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Inorganic chemistry

Organization of the periodic table | Trends within group 1 & 2 | Group7 (Halogens) | Other pages

Organization of the periodic table

All the known elements so far are listed on the periodic table.
They are arranged in periods (horizontal rows) and groups (vertical columns)

periodic table periods and groups

Here are the factors that changes as moving across a period or going down a group.

Period Group

Atomic radius Decreases across a period Increases down a group

Ionic radius Decreases across a period Increases down a group

Electronegativity Increases across a period Decreases down a group

Note: Ionic radius can be cationic or anionic. When an atom becomes an ion, if it is a cationic, the ionic radius is smaller than its atomic radius. If it is an anionic, the Ionic radius is larger than its atomic radius.
Here are the examples:

The radius of Mg⁺² (cation) is smaller than Mg (atom).
The radius of Cl^- (anion) is bigger than Cl (atom).

and here are the ionic radius examples

Trends within group 1 & 2

These are the most commonly made comparisons between group1 and group2.

Atomic radius Reactivity Hardness Thermal stability

Increase Increase as going down each group Increase as going down each group Increase as going across group1 to group2 Group1 compounds are more thermal stable than group 2

Decrease Decreases as going across group1 to group2 Decreases compare group2 element to group1 element within the same period Decreases as going down each group Group2 compounds are less thermal stable than group1 compounds

Ionization

Group1 and 2 elements are metals. Metals undergo redox reaction and they become cation when ionized.

check out redox reaction

Solubility of group1 and group2 ionic compounds

Lattice energy and hydration energy have to be considered when discussing the solubility of ionic compounds.
Lattice energy determines the strength of ionic compounds.
Hydration energy is when an ionic compound is dissolved in water, the force (attraction) of water molecules that try to break the ionic compound.
These two kinds of energy vary according to the size of cations and anions that form a substance.
Let's take group2 elements as cation and sulphate (large anion) and hydroxide (small anion) as anions.

Group2 ions & Sulphate ion (SO₄^2-) Group2 ions & Hydroxide ion (OH^-)

Lattice energy As descending the group2, the size of cation increases and this will cause to weak the ionic bonding. However, because the SO₄^2- anion is very large so the size of cation doesn't affect the lattice energy. As descending the group 2, the size of cation increases. This causes to push OH^- anion away and result to decrease the lattice energy. (descending group2 increases solubility)

Hydration energy Hydration energy decreases (becomes smaller) as the size of cation (group2) increases. Hydration energy decreases (becomes smaller) as the size of cation increases. In this case decrease in lattice energy is faster than hydration energy, this is why hydroxide compounds are more soluble than sulphite compounds.

Solubility Therefore hydroxide compounds are more soluble than sulphate compounds.

Actual solubility of each compound (unit =100 times the mass of anhydrous solute per unit mass of water)
OH^- SO₄^2-

Be²⁺ sparingly soluble 39

Mg²⁺ 0.0009 33

Ca²⁺ 0.156 0.21

Sr²⁺ 0.80 0.013

Ba²⁺ 3.9 0.00024

**Actual solubility of each compound**
	OH^-	SO₄^2-
Be²⁺	sparingly soluble	39
Mg²⁺	0.0009	33
Ca²⁺	0.156	0.21
Sr²⁺	0.80	0.013
Ba²⁺	3.9	0.00024

Group7 (Halogens)

Name	Symbol	Colour	State	Intermolecular force
Fluorine	F	Pale yellow	Gas	Increase in vander waals force
Chlorine	Cl	Yellow green	Gas
Bromine	Br	Red-Brown	Liquid
Iodine	I	Black	Solid

Note:Fluorine has weaker covalent bonding than chlorine or even bromine!!!
This is because fluorine atoms are small with a lot of electrons on its outershell (electrons repel each other).

Ionization

Halogens (group 7 elements) are oxidizing agents. Fluorine is the most powerful oxidizing agent.
THe strength of oxidizing agent can be tested by displacement reaction.

For example: Cl₂ _(aq) + 2Br ^- _(aq) ® 2Cl^- _(aq) + Br₂ _(aq)
However: Br₂ _(g) + 2Cl^- _(aq) ® No reaction

Therefore Cl₂ is stronger B agent than Br₂

Reactions with halogens

Disproportionation: Simultaneous oxidation and reduction of the same element in a reaction.
When chlorine, bromine and iodine react with water, disproportionation occurs. Disproportionation of chlorine

Note: green numbers are oxidation number

Other reactions
I only listed the ones that I found quite tricky.

Halogens ( I₂: weak Simultaneous agent/ Cl₂: strong Simultaneous agent ) with thiosulphate (S₂O₃^2- )

Contents & give your comment

Structure and Bonding

	Period	Group
Atomic radius	Decreases across a period	Increases down a group
Ionic radius	Decreases across a period	Increases down a group
Electronegativity	Increases across a period	Decreases down a group

	Atomic radius	Reactivity	Hardness	Thermal stability
Increase	Increase as going down each group	Increase as going down each group	Increase as going across group1 to group2	Group1 compounds are more thermal stable than group 2
Decrease	Decreases as going across group1 to group2	Decreases compare group2 element to group1 element within the same period	Decreases as going down each group	Group2 compounds are less thermal stable than group1 compounds

	Group2 ions & Sulphate ion (SO₄^2-)	Group2 ions & Hydroxide ion (OH^-)
Lattice energy	As descending the group2, the size of cation increases and this will cause to weak the ionic bonding. However, because the SO₄^2- anion is very large so the size of cation doesn't affect the lattice energy.	As descending the group 2, the size of cation increases. This causes to push OH^- anion away and result to decrease the lattice energy. (descending group2 increases solubility)
Hydration energy	Hydration energy decreases (becomes smaller) as the size of cation (group2) increases.	Hydration energy decreases (becomes smaller) as the size of cation increases. In this case decrease in lattice energy is faster than hydration energy, this is why hydroxide compounds are more soluble than sulphite compounds.
Solubility	Therefore hydroxide compounds are more soluble than sulphate compounds.