The Periodic Table (Edexcel A Level Chemistry): Flashcards

Periodicity is the repeating pattern of chemical and physical properties observed across each period of the Periodic Table.

Elements are arranged in order of increasing atomic number, and properties such as ionisation energy and melting point repeat in a predictable pattern.

Melting point increases from sodium to aluminium because the strength of metallic bonding increases. Each element donates more electrons to the delocalised sea (Na donates 1, Mg donates 2, Al donates 3), creating stronger electrostatic attraction between the positive ions and the delocalised electrons.

After silicon, the elements (P, S, Cl, Ar) are simple molecular substances. The covalent bonds within molecules are strong, but the intermolecular forces between molecules are weak instantaneous dipole-induced dipole forces. Little energy is needed to overcome these, so melting points are low.

False.

Silicon has the highest melting point in Period 3 because of its giant covalent structure, in which each silicon atom is bonded to neighbouring silicon atoms by strong covalent bonds. Silicon is a non-metal and does not have metallic bonding.

Across a period, atomic radius decreases because nuclear charge increases while shielding remains roughly constant, pulling outer electrons closer to the nucleus.

There is a dip in first ionisation energy between magnesium and aluminium because aluminium's outer electron is in the 3p subshell, which is at a higher energy level and further from the nucleus than the 3s subshell of magnesium. It is therefore easier to remove.

True.

Sulfur has two electrons paired in the 3p_x orbital. The spin-pair repulsion between these electrons makes one of them slightly easier to remove, giving sulfur a lower first ionisation energy than phosphorus despite the higher nuclear charge.

First ionisation energy generally increases across a period because nuclear charge increases while the shielding by inner electrons remains roughly constant.

First ionisation energy shows a large decrease between the last element of one period and the first of the next. This is because a new electron shell is added, increasing both the distance from the nucleus and the shielding by inner electrons. These effects outweigh the increased nuclear charge.