Group Numbers in the Periodic Table
Group numbers are used to categorize the vertical columns in the periodic table. Each group contains elements with similar chemical and physical properties due to their identical number of valence electrons.
There are 18 groups in the modern periodic table, numbered from 1 to 18. These groups help in predicting the chemical behavior and bonding tendencies of elements.
Significance of Group Numbers
- Group 1: Alkali Metals (e.g., Li, Na, K) – 1 valence electron
- Group 2: Alkaline Earth Metals (e.g., Mg, Ca) – 2 valence electrons
- Groups 3–12: Transition Metals – variable valence electrons
- Group 17: Halogens (e.g., Cl, F) – 7 valence electrons
- Group 18: Noble Gases (e.g., He, Ne, Ar) – 8 valence electrons (except Helium)
Valence Electrons and Reactivity
Elements in the same group share the same number of valence electrons. This determines their chemical reactivity. For instance, alkali metals are extremely reactive because they easily lose one valence electron, while noble gases are inert due to a full valence shell.
Group Naming Conventions
There are two common systems for naming groups:
- IUPAC System: Uses numbers 1–18 (international standard)
- Old Notation: Uses Roman numerals and A/B (e.g., IA, IIA, IIIB)
Example: Carbon (C) belongs to Group 14 and has 4 valence electrons. This is why it can form four covalent bonds.
Trends Within Groups
As you move down a group:
- Atomic size increases
- Ionization energy decreases
- Reactivity of metals increases