The electronic configuration of an atom provides several key pieces of information about its structure and chemical behaviour. From the arrangement of electrons in shells and subshells, we can determine the element's group, period, valency, number of valence electrons, chemical nature (metal, non-metal, or metalloid), and the type of bonds it is likely to form.
Electronic configuration reveals the number of shells (period) and valence electrons (group).
Number of occupied shells = period of the element.
Valence electrons ≤ 4: valency equals the number of valence electrons.
Valence electrons > 4: valency = 8 minus the number of valence electrons.
1–3 valence electrons → metal; 5–7 valence electrons → non-metal.
8 valence electrons → noble gas (chemically inert, valency = 0).
Electronic configuration determines whether an atom forms ionic or covalent bonds.
Na (2,8,1) → Period 3, Group 1, Valency 1, Metal.
Electronic configuration tells us:
Number of shells occupied — indicates the period (row in periodic table) Example: 2,8,1 has 3 shells → Period 3
Number of valence electrons — electrons in the outermost shell Example: 2,8,1 has 1 valence electron
Group of the element — based on valence electrons Elements with 1 valence electron → Group 1 (Alkali metals) Elements with 7 valence electrons → Group 17 (Halogens) Elements with 8 valence electrons → Group 18 (Noble gases)
Valency — combining capacity of the atom If valence electrons ≤ 4: Valency = number of valence electrons If valence electrons > 4: Valency = 8 − (number of valence electrons)
Chemical nature (metal, non-metal, metalloid) 1–3 valence electrons: metals (tend to lose electrons) 5–7 valence electrons: non-metals (tend to gain electrons) 4 valence electrons: metalloids (e.g., Si, Ge)
Period: • Count the number of occupied electron shells. • That number is the period.
Examples: • Na: 2,8,1 → 3 shells → Period 3 • Cl: 2,8,7 → 3 shells → Period 3 • Ca: 2,8,8,2 → 4 shells → Period 4
Group (for s and p block elements): • 1 valence electron → Group 1 • 2 valence electrons → Group 2 • 3 valence electrons → Group 13 • 4 valence electrons → Group 14 • 5 valence electrons → Group 15 • 6 valence electrons → Group 16 • 7 valence electrons → Group 17 • 8 valence electrons → Group 18 (noble gases)
Valency is the combining capacity of an atom:
For elements with valence electrons 1 to 4: Valency = number of valence electrons
For elements with valence electrons 5 to 7: Valency = 8 − valence electrons
For noble gases (8 valence electrons): Valency = 0
Examples: • Na (2,8,1) → 1 valence electron → Valency = 1 • Mg (2,8,2) → 2 valence electrons → Valency = 2 • Al (2,8,3) → 3 valence electrons → Valency = 3 • C (2,4) → 4 valence electrons → Valency = 4 • N (2,5) → 5 valence electrons → Valency = 8−5 = 3 • O (2,6) → 6 valence electrons → Valency = 8−6 = 2 • Cl (2,8,7) → 7 valence electrons → Valency = 8−7 = 1 • Ar (2,8,8) → 8 valence electrons → Valency = 0
Electronic configuration also reveals:
Metallic or non-metallic character: • 1–3 valence electrons → metallic (tends to lose electrons, forms cations) • 5–7 valence electrons → non-metallic (tends to gain electrons, forms anions) • 4 valence electrons → can be either (e.g., C forms covalent bonds)
Type of bond formed: • Metals + non-metals → ionic bond (transfer of electrons) • Non-metals + non-metals → covalent bond (sharing of electrons)
Stability: • Atoms with completely filled shells (like noble gases with 8 valence electrons) are chemically stable and unreactive. • Atoms try to achieve noble gas configuration by gaining, losing, or sharing electrons.
Oxidation state: • Can be predicted from the number of electrons an atom tends to lose or gain.
Electronic configuration provides: (1) Period — number of electron shells occupied; (2) Group — based on number of valence electrons; (3) Valency — combining capacity; (4) Chemical nature — metal, non-metal, or metalloid; (5) Type of bonding — ionic or covalent; (6) Chemical reactivity and stability.
The period equals the number of electron shells occupied. Example: Na has configuration 2,8,1 — three shells are occupied, so Na is in Period 3. Ca has configuration 2,8,8,2 — four shells, so Ca is in Period 4.
If valence electrons ≤ 4: valency = number of valence electrons. If valence electrons > 4: valency = 8 − valence electrons. Example: Cl (2,8,7) has 7 valence electrons → Valency = 8−7 = 1. Na (2,8,1) has 1 valence electron → Valency = 1.
Atoms with 1–3 valence electrons tend to lose electrons → metals. Atoms with 5–7 valence electrons tend to gain electrons → non-metals. Atoms with 4 valence electrons can form covalent bonds (e.g., carbon). Noble gases with 8 valence electrons are inert.
An atom with 8 valence electrons (completely filled outer shell) is a noble gas. It is chemically stable and unreactive, with valency = 0. Examples: He (2), Ne (2,8), Ar (2,8,8), Kr (2,8,18,8). Other atoms try to achieve this stable configuration.
Molar Mass of HNO3 (Nitric Acid)
Learn how to calculate the molar mass (molecular weight) of HNO3 (Nitric Acid) step-by-step. Find out atomic masses of Hydrogen, Nitrogen, and Oxygen.
How to Find or Calculate Valency
Learn how to easily calculate the valency of an element using its atomic number and electronic configuration. A simple guide for Class 9 chemistry students.
What is the Full Form of HSD? (Fuel & Engineering)
Learn the full form of HSD (High Speed Diesel) in petroleum engineering. Understand the massive difference between HSD and LDO (Light Diesel Oil) fuels.
Hybridization Definition in Chemistry
Learn the definition of Hybridization in chemistry. Understand how atomic orbitals mix to form hybrid orbitals with identical shapes and energies.
What is Hydration Enthalpy?
Learn the definition of hydration enthalpy. Understand why it is always negative, its relationship with ionic charge and size, and its trend in the periodic table.
Turn this guide into revision flashcards, a practice exam, or an AI-generated podcast — free, no signup required.