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Revision:Periodicity - 03

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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Periodicity - 03

3.1 The Periodic Table

3.1.1

Elements increase in atomic number across each period, and down each group. The history is boring and pointless (like all history) - ignore it.

3.1.2

Group - the columns going down.

Period - the rows going across.

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.

3.2 Physical Properties

3.2.1

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 --> decreased forces.

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

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.

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 ie P4, S8). Drops to Cl, due to smaller molecules (Cl2) decreases to Ar (individual atoms --> fewer electrons --> smaller LDF).

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

3.3 Chemical Properties

3.3.1

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

Alkali metal (group 1) with water:

$\mathsf{2Na + 2H_2O \longrightarrow 2Na^+ + 2OH^- + H_2}$

Alkali metal (group 1) with Halogen:

$\mathsf{2Na + Cl_2 ---heat---> 2NaCl}$

(Na acts as a reducing agent - is oxidized, Cl₂ is reduced)

Halogen with water:

$\mathsf{Cl_2 + H_2O \leftrightarrows HCl + HClO}$

(Exception F₂ is such a strong oxidizer : $/\mathsf{2F_2 + 2H_2O \longrightarrow 4HF + O_2}$ )

Halogen + Halide ion

Halogen	Cl-	Br-	I-
Cl₂	Colorless --> Cl₂	Red --> Br₂	Violet --> I₂
Br₂	Red --> Br₂	Red --> Br₂	Violet --> I₂
I₂	Violet --> I₂	Violet --> I₂	Violet --> I₂

Halide ion with Silver ion

$\mathsf{Ag^+ + Cl^- \longrightarrow AgCl_{(s)}}$ (a white precipitate)

$\mathsf{Ag^+ + Br^- \longrightarrow AgBr_{(s)}}$ (a cream precipitate)

$\mathsf{Ag^+ + I^- \longrightarrow AgI_{(s)}}$ (a yellow precipitate)

3.3.2

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

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

Oxide	Adding H₂O	Adding HCl	Adding NaOH	Nature
Na₂O	$\mathsf{Na_2O + H_2O \longrightarrow}$ $\mathsf{2NaOH}$	$\mathsf{Na_2O + H^+ \longrightarrow}$ $\mathsf{2Na^+ + H_2O}$	No reaction	Basic Oxide
MgO	$\mathsf{MgO + H_2O \longrightarrow}$ $\mathsf{Mg(OH)_2}$	$\mathsf{MgO + 2H^+ \longrightarrow}$ $\mathsf{Mg^{2+} + H_2O}$	No reaction	Basic Oxide
Al₂O₃	Insoluble	$\mathsf{Al_2O_3 + 6H^+ \longrightarrow}$ $\mathsf{2Al^{3+} + 3H_2O}$	$\mathsf{Al_2O_3 + 2OH^- + 3H_2O}$ $\mathsf{\longrightarrow 2Al(OH)_4}$	Amphoteric Oxide
SiO₂	Insoluble	No reaction	$\mathsf{SiO_2 + 2OH^- \longrightarrow}$ $\mathsf{SiO_3^{2-} + H_2O}$	Acidic Oxide
P₄O₁₀ (or P₄O₆)	$\mathsf{P_4O_{10} + 6H_2O \longrightarrow}$ $\mathsf{4H_3PO_4}$	No reaction	$\mathsf{P_4O_{10} + 12OH^- \longrightarrow}$ $\mathsf{4PO_4^{3-} + 6H_2O}$	Acidic Oxide
SO₃ (or SO₂)	$\mathsf{SO_3 + H_2O \longrightarrow}$ $\mathsf{H_2SO_4}$	No reaction	$\mathsf{SO_3 + OH^- \longrightarrow}$ $\mathsf{SO_4^{2-} + H_2O}$	Acidic Oxide
Cl₂O₇	$\mathsf{Cl_2O_7 + H_2O \longrightarrow}$ $\mathsf{HClO_4}$	No reaction	$\mathsf{Cl_2O_7 + OH^- \longrightarrow}$ $\mathsf{2ClO_4^- + H_2O}$	Acidic Oxide

Halides (assuming Cl - could replace with Br, I, F etc): Ionic Chlorides --> dissolved in H₂O with little reaction, Covalent Chlorides --> dissolve + react to form HCl.

$\mathsf{NaCl: NaCl + H_2O \longrightarrow Na^+ + Cl^- + H_2O}$

$\mathsf{MgCl_2: MgCl_2 \longrightarrow Mg^{2+} + 2Cl^-}$

$\mathsf{Al_2Cl_6: Al_2Cl_6 + 6H_2O \longrightarrow 2Al(OH)_3 + 6HCl}$

This isn't required....not like it's hard $\mathsf{SiCl_4: SiCl_4 + H_2O \longrightarrow Si(OH)_4 + 4HCl}$

$\mathsf{PCl_3: PCl_3 + 3H_2O \longrightarrow H3PO_3 + 3HCl}$

$\mathsf{S_2Cl_2: 2S_2Cl_2 + 2H_2O \longrightarrow 3S + SO_2 + 4HCl}$

$\mathsf{Cl_2: Cl_2 + H_2O \longrightarrow HCl + HClO}$ (Exception : F2 is such a strong oxidizer: $\mathsf{2F_2 + 2H_2O \longrightarrow 4HF + O_2}$ )