Trends down a group reading

Chemical properties are determined by their electron configuration thus elements in the same groups ( same valence electrons ) have similar chemical properties.

Group 18 ( Noble Gases )

• Colourless gases

• Monatomic ( Exist as single atoms )

• Very unreactive

  • Due to inability to gain/lose electrons

• Generally unable to form positive/Negative ions

  • Not positive since highest ionization energies

  • Not negative since extra electrons must go to outer shell where the nuclear force is negligible

Group 1 ( Alkaline Metals )

Physical Properties	Chemical Properties
Good conductors of electricity ( bc of outer electron )	Highly reactive; cannot exist in nature
Shiny grey when cut	form ionic compounds with non-metals
Low Densities

Group 17 ( Halogens )

Exist as Diatomic Atoms $(X_2)$

Physical Properties	Chemical Properties
Coloured	Very reactive non-metals; reactivity decreases down the group
Gradual change from gases ($F_2$and $Cl_2)$, to liquid ( $Br_2$), and solids ( $I_2$ and $At_2$) Yellow --> Green --> Red --> Red/purple --> Black	Form ionic compounds w/ metals and covalent compounds w/ nonmetals

The reactivity is explained from the almost full electron shell.

Halogens+ Alkaline metals = Halides.

Melting Points

Much more complex as it depends on both on the type of bonding and structure

Element	Melting Point / K	Element ( 17 )	Melting Point / K
Li	454	$F_2$	54
Na	371	$Cl_2$	172
K	337	$Br_2$	266
Rb	312	$I_2$	387
Cs	302	$At_2$	575

From such we can conclude:

• Halogens' MP increases going down a group.

• Alkaline Metals decrease going down a group.