The periodic
table of elements
developed as
chemists tried to
classify the
elements. It
arranges them in
a pattern in
which similar
elements are
grouped
together.
Newlands table
put the
elements in
order of atomic
mass but failed
to take account
of elements that
were unknown
at that time.
Mendeleev's
periodic table left
gaps for the
unknown elements,
and so provided the
basis for modern
periodic table.
C3
1.2
The atomic
(proton)
number of
an element
determines
its place in
the periodic
table
the number of
electrons in the
outer shell
(highest energy
level) of an atom
determines its
chemical
properties
the group
number in
the
periodic
table
equals the
number of
electrons
in the
outermost
shell
we can explain
trends in
reactivity as we
go down a
group in terms
of
The distance between the
outermost electrons and the
nucleus
the number of
occupied inner
shells (energy
levels) in the
atoms
C3
1.3
the elements in
group 1 of the
periodic table are
called the alkali
metals
Their
melting
points and
boiling
points
decrease
going
down the
group
the metals all react with water to
produce hydrogen and the alkaline
metal solution containing the
metal hydroxide
They form 1+ ions in reactions to
make ionic compounds. these are
generally white and dissolve in water,
giving colourless solutions
The reactivity of
alkali metals
increase going
down the group
C3
1.4
Compared with the alkali
metals, transition metals
have much higher melting
points and densities. They
are also stronger and harder
but are much less reactive.
The transition metals do not react
vigorously with oxygen or water.
a transition element can
from ions with different
charges, in compounds that
are often coloured.
Transition elements and their
compounds are important
industrial catalysts.
C3
1.5
The halogens
all form ions
with a single
negative charge
in their ionic
compound with
metals.
The halogens form
covalent compounds
by sharing electrons
with other non-metals
a more reactive halogen can displace a less reactive
halogen from ma solution of one of its salts.
The reactivity of halogens decreases
as you go down the group