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. *Mendeleev turns in his grave*

[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. The outer electron is in an energy level that is progressively further away away from the centre of the nucleus.

'Ionic radius decreases'? due to the fact the valence electron has been removed from the outer shell. This allows the protons within the nucleus to have a greater attraction towards the electrons because there is now one extra proton more compared to the amount of electrons. There is also one fewer energy level, because the outer shell has effectively been removed.'

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