The Periodic Table

1. General Structure

Periodic Table

Proton Number: Elements are arranged in order of increasing proton number.
Periods: Horizontal rows.
Groups: Vertical columns.
Periodicity: Elements in the same group have similar chemical properties because they have the same number of valence electrons.

Character: Transition from metallic character (left) to non-metallic character (right).
Ion Charge: Group number relates to the charge of the ion formed to achieve a noble gas configuration.

Elements: Lithium (Li), Sodium (Na), Potassium (K), etc.
Physical Properties: Relatively soft, low density.
Trends (Down the Group):
- Melting Point: Decreases.
- Density: Increases.
- Reactivity: Increases (outer electron is further from nucleus, easier to lose).

Elements: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I).
General Nature: Diatomic non-metals ($\text{F}_2, \text{Cl}_2, \text{Br}_2, \text{I}_2$).
Appearance:
- $\text{Cl}_2$: Pale yellow-green gas.
- $\text{Br}_2$: Red-brown liquid.
- $\text{I}_2$: Grey-black solid.
Trends (Down the Group):
- Density: Increases.
- Reactivity: Decreases (harder to attract/gain an electron as shell number increases).
Displacement Reactions: A more reactive halogen will displace a less reactive halogen from its salt.
- Example: $\text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2$

Location: Middle block of the Periodic Table.
Properties:
- High density.
- High melting points.
- Form coloured compounds.
- Often act as catalysts (e.g., Fe in Haber process).
- Often exhibit variable oxidation numbers (e.g., $\text{Fe}^{2+}$ and $\text{Fe}^{3+}$).

Elements: Helium (He), Neon (Ne), Argon (Ar), etc.
General Nature: Monatomic gases.
Reactivity: Very unreactive (inert) because they have full outer electron shells.

To identify group trends from provided data, look for consistent increases or decreases in physical or chemical properties (e.g., boiling point, atomic radius, ionization energy) as the atomic number increases within a group.