TRENDS IN PERIODIC TABLE
PROPERTY
ACROSS A PERIOD
DOWN A GROUP
NOTABLE
EXCEPTIONS
Atomic Radius
→ Decreases
↓ Increases
Zeff increases

If Zeff increases,
then there is a
strong attraction
between
the 
outermost
electrons and the
nucleus
which
results
in
a
smaller atomic
radii.
Principal
quantum
number (n)
increases
As
n
increases, the
orbitals get
larger which
results in a
larger atomic
radii.
Ga same size
with Zn
Sb slightly
bigger than Sn


Electronegativity
→ Increases

Towards the left 
of the table,
valence shells are
less than half full,
so these atoms
(metals) tend to
lose
electrons
and have low
electronegativity.
Towards
the
right of the table,
valence shells are
more than half
full, so these
atoms
(nonmetals) tend
to gain electrons
and have high
electronegativity.
↓ Decreases
Down
a
group,
the
number
of
energy levels
increases,
and so does
the distance
between the
nucleus and
the
outermost
orbital. The
increased
distance and
the increased
shielding
weaken the
nuclear
attraction,
and so an
atom
can’t
attract
electrons as
strongly.
EXPLANATION

Because the
electrons
added in the
transition
elements are
added in the
inner
electron shell
and at the
same time,
the
outer
shell remains
constant, the
nucleus
attracts the
electrons
inward.
Electron Affinity
→ Increases

↓ Decreases
Because
of 
increased
nuclear charge.
The electron
is
being
added
increasingly
further away
from
the
nucleus
which
becomes less
tightly bound
and can be
easily
removed.
1A to 2A
4A to 5A


Ionization Energy
→ Increases


Ionic Radius

↓ Decreases
Zeff increases

The larger the
effective nuclear
charge, the more
energy it takes to 
remove it
Valence
electrons are
farther from
nucleus
They
are
easier
to
remove
→ Decreases
↓ Increases
Ionic
radius 
decreases
moving from left
to right across a
row or period.
More protons are
added, but the
outer
valence
shell remains the
same, so the
positively
charged nucleus
Principal
quantum
number (n)
increases
2A > 3A
5A > 6A

1A to 2A: The
electron that
was
just
added has to
go to a p
orbital
instead of an
S orbital. This
causes
the
electron to be
farther away
from
the
nucleus and
feels
more
repulsion.
4A to 5A: The
electron that
is added goes
to the orbital
that
is
already
occupied
which then
creates
repulsions.
It takes a
greater
amount
of
energy
to
remove
an
electron from
orbitals that
are half-filled
or
completely
filled.
draws in the
electrons more
tightly. But for
the nonmetallic
elements,
the
ionic
radius
increases
because there are
more electrons
than protons.
→ Decreases
Metallic
Character


Zeff increases

Increased
Zeff
means
the
electrons
are
more difficult to
remove.
↓ Increases
The size of an
atom
increases
which leads
to
lesser
attraction
between the
nuclei
and
the electrons,
thus
the
outermost
electrons of a
metallic atom
is
loosely
bound.