Cations are positively charged ions that form when an atom loses one or more electrons. Cations are usually formed from metal atoms that tend to lose electrons to achieve a stable electron configuration similar to a noble gas. When an atom loses one or more electrons, it forms a cation. The resulting cation has the electronic configuration of a noble gas. Neutral atoms have equal number of protons and electrons. When an atom loses one or more electrons, the number of protons becomes greater than electrons, as a result atom acquires positive charge.
Describe the formation of Na⁺ and Mg⁺² cations.
(a) Formation of Na⁺ ion
Na 1s² 2s² 2p⁶ 3s¹ (-e) → Na⁺ 1s² 2s² 2p⁶
(b) Formation of Mg ion
Mg 1s² 2s² 2p⁶ 3s² (-2e) → Mg⁺² 1s² 2s² 2p⁶
Describe the formation of cations for the following metal atoms:
(a) Li (atomic no 3)
(b) Al (atomic no.12)
Anions are negatively charged ions that form when an atom gains one or more electrons. This process usually occurs when an atom has a relatively high electron affinity, meaning that it can easily attract and capture more electrons to achieve a stable electron configuration similar to a noble gas. When an atom gains one or more electrons, the number of electrons becomes greater than protons, so it acquires negative charge.
Describe the formation of anions for the following non-metal atoms:
(a) Oxygen (atomic no.8)
(b) Fluorine (atomic no. 9)
(a) Formation of anion by oxygen atom:
Oxygen belongs to Group VIA on the periodic table. So it has six electrons in its valence shell. It needs two electrons to achieve noble gas configuration.
O 1s² 2s² 2p⁴ +2e⁻ → O⁻² 1s² { 2s² 2p⁶ } octet
(b) Formation of anion by fluorine atom:
Fluorine belongs to Group VIIA on the periodic table. So it has seven electrons in the valence shell. A fluorine atom therefore, requires only one electron to complete octet.
F 1s² 2s² 2p⁵ + e⁻ → F⁻ 1s² } 2s² 2p⁶} octet
Describe the formation of anions by the following non-metals:
(a) Sulphur (atomic No. 16)
(b) Chlorine(atomic No. 17)