Chemistry topic 1 IGCSE revision

Aq meaning

In solution

mass number

the total number of protons and neutrons

atomic number

the number of protons

Column

groups

determine reactivity in alkali metals and halogens

Reactivity in alkali metals increases down the group due to increased shielding, reducing attraction to the nucleus; in halogens, reactivity decreases down the group.

what affects the boiling/melting point of the halogens

The intermolecular forces

what affects the boiling/melting point of the alkali metals

size of atom - larger atoms have weaker metallic bonds, leading to lower boiling/melting points.

state the general equation of an alkali metal reacting with water

2M + 2H2O → 2MOH + H2,

where M represents the alkali metal.

how many valence electrons does helium have

Helium has two valence electrons, filling its outer shell and making it a noble gas with stable electronic configuration.

electron mass

1/1840