What is the electronic configuration of sodium?

Sodium (Na) has atomic number 11. Electronic configuration: K shell = 2, L shell = 8, M shell = 1, written as (2,8,1). The outermost shell (M) has 1 electron, so valency of sodium = 1.

What are isotopes and isobars?

Isotopes: atoms of the same element with same atomic number (Z) but different mass numbers (A) — e.g., ¹²C and ¹⁴C (Z=6 for both). Isobars: atoms of different elements with different Z but same A — e.g., ⁴⁰Ca (Z=20) and ⁴⁰Ar (Z=18).

How do you find the number of neutrons in an atom?

Neutrons = Mass Number (A) − Atomic Number (Z). Example: Sodium has A=23, Z=11, so neutrons = 23 − 11 = 12. Always look up or remember: Atomic number = protons; Mass number = protons + neutrons.

Bohr Model of Atom

Structure of the Atom • Class 9 Science • NCERT • CBSE

Bohr's model proposed that electrons revolve in fixed circular paths called shells or orbits around the nucleus. Each shell can hold a maximum number of electrons given by the formula 2n², where n is the shell number.

Key Formulas

Maximum electrons in shell n = 2n²
Mass Number (A) = Protons + Neutrons
Neutrons = A − Z (Mass number − Atomic number)
Valency = outermost electrons (if ≤ 4) or 8 − outermost electrons (if > 4)

Frequently Asked Questions

What is the electronic configuration of sodium?: Sodium (Na) has atomic number 11. Electronic configuration: K shell = 2, L shell = 8, M shell = 1, written as (2,8,1). The outermost shell (M) has 1 electron, so valency of sodium = 1.
What are isotopes and isobars?: Isotopes: atoms of the same element with same atomic number (Z) but different mass numbers (A) — e.g., ¹²C and ¹⁴C (Z=6 for both). Isobars: atoms of different elements with different Z but same A — e.g., ⁴⁰Ca (Z=20) and ⁴⁰Ar (Z=18).
How do you find the number of neutrons in an atom?: Neutrons = Mass Number (A) − Atomic Number (Z). Example: Sodium has A=23, Z=11, so neutrons = 23 − 11 = 12. Always look up or remember: Atomic number = protons; Mass number = protons + neutrons.

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