Lesson Notes By Weeks and Term - Senior Secondary School 1
CHEMICAL COMBINATIONS
CHEMICAL COMBINATIONS
SUBJECT: CHEMISTRY
CLASS: SS 1
DATE:
TERM: 2nd TERM
REFERENCE BOOKS
TOPIC: CHEMICAL COMBINATIONS CONTENT 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. ELECTRON DOT REPRESENTATION OF FORMATION OF IONIC COMPOUNDS Formation of sodium chloride Formation of calcium oxide PROPERTIES OF SOME IONIC COMPOUNDS EVALUATION 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 ELECTRON DOT REPRESENTATION OF FORMATION OF COVALENT COMPOUNDS Formation of hydrogen molecule Formation of carbon (iv) oxide PROPERTIES OF COVALENT COMPOUNDS EVALUATION 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. ELECTRON DOT REPRESENTATION TO SHOW FORMATION OF DATIVE BOND Formation of hydroxonium ion (H3O+) Formation of Ammonium ion (NH4+) 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 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 CO2 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 READING ASSIGNMENT New School Chemistry for Senior Secondary School by O.Y Ababio, Pg 55-66 WEEKEND ASSIGNMENT THEORY
WEEK SIX AND SEVEN DATE-----------------
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