State why the atomic weight of an element is also termed - relative atomic mass.

State how electrons are distributed in an atom. Explain in brief the rules which govern their distribution.

Draw the atomic diagrams of the following elements showing the distribution of - protons, neutrons & the electrons in the various shells of the atoms.

(a) Carbon - ¹²₆C

(b) Oxygen - ¹⁶₈O

(c) Phosphorus - ³¹₁₅P

(d) Argon - ⁴⁰₁₈Ar

(e) Calcium - ⁴⁰₂₀Ca

[The upper number represents the - mass number & the lower number the - atomic number e.g. calcium - mass number = 40, atomic number = 20]

'Valency' is the number of hydrogen atoms which can combine with [or displace] one atom of the element [or radical] forming a compound. With reference to the above definition of valency, state the valency of chlorine in hydrogen chloride, giving reasons.