Chemical Bonding

Electrovalent compounds or ionic compounds are usually soluble in water, but insoluble in organic solvents like ether, acetone, benzene, carbon disulphide and carbon tetrachloride. 'Like dissolves like': Ionic compounds dissolve in polar or ionic solvents. Water has a high dielectric constant. Water easily breaks the strong electrostatic force of attraction. The water molecule is polar in nature. The positively charged hydrogen atoms surround the anion. The negatively charged OH- (hydroxyl) surround the cation. Hence, the cation is separated from the anion, breaking the crystal lattice. The organic solvents contain non-polar molecules. Therefore, they are unable to break the electrostatic forces of attraction.

Ionic compounds conduct electricity when dissolved in water. They also conduct electricity when melted. They do not conduct electricity in the solid state. In the solid state, the ions are held together in fixed positions by the electrostatic forces of attraction. Therefore, the ions are not free.

Ionic compounds have a high density. They are generally heavier than water. The oppositely charged ions in an ionic compound are held very closely by strong electrostatic forces of attraction, resulting in the number of ions per unit volume increases. Consequently, increasing in mass per unit volume of the compound.

The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction. London forces are the attractive forces that cause nonpolar substances to condense to liquids and to freeze into solids when the temperature is lowered sufficiently.

Size of the cation involved in bonding is smaller compared to the neutral atom. A cation loses electrons, so there is a reduction in the number of shells. Hence, the size of the ion becomes smaller.

All are the properties of ionic solids.

Size of the cation involved in bonding is smaller compared to the neutral atom. A cation loses electrons, so there is a reduction in the number of shells. Hence, the size of the ion becomes smaller.

As its name implies, it is the strongest force of the four. However, it also has the shortest range, meaning that particles must be extremely close before its effects are felt. Its main job is to hold together the subatomic particles of the nucleus (protons, which carry a positive charge, and neutrons, which carry no charge. These particles are collectively called nucleons.

The covalent bonding occurs when two (or more) elements share electrons. Covalent bonding occurs because the atoms in the compound have a similar tendency for electrons (generally to gain electrons). The ionic bonding is a one in which a complete transfer of electrons takes place between the atoms.

Due to non-directional nature of the polar bonds present in these compounds they do not exhibit isomerism.

A magnesium atom needs to lose two electrons, whereas the nitrogen atom needs to gain three electrons to attain the octet.The chemical formula for magnesium nitride is Mg₃N_2. Two magnesium atoms donate two electrons to each nitrogen atom while one magnesium atom donates one electron to each of the nitrogen atom. Hence, an ionic bond is formed. Magnesium and nitrogen, thus, attain stability by gaining the octet state.

Since covalent compounds do not give ions in solution, these are poor conductors of electricity in the fused or dissolved state.

A molecule of oxygen contains two oxygen atoms joined by a double covalent bond.Thus, the two atoms of oxygen share two electrons each and do not require any more electrons because they have already attained stable octet configurations. If an atom of oxygen having six electrons comes closer to the oxygen molecule, the new atom may share a lone pair of electrons from either of these two oxygen atoms, which donates to the third oxygen atom without sharing any of the electrons of the third oxygen atom. As a result, a coordinate bond is formed between one of the oxygen atoms of the oxygen molecule, and the third atom of oxygen.

The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction. Van der Waals-London forces grow with the length of the nonpolar part of the substance.

The dipole moment of carbon dioxide is zero. This is because CO2 is a linear molecule in which the two C=O (m=2.3D) bonds are oriented in opposite directions at an angle of 180°. Due to the linear geometry the dipole moment of one C = O bond cancels that of another. Therefore, the resultant dipole moment of the molecule is zero and it is a non-polar molecule.

All of the above factors favours the formayion of  covalent bonds.

Ionic compounds have high melting and boiling points. For example, sodium chloride has a high melting point of 1472 ^oF and boiling point of 2575.4 ^oF. Lithium chloride has a melting point of 1122.8 ^oF and boiling point of 2462 ^oF. Potassium chloride has a melting point of 1526 ^oF and boiling point of 2732 ^oF. As these compounds contain ions held together by strong electrostatic forces, very high amount of energy is required to overcome this force and break the crystal lattice. This explains the high melting point and boiling point of ionic compounds.

Since covalent compounds are made up of neutral molecules, if they dissolve in water they do not dissociate into ions. Example: Alcohol is soluble in water but does not dissociate to give ions.

It is a special type of a covalent bond wherein the shared pair of electrons is supplied by only one of the bonding atoms. A lone pair of electrons is present in one of the atoms.e.g.Hydronium ion [H3O⁺ ] It is formed by the combination of water molecule and hydrogen ion. The oxygen atom in a water molecule has two lone pairs of electrons. It donates one pair to the hydrogen ion. Oxygen is thus the donor and hydrogen ion, the acceptor. The hydrogen ion carries over its charge to the hydronium ion.

Ionic compounds are hard crystalline solids. The crystal of sodium chloride has a definite shape. There is a strong electrostatic force of attraction, which holds the ions together. The ions cannot be easily separated. The crystals are hard and brittle.

The hydrogen bond is really a special case of dipole forces. A hydrogen bond is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge.

These measure the tendency of an atom to accept electrons. The atoms with high electronegativity and electron affinity readily form anion and hence ionic compounds.

These measure the tendency of an atom to accept electrons. Therefore, atoms with high electronegativity and electron affinity readily form anion and hence ionic compounds.

An atom with low ionization energy, readily loses electron. So it forms the cation readily and produce ionic compounds. Ex: Potassium gives the cation more readily than sodium because the ionization potential of potassium is less than the sodium atom.

In a triple bond, six electrons attract the nuclei with greater force, out of the three types of bond length. This decreases the distance of separation between the two nuclei the most. Hence the bond length is shortest in triple bond.Since, a shorter bond means greater bond strength hence, the energy required to separate the bonded atoms is maximum.