Group properties
Alkali metals (only lithium, sodium and potassium for IGCSE): Physical properties:
-Good conductors of heat and electricity.
-Are soft, compared to other metals.
-They have low densities (for metals).
-They have low melting and boiling points compared to most metals. Chemical properties:
-Form ionic compounds
-React violently with chlorine
-Burst into flames when heated with oxygen:
-a red flame for lithium
-a yellow flame for sodium
-a lilac flame for potassium
-Produce soluble white compounds.
-React with cold water.
Patterns: Reactivity, density and softness increases further down the group i.e. Caesium is more reactive that lithium. Melting and boiling points decrease. Reactivity increases because more electron shells means there is a less strong attraction between the nucleus and the valency electron so it is lost more easily.
Halogens, group 7 – physical properties:
-form coloured gases (at room temperature, fluorine is a yellow gas, chlorine is a green gas, bromine is a red liquid, and iodine is a black solid)
-are poisonous
-are brittle and crumbly in solid form
-do not conduct electricity
-form diatomic molecules
Patterns: (down the group) size, mass and density increase (and colour darkness). Reactivity decreases, because it has to gain an electron, so the closer the electron is to the positive nucleus the more easily it will be gained, so atoms with fewer shells will react more easily.