Chemistry - Trends in the Periodic Table

Atomic Radius

half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond

Increase

values of the atomic radius ____ down the groups in the Periodic Table

Reasons for Increasing Atomic Radius

• new energy level

• screening effect of inner electrons

Screening Effect

the electrons in the inner energy level or levels helps to shield the outer electrons from the positive charge of the nucleus

Decrease

values of the atomic radius _____ across a period in the Periodic Table

Reasons for Decreasing Atomic Radius

• increase in effective nuclear charge

• no increase in the screening effect

First Ionisation Energy

the minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state

Decrease

values of the first ionisation energy _____ down a group in the Period Table

Reasons for Decreasing First Ionisation Energy

• increasing atomic radius

• screening effect of inner electrons

• (same as for electronegativity)

Increase

values of the first ionisation energy _____ across a period in the Periodic Table

Reasons for Increasing First Ionisation Energy

• increasing effective nuclear charge

• decreasing atomic radius

• (same as for electronegativity)

Second Ionisation Energy

the energy required to remove an electron from an ion with one positive charge in the gaseous state

Electronegativity

the relative attraction an atom in a molecule has for the shared pair of electrons in a covalent bond

Decrease

values of electronegativity _____ down the groups in the Periodic Table

Reasons for Decreasing Electronegativity

• increasing atomic radius

• screening effect of inner electrons

• (same as for first ionisation energy)

Increase

values of electronegativity _____ across the periods in the Periodic Table

Reasons for Increasing Electronegativity

• increasing effective nuclear charge

• decreasing atomic radius

• (same as for first ionisation energy)

Chemical Reactivity of Alkali Metals

• reactivity of the alkali metals increases down the group

• very reactive, low first ionisation energy

• none of them occur free in nature as metal

• readily form ionic compounds (low electronegativity and first ionisation energy)

Oxide

forms when an alkali metal reacts with oxygen

Hydroxide

forms when an alkali metal reacts with water

Chemical Reactivity of Halogens

• most electronegative elements

• fluorine is the most electronegative

• do not exist free in nature

• remove electrons easily from other substances (oxidising agents)

• boiling points increase down the group (stronger van der Waals forces)