Page 58 - Chemistry_Form_2

Chemistry
for Secondary Schools

Questions
1. Which substance(s) dissolved easily in water? Explain your answer.
2. Which substances are electrovalent? Write their constituent ions.

FOR ONLINE READING ONLY
Exercise 3.1

1. Explain why cations are slightly smaller than their neutral atoms, whereas
anions are slightly larger than their neutral atoms.
2. Magnesium and oxygen atoms combine to form magnesium oxide.

(a) What is the charge on the magnesium ion in the oxide?
(b) What is the charge on the oxide ion?

(c) Illustrate the electron transfer using dots.
3. Why NaCl is soluble in water but not in oil, and how does chemical bonding
explain this?

Covalent bonding

Covalent bonding occurs when atoms share electrons to achieve a stable electron
configuration, typically similar to that of the nearest noble gas. This type of bond
forms when the atoms involved have similar electronegativities (the ability to
attract electrons). Atoms may gain the noble gas electronic structures without

becoming ions but by sharing the outermost electrons. For example, a hydrogen
atom needs one electron to acquire the helium electronic configuration. It can
combine with another hydrogen atom and share the electrons so that each attain a
stable helium configuration. This results in the formation of a hydrogen molecule
(Figure 3.4). The kind of the bond formed between the two atoms is called a
covalent bond. The covalent bond is a chemical bond formed by the sharing of
one or more electrons between atoms.

Student’s Book Form Two 51

01/08/2025 11:20:55
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 51 01/08/2025 11:20:55
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 51