Essential Concepts in Atomic Physics and Chemistry

Atomic Magnitudes

Atomic magnitudes characterize an atom. An atom consists of three fundamental particles: protons, electrons, and neutrons.

Atomic Number (Z)

The atomic number indicates the number of protons and defines an element's position in the periodic table. In a neutral atom, it is equal to the number of electrons.

Mass Number (A)

The mass number represents the total number of nucleons (protons and neutrons) found in the nucleus.

Quantum Numbers

• n = 1, 2, 3...
• l = 0, 1... (n-1)
• m = -l... 0... +l
• s = +1/2, -1/2

Electronic Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴ 6d¹⁰ 7p⁶

Quantum Number Exercises

• a) (3, 2, -2, +1/2): Possible; values are within accepted ranges.
• b) (4, 0, 1, +1/2): Not possible; if the secondary quantum number (l) is 0, m must also be 0.
• c) (2, 2, 1, -1/2): Not possible; if the principal quantum number (n) is 2, the secondary quantum number (l) must be 0 or 1.
• d) (2, -1, 0, 0): Not possible; the spin (s) must be ±1/2, and the secondary quantum number cannot be negative.

Chemical Bonding

Covalent Bond

Formed when atoms share electron pairs to achieve a noble gas configuration. This typically occurs between non-metals or non-metals with hydrogen.

• Nonpolar Covalent Bond: Occurs between identical atoms with equal electronegativity, keeping the electron pair centered.
• Double Covalent Bond: Two pairs of electrons are shared.
• Triple Covalent Bond: Three pairs of electrons are shared.

Ionic Bond

Formed by the transfer of electrons from a metal to a non-metal. The metal becomes a cation, and the non-metal becomes an anion, held together by electrostatic attraction.

Periodic Trends Example

Z = 38: Located in the 5th period. Valence shell is 5s² (Group 2, Alkaline Earth Metals).

Z = 52: Located in the 5th period. Valence shell is 5s² 5p⁴ (Group 16, Chalcogens).

Trends: Atomic radius decreases as Z increases due to higher nuclear attraction. Consequently, Z = 52 has a smaller radius, higher ionization energy, higher electron affinity, and higher electronegativity compared to Z = 38.