Chemical Combinations: Electrovalent, Covalent, Dative, Hydrogen and Metallic bond

CONTENT

• Electrovalent (ionic) bond
• Covalent bond
• Dative bond
• Hydrogen bond
• Metallic bond

ELECTROVALENT (IONIC) BOND

Electrovalent bond is characterised by transfer of electrons from metallic atoms to non-metallic atoms during reaction. The metallic atom that donates electron becomes positively charged while the non-metallic atom that accepts electron becomes negatively charged. The strong electrostatic attraction that holds the oppositely charged ions together is called ionic bond.

PROPERTIES OF SOME IONIC COMPOUNDS

1. They are solids at room temperature.
2. They contain oppositely charged ions.
3. They readily dissolve in water and other polar solvents like ethanol.
4. They have high melting and boiling points
5. They are good conductors of electricity when in molten or in aqueous form.

EVALUATION

1. How is an ionic compound formed?
2. State the properties of ionic compound

COVALENT BOND

This involves the sharing of a paired of electron between two reacting atoms. The shared electrons are each contributed by the reacting atoms and are called shared pair. A shared pair of electron in covalent bond is represented by a horizontal line

(—-) between the two atoms

PROPERTIES OF COVALENT COMPOUNDS

1. They consist of molecules with definite shape.
2. They are gases or volatile liquids.
3. They readily dissolve is non-polar organic solvents
4. They have low melting and boiling points
5. They do not conduct electricity because the molecules do not contain charged particles.

EVALUATION

1. What is covalent bond?
2. Outline the properties of covalent compounds

COORDINATE COVALENT (DATIVE) BOND

In coordinate covalent bond, the shared pair of electrons is supplied by one of the combining atoms. Coordinate covalent bond is often formed in molecules that have a lone pair of electrons, i.e. a pair of electron not directly concerned in an existing bond.

Compounds containing coordinate covalent bond are similar in properties to purely covalent compounds. Both do not conduct electricity, but the presence of coordinate covalent bond tends to make a compound less volatile.

HYDROGEN BOND

Hydrogen bond is a dipole-dipole intermolecular force of attraction which exists when hydrogen is covalently bonded to a highly electronegative element of small atomic size. The electronegative element can be N, O, F, Cl, Br or I.

The highly electronegative element has very strong affinity for electrons. Hence, they attract the shared pair of electrons in the covalent bond toward themselves, resulting in the formation of a dipole which leaves a partial positive charge on the hydrogen atom and a partial negative charge on the electronegative atom. An electrostatic attraction between two dipoles is set up when the positive pole of one molecule attracts the negative pole of the other. This attractive force is known as hydrogen bond.

IMPORTANCE OF HYDROGEN BOND

It accounts for the solubilities of some compounds containing O, N and F in certain hydrogen containing solvents such as water

The crystalline shape of solid water (ice) is due to hydrogen bond.

EVALUATION

1. Define hydrogen bond

2. State two importance of hydrogen bond.

METALLIC BOND

Metal atoms are held together in solid crystal lattice by metallic bond. each metallic atom contributes its outer (valence) electron to the electron cloud, thus becoming positively charged. The resulting positively charged metallic ions tend to repel each other but are held together by the moving electron cloud and overlapping residual electron orbits. Thus, a metallic bond is a force of attraction between the positive metal ions and the free mobile electrons.

VAN DER WAALS’ FORCES

The attractive forces which make it possible for non-polar molecules like nitrogen and CO^­₂ molecules to form liquid and solid is called van der Waals’ force. This force though very weak when compared to ionic and covalent bond is important in the liquefaction of gases and in the formation of molecular lattices as in iodine and naphthalene crystals.

GENERAL EVALUATION/REVISION

1. Using electron dot representation, show the formation of MgO and O2 molecule
2. Define hydrogen bond
3. How is metallic bond formed?
4. Describe how you will separate a mixture of NaCl, Iodine and PbCl₂

READING ASSIGNMENT

New School Chemistry for Senior Secondary School by O.Y Ababio, Pg 55-66

WEEKEND ASSIGNMENT

1. Noble gases are stable because they A. are volatile B. have octet configuration C. have no neutron in their nucleusD. forms ions easily
2. The bond type in diatomic nitrogen gas is A. double covalent bondB. triple covalent bondC. single covalent bondD. double electrovalent bond
3. In electrovalency, valence electrons are transferred and the atomic number is A. reduced B. stabilized C. unaffected D. increased
4. An element Y having an atomic number of 19 combines with another element Z with     atomic number 17. The likely compound formed is A. Y₂Z B. Y₃Z₂C. YZ D. Y₂Z₂
5. The type of attractive force which exist between discrete molecules is calledA. metallic bond

B. hydrogen bondC. dative bondD.van der Waals’ forces

THEORY

1. A. Illustrate the formation of the compound AlCl3 using electron dot representation

B. State two properties of the compound

Define hydrogen bond