Page 16 - 1202 Question Bank Chemistry Form 4 KSSM

5. The table below shows the melting point and boiling are easily released and delocalised. Positively-
point of chlorine and ethanol. charged metal ions are formed.
3. The delocalised valence electrons move freely
Melting point Boiling point
Substance between the metallic structure and form the sea of
( C) ( C) electrons.
o
o
Chlorine –101.5 –34 4. Therefore, electrostatic force of attraction between
the sea of electrons and metal ions is produced.
Ethanol –114.1 78 Thus, a metallic bond is produced.
6. Although the boiling points of both chlorine and Positively
ethanol are low, the boiling point of ethanol is much Valence + + + + + + + + + + charged
electron
higher than that of chlorine due to the presence of + + + + + + + + + + metal ion
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hydrogen bonds between the two molecules. + + + + + + + + + +
7. More heat energy is required to overcome the van der + + + + + + + + + + + + + + + + + + + +
Waals attraction forces between ethanol molecules
besides breaking the hydrogen bonds between the Delocalised electrons
from “sea of electrons”
ethanol molecules.
8. The solubility of ethanol in water is also due to the 5. Metals can conduct electricity because the
presence of hydrogen bond between ethanol molecule delocalised valence electrons in the sea of electrons
and water molecule. can move freely and carry electrical charges from
the negative terminal to the positive terminal.
5.5 Dative Bond
5.7 Ionic and Covalent Compounds
1. Dative bond is a covalent bond between two atoms
in which the shared pair electrons are originated from 1. Electrical conductivity
one atom only. (a) In solid state, ionic compounds do not conduct
2. Dative bond is also known as coordinate bond. electricity because the ions are attracted to each
3. Hydroxonium ion and ammonium ion are two other by strong electrostatic forces. Hence, these
examples of ions with dative bond. ions cannot move freely.
(a) Hydroxonium ion (b) Ionic compounds can conduct electricity in
molten or aqueous states because ions can
move freely and carry electrical charges.
Hydroxonium ion that
Hydrogen ion without is formed through the (c) Covalent compounds do not conduct electricity
in all states because they are composed of
electron in the shell formation of a dative bond.
H H + neutral molecules. Free moving ions do not
exist.
H O + H + H O H 2. Solubility in Water and Organic Solvent
(a) Most ionic compounds are soluble in water.
(b) Ionic compounds do not dissolve in organic
solvents.
Lone paired electrons in a water molecule are (c) Most covalent compounds are soluble in
contributed to the hydrogen ion to be shared together.
organic solvents.
(b) Ammonium ion (d) Covalent compounds do not dissolve in water.
H + 3. Melting and Boiling Points
H N H + H + H N H (a) Cations and anions in the lattice of ionic
compounds are attracted to each other by strong
H electrostatic forces. More heat energy is required
H to overcome the strong electrostatic forces.
(b) Due to high melting and boiling points, ionic
Ammonium ion is produced through the formation of compounds usually exist as non-volatile solids.
dative bond between hydrogen ion and nitrogen atom (c) Molecules in covalent compounds are attracted
in the ammonia. to each other by weak van der Waals force
of attraction. Less heat energy is needed to
5.6 Metallic Bond overcome the weak van der Waals forces of
1. Metal atoms have 1, 2, or 3 valence electrons. attraction between molecules.
2. Even in solid state, valence electrons of metal atoms (d) Due to low melting and boiling points, covalent
compounds usually exist as volatile liquids.

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