Periodicity (sl)

3.1	- The Periodic table
3.2	- Physical properties
3.3	- Chemical properties

3.1 - The Periodic Table

A list of the chemical elements arranged into Groups (the columns going down) and Periods (the rows going across). The group number gives the number of valence (outer shell) electrons around the atom. The period number is the same as that of the outer energy shell. Elements increase in atomic number across each period by one.

Example: Calcium is in the 2nd group therefore it has 2 electrons in the outer shell and a valency of +II. It is in the fourth period therefore its outer electrons are in the fourth energy shell.

Trends in physical properties

3.2 - Physical Properties

Characteristic	Trend (left to right)	Reason
Atomic radius	decreases in size from left to right	increased attractive force (acting on the same energy shell) of the nucleus increases as the number of protons increases
Ionic radius	decreases across the period until formation of the negative ions then there is a sudden increase followed by a steady decrease to the end	In general as above. The sudden increase on formation of negative ions is due to the new (larger) outer shell
Electronegativity	Increases	More electron attracting power of the larger nuclear charge as we move to the right
Metallic character	Decreases - Na, Mg, Al metals; Si metalloid; P, S, Cl, Ar non-metals	Metallic character is a measure of the ease of loss of electrons from the outer shell. This decreases with increasing nuclear charge.
Melting point	NaAl steady increase	Increasing availability of electrons in the metallic bonding associated with greater charge density of the metal ion
	Si massive increase	Si giant macromolecular structure
	P large decrease	P₄ molecules
	S small increase	S₈ crown shaped molecules
	Cl Ar decrease	Cl₂ molecules and Ar atoms

The elements of group 1

Characteristic	Trend (descending group 1)	Reason
Atomic radius	increases in size top to bottom	The number of electron shells increases from Li to Cs
Ionic radius	increases from Li to Cs	The number of electron shells increases from Li to Cs
Electronegativity	decreases	Attracting power of the nucleus is sheilded by the inner electron shells increasingly as the group is descended
Ionisation energy	Decreases descending the group	Sheilding effect of the inner electron shells increases as we descend the group and so the outer electron is more easily removed
Melting point	Decreases from Li to Cs	The larger ions have weaker metallic bonding as their charge density (charge/volume ratio)is smaller

The elements of group 7 (Fluorine to Iodine)

Characteristic	Trend (descending group 7)	Reason
Atomic radius	increases in size from F to I	The number of electron shells increases from F to I
Ionic radius	increases from F to I	The number of electron shells increases from F to I
Electronegativity	decreases	Attracting power of the nucleus is sheilded by the inner electron shells increasingly as the group is descended
Ionisation energy	Decreases descending the group	Sheilding effect (repusion caused by the inner electrons) of the inner electron shells increases as we descend the group and so the outer electron is more easily removed
Melting point	Increases from F to I	The larger halogens have greater Van der Waals forces holding the molecules together as they have more electrons

3.3 Chemical Properties

Reactions of elements of the same group are similar because they have identical outer shells (ie same number of valence electrons). The following must be covered:

Reactions of group 1(alkali metals) and group 7 (halogens) elements with water
Reaction of group 1 (alkali metals) elements with group 7 (halogens)
Displacement reaction of halogens
Reaction of silver ions with halide ions (group 7 element ion)
Acidity/basicity of the element oxides
The metallic /non-metallic nature of the elements

Reactions of group 1 and 7

Element	reagent	example equation	conditions (if any)
Group 1(Li...Cs)	water	2Na + 2H₂O --> 2NaOH + H₂	violent reaction
Group 1(Li...Cs)	halogen	2Na + Cl₂ --> 2NaCl	heat needed

Group 7 (halogen)	water	Cl₂ + H₂O HCl + HClO

Displacement reaction of halogens

Reactivity of the halogens decreases going down the group and the more reactive halogen will displace a less reactive halogen from a solution of its ions. This is also a redox reaction.

	Cl^-(aq)	Br^-(aq)	I^-(aq)
Cl₂	Colorless / no reaction	turns red due to formation of bromine	turns brown due to formation of iodine
Br₂	no reaction	no reaction	turns brown due to formation of iodine
I₂	no reaction	no reaction	no reaction

The reactions of Halide ions with Silver ions

	Cl^-(aq)	Br^-(aq)	I^-(aq)
Ag+	white ppt	cream ppt	yellow ppt
reason	insoluble AgCl formed	insoluble AgBr formed	insoluble AgI formed
equation	Ag⁺ + Cl- AgCl	Ag⁺ + Br- AgCl	Ag⁺ + I- AgI

Metallic character of the elements

Elements on the left are metallic...right are non-metals...Si is a metalloid.

Acidic character of the oxides

Metal oxides are basic
Aluminium oxide is amphoteric (reacts with both acids and bases)
Non-metal oxides are acidic

	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

Resources

Ionic and atomic radii

Periodic trends ppt presentation

Atomic and ionic radii display (needs chime)

Useful links

http://www.chem.ox.ac.uk/vrchemistry/periodic_table/Flash/Metallic%20or%20covalent%20basic.swf

Have you tried the Colourful Interactive Solutions for Periodicity Book 3
Animations, explanations, worked past paper type questions and programmable tests.

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