A. The number of valence electrons increases as atomic mass increases. == Generally true for the representative elements since atomic mass generally increases with increasing Z.
B. The reactivity of alkali metals increases as atomic mass increases. == True. Atomic mass increases down the column and so does reactivity
C. The reactivity of the halogens increases as atomic mass increases. == False. Reactivity decreases down the column.
D. The number of valence electrons decreases across a period. == False. In general, the number of valence electrons increases across a period, particularly for the representative elements.
Given molecule Lithium iodide (LiI)
Heat of hydration = -793 kj/mol
Lattice energy = -730 kJ/mol
Heat of hydration = Heat of solution - Lattice energy
Heat of solution = Hydration + Lattice = -793 + (- 730) = -1523 kJ/mol
Now,
Mass of LiI = 15.0 g
molar mass of LiI = 134 g/mol
# moles of LiI = 15/134 = 0.112 moles
Heat of solution for 1 mole of LiI = -1523 KJ
Therefore, for 0.112 moles of LiI the corresponding heat is
= 0.112 *(-1532) = 171.6 kJ
Valence electrons are shared in covalent bonds
Half reaction 1: 2Fe° → Fe₂³⁺ + 6e⁻ /×2.
4Fe° → 2Fe₂³⁺ + 12e⁻.
Iron is oxidized from neutral charge (0) to oxidation number +3, one iron lose three electrons, two irons lose six electrons and four irons twelve electrons.
Half reaction 2: 12e⁻ + 3O₂ → 2O₃²⁻
Oxygen is reduced from neutral chage to oxidation number -2, one oxygen gain two electrons, six oxygens gain twelve electrons.
Balanced chemical reaction: 4Fe + 3O₂ → 2Fe₂O₃.
<em>An atom is called the mass number. </em><em />
