Topic 3 - Periodicity

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[edit] 3.1 The Periodic Table

[edit] 3.1.1

Elements increase in atomic number across each period, and down each group. The history is boring and pointless (but then, I’ve never been much of a history fan) and can probably be ignored.

[edit] 3.1.2

Group – the columns going down.
Period – the rows going across.

[edit] 3.1.3

Group = number of valence electrons in the atom. Period = number of main electron shells…s, p , d and f blocks as described above.

[edit] 3.2 Physical Properties

[edit] 3.2.1

[edit] Li->Cs (down the alkali metals)

Atomic radius increases due to increased electron shielding.

Ionic radius increases due to increased electron shielding.

Ionisation energy decreases due to increased electron shielding.

Melting/boiling point decreases due to increased electron shielding (hence decreased forces).

Electronegativity decreases due to increased shielding (hence decreased attraction for outer electrons).

[edit] F->I (Down the halogens)

Atomic radius increases due to increased electron shielding.

Ionic radius increases due to increased electron shielding.

Ionisation energy decreases due to increased electron shielding.

Melting/boiling point increases due to increased number of electrons->increased london dispersion forces.

Electronegativity decreases due to increased shielding -> decreased attraction for outer electrons.

[edit] Na->Ar (across period 3)

Atomic radius decreases due to increased nuclear charge -> greater attraction for electrons.

Ionic radius decreases Na->Al (due to increased nuclear charge) jumps Al->Si (due to reversal of ionisation direction…increased electron-electron repulsion) decreases Si->Ar (due to increased nuclear charge).

Ionisation energy increases due to increased nuclear charge.

Melting/boiling point increases Na->Si (due to stronger metallic bonding – more delocalized electrons then network covalent) drops Si-P (due to network->molecular covalent) increases P->S (due to increased LDF between molecules i.e. P₄, S₈). Drops to Cl, due to smaller molecules (Cl₂) decreases to Ar (individual atoms->fewer electrons->smaller LDF).

weaker the atom higher the melting point

Electronegativity increases due to increased nuclear charge -> greater attraction for electrons.

[edit] 3.3 Chemical Properties

[edit] 3.3.1

Reactions of elements in the same group are similar because they have identical outer shells (ie same number of valence electrons).

[edit] Generalized reactions

[edit] Alkali metal (group 1) with water

2Na + 2H₂O -> 2Na⁺ + 2OH^- + H₂

[edit] Alkali metal (group 1) with Halogen

2Na + Cl₂ – heat -> 2NaCl (Na acts as a reducing agent, i.e. is oxidized, Cl₂ is reduced)

[edit] Halogen with water

Cl₂ + H₂O <=> HCl + HClO
Exception F₂ is such a strong oxidizer that we get: 2F₂ + 2H₂O -> 4HF + O₂

[edit] Halogen + Halide ion

	Cl^-	Br^-	I^-
Cl₂	Colorless (Cl₂)	Red (Br₂)	Violet (I₂)
Br₂	Red (Br₂)	Red (Br₂)	Violet (I₂)
I₂	Violet (I₂)	Violet (I₂)	Violet (I₂)

[edit] Halide ion with Silver ion

Ag⁺ + Cl^- -> AgCl_(s) (a white precipitate)
Ag⁺ + Br^- -> AgBr_(s) (a cream precipitate)
Ag⁺ + I^- -> AgI_(s) (a yellow precipitate)

[edit] 3.3.2

Elements on the left are metallic, those on the right are non-metals. Al is a metalloid (semi-metal).

Oxides :
Non-metals -> Acidic oxides
Metals -> Basic oxides
Metalloids -> Amphoteric (both acidic & basic) oxides.

	Na₂O	MgO	Al₂O₃	SiO₂	P₄O₁₀ (or P₄O₆)	SO₃ (or SO₂)	Cl₂O₇
Adding H₂O	Na₂O + H₂O -> 2NaOH	MgO + H₂O -> Mg(OH)₂	Insoluble	Insoluble	P₄O₁₀ + 6H₂O -> 4H₃PO₄	SO₃ + H₂O -> H₂SO₄	Cl₂O₇ + H₂O -> HClO₄
Adding HCl	Na₂O + H⁺ -> 2Na⁺ + H₂O	MgO + 2H⁺ -> Mg²⁺ + H₂O	Al₂O₃ + 6H⁺ -> 2Al³⁺ + 3H₂O	No reaction	No reaction	No reaction	No reaction
Adding NaOH	No reaction	No reaction	Al₂O₃ + 2OH^- + 3H₂O -> 2Al(OH)₄	SiO₂ + 2OH^- -> SiO₃^2- + H₂O	P₄O₁₀ + 12OH^- -> 4PO₄^3- + 6H₂O	SO₃ + OH^- -> SO₄^2- + H₂O	Cl₂O₇ + OH^- -> 2ClO₄^- + H₂O
Nature	Basic Oxide	Basic Oxide	Amphoteric Oxide	Acidic Oxide	Acidic Oxide	Acidic Oxide	Acidic Oxide

Halides (assuming Cl, but we could replace it with Br, I, F etc)

Ionic Chlorides -> dissolved in H₂O with little reaction, Covalent Chlorides -> dissolve + react to form HCl.

NaCl : NaCl + H₂O -> Na⁺ + Cl^- + H₂O

MgCl₂ : MgCl₂ -> Mg²⁺ + 2Cl^-

Al₂Cl₆ : Al₂Cl₆ + 6H₂O -> 2Al(OH)₃ + 6HCl

This isn’t required though it’s not like it’s hard
SiCl₄ : SiCl₄ + H₂O -> Si(OH)₄ + 4HCl

PCl₃ : PCl₃ + 3H₂O -> H₃PO₃ + 3HCl

S₂Cl₂ : 2S₂Cl₂ + 2H₂O -> 3S + SO₂ + 4HCl

Cl₂ : Cl₂ + H₂O -> HCl + HClO
(Exception : F₂ is such a strong oxidizer that we get the following : 2F₂ + 2H₂O -> 4HF + O₂)

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Category: IB Chemistry