The periodic Table
Groups
A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying
the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group.
These groups tend to be given names, e.g., the alkali metals, alkaline metals, halogens and noble gases.
Periods
A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are
some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical
group trends. This can be true in the transition metals.
Comparison of groups in the periodic table
Alkali Metals
Transition Metals
Halogens
Noble gasses
Low (Li, K and Na float in
water). Soft (can be cut
with a knife)
High; usually hard and
tough; can be hammered or
bent into shape
Low
(brittle when solid)
Low
Ability to
conduct heat
and electricity
Good
Good
(metalloids semiconductors)
Poor
Poor
Melting point
Low
High
(mercury is exception)
Low
Very low
React quickly with water
producing hydrogen gas
Less reactive than alkali
metals such as Li, Na, K.
Highly reactive
Stable/unreactive
Become softer, denser and
more reactive; melting
point decreases
Not significant
Become darker and less
reactive; melting point
increases
Density increases
Density
Reactivity
Trends in the
Periodic table
(Going down)