Grade 9 ion formation notes
- 1. IONS An ion is a charged particle formed when an atom gains or loses electrons from its outer shell. The inert gases do not form ions because their outer shell already contain the maximum number of electrons making these element stable or unreactive. Atoms lose or gain electrons in order to get the stable electronic structure of the nearest noble gas. There are two main types of ions: i. Cations – positively charged ions ii. Anions – negatively charged ions Formation of Cations A cation is formed when a metal atom loses the one, two or three electrons that were on its outer shell. When this happens, the remaining particle becomes positively charged because the nucleus now has more protons than there are electrons orbiting it. The charge on the cation formed is equal to the number of electrons lost. Example: Formation of sodium ion (cation) Sodium atom Sodium ion Na Na+ EC: 2, 8, 1 EC: 2,8 + Sodium atom is neutral since it contains an Sodium cation carries a one positive (+) equal number of protons and electron s charge because it has lost one outer electron. (11P, 11E) It now has one more proton than electrons (11P, 10E) It now has the stable EC of Neon (the nearest noble gas) Formation of Anions An anion is formed when a non-metal atom gains one, two or three electrons on its outermost shell. When this happens, the remaining particle becomes negatively charged because the nucleus now has less protons than there are electrons orbiting it. The charge on the anion formed is equal to the number of electrons gained Example: Formation of oxygen ion (anion) Oxygen atom Oxygen ion O O2− EC: 2,6 EC: 2, 8 2− The oxygen atom is neutral because it contains an The oxygen ion carries a 2− charge because equal number of protons and electrons (8P, 8e) it has gained 2 more outer electrons (8P, 10e). It now has the stable EC of Neon (the nearest noble gas) 11P 12N 11P 12N 23 11 8P 8N 16 8 8P 8N