to break, hence ionic compounds have high b.p. and m.p.

General properties of ionic compounds

-Ionic compounds are usually solid crystalline compounds due to individual ions attracting other ions (extremely strong forces of attraction)

-Ionic compounds conduct electricity when either molten or dissolved state as ions are free to move

-Ionic compounds dissolve or are soluble in polar solvents, as attraction between the ions in the compound and polar water are strong enough to pull the crystalline lattice apart

-Ionic compounds have high melting and boiling points due to a lot of energy being needed to break the extremely strong forces of attraction between the ions

Ionic materials in everyday life

-Washing soda crystals, Na2CO3, used to soften hard water e.g. Calgon tablets

-Aluminum sulphate, Al2(SO4)2, is used as a flocculating agent in the preparation of water for drinking. It causes small suspended particles to stick together so that they can be filtered off more easily