B) Ionic BondsOppositely charged ions have a strong mutual electrostatic attraction when brought together, but, if brought too close, the electron clouds repel each other. Thus, a pair of mutually attracted ions will maintain a certain distance from each other. This distance is called the bond length, and the electrostatic attraction of the ions constitutes an ionic (or electrovalent) bond.
Ionic bonds are very common and are exemplified by table salt, in which a sodium ion attracts a chloride ion to form Na+Cl- or, as usually written, NaCl. Calcium ions (Ca2+) and chloride ions (Cl- ) combine in a one-to-two ratio to form calcium chloride, CaCl2. The total charge on each combination of ions, NaCl and CaCl2, is neutral, or zero.
C) Covalent BondsWhen two atoms share a pair of electrons, they form a covalent bond. When atoms bond covalently, they form molecules. A molecule can be made up of two or more atoms, all joined with covalent bonds. Each atom can share its electrons with one or more other atoms. Some molecules contain chains of thousands of covalently bonded atoms.
2) Types of Covalent Bonds A) Non-polar covalent bondA covalent bond formed between two like atoms is known as Non-polar bond. Since difference of electro negativity is zero therefore, both atoms attract electron pair equally and no charge appears on any atom and the whole molecule becomes neutral.
b)Polar covalent bondsA covalent bond formed between two different atoms is known as Polar covalent bond. For example when a Covalent bond is formed between H and Cl , it is polar in nature because Cl is more electronegative than H atom . Therefore, electron cloud is shifted towards Cl atom. Due to this reason a partial -ve charge appeared on Cl atom and an equal +ve charge on H atom.
C) Coordinated covalent bondsA coordinate covalent bond is when two atoms have a covalent bond where the two electrons that are shared by the atoms in the bond come from only one of the atoms. This bond does not have any different properties than a polar covalent bond it is just named differently to show that the electrons came from an atom with a lone pair. This occurs when a Lewis base donates electrons to a Lewis acid.
3)Types of intermolecular forcesIt is important to be able to recognise whether the molecules in a substance are polar or non-polar because this will determine what type of intermolecular forces there are. This is important in explaining the properties of the substance.
*Dispersion forces (London forces) Dispersion forces exist between all small covalent molecules Electrons within the molecule momentarily shift away from one side of the molecule, setting up a momentary temporary dipole. The attraction between the and of the temporary dipoles is called the dispersion force. This is an attractive force! Dispersion forces are stronger for larger molecules and for straight chain molecules.
*Dipole-Dipole forces Dipole-dipole forces exist only between polar molecules A dipole-dipole force is the attraction of the part of one molecule and the part of a neighbouring molecule. Dipole-dipole forces are stronger when molecules are more polar. Polar molecules contain polar bonds and are asymmetrical in shape.