The Periodic Table

The Periodic Table

• The Periodic Table is a chart that categorises chemical elements based on their atomic structure and properties.
• The current form of the Periodic Table is the Modern Periodic Table, organised by Dimitri Mendeleev and Lothar Meyer in the late 19th century.
• Elements are placed from left to right and top to bottom in order of increasing atomic number.
• The vertical columns are called groups, and the horizontal rows are called periods.

Groups in the Periodic Table

• Elements in the same group share similar chemical properties because they have the same number of valence electrons in their outer shell.
• These electron configurations explain the trend in reactivity within the groups.
• The periodic table consists of eight groups numbered from group 1 (alkali metals) to group 0 (noble gases).
• The noble gases (group 0), being the rightmost group, are chemically unreactive as they have full outer shells.

Periods in the Periodic Table

• As you move across a period from left to right, the number of protons increases, and so does the number of electrons.
• Elements in the same period have the same number of atomic orbitals or energy levels.
• The properties of elements change across a period, transitioning from metallic (left side) to non-metallic (right side) characteristics.

Blocks of the Periodic Table

• The Periodic Table is divided into blocks (s, p, d, and f) based on the sublevel being filled in the electron configuration.
• The s-block includes alkali and alkaline earth metals and hydrogen and helium.
• The p-block includes groups 3-0.
• The d-block is the transition metals.
• The f-block consists of the lanthanides and actinides, often placed separately below the main table.

Trends in the Periodic Table

• Trends across periods and down groups include changes in atomic radius, ionisation energy, electronegativity, and reactivity.
• For example, reactivity increases as you go down group 1 (alkali metals) and decreases as you go down group 7 (halogens).
• The reason for these trends is the increasing number of energy levels and other factors like the number of protons or electron shielding.

Alkali Metals (Group 1) and Halogens (Group 7)

• The alkali metals are very reactive and are stored under oil to prevent reaction with air or water.
• Reactions of alkali metals with water produce an alkaline metal hydroxide and hydrogen gas.
• Halogens are non-metals with coloured vapours. They exist as diatomic molecules, for example, Cl2.
• The halogens become less reactive and more metallic as you move down the group. This can be seen in chemical reactions, such as displacement reactions between halogens and halide salts.