Select three elements from the first 20 and provide their atomic numbers, electron arrangements, and identify an alkali metal, halogen, and noble gas with one property each.

TASK 1: PRACTICAL - ATOMIC STRUCTURE AND PERIODICITY

a) Select any three elements from the first 20 elements and:

i) Write their atomic numbers.

• Hydrogen (H): Atomic number = 1
• Carbon (C): Atomic number = 6
• Oxygen (O): Atomic number = 8

ii) Write their electron arrangement using s and p orbitals.

• Hydrogen (H): $1s^1$
• Carbon (C): $1s^2 2s^2 2p^2$
• Oxygen (O): $1s^2 2s^2 2p^4$

b) Identify one alkali metal, one halogen and one noble gas from the first 20 elements and state one property of each.

| Category | Example | Property | | :---------- | :---------- | 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