Transcript 7c.trends-periodic- - Gleneaglesunit1and2chemistry2012

The Periodic Law says:
PERIODIC
LAW states that when
elements are arranged in order of
increasing atomic number, there is a
periodic repetition of their physical
and chemical properties.
Trends in the periodic table:
Atomic Radius
Ionization Energy
Electron Affinity
Electronegativity
Metallic character
Atomic Radius
}
Radius
this
is half the distance between the centres of
two atoms of that element.
ALL Periodic Table Trends
Influenced
by three factors:
1. Energy Level
• Higher energy levels are further
away from the nucleus.
2. Charge on nucleus (# protons)
• More charge pulls electrons in
closer. (+ and – attract each other)
3. Shielding effect (blocking effect?)
#1. Periodic trends in atomic
radius
H
 Going down a
group the atomic
radius increases
because…
 each atom has
another energy
level, so the
atoms get
bigger.
Li
Na
K
Rb
#1. Atomic Size - Period Trends
 Going
from left to right across a period, the
size gets smaller.
 Elements
have same energy levels but,
there is more nuclear charge so
 outermost electrons are pulled closer.
Na
Mg
Al
Si
P
S Cl Ar
Ions
• An ion is an atom (or group of
atoms) that has a positive or
negative charge due to the
transfer of electron/s between
atoms.
Ions
Metals tend to LOSE electron/s,
from their outer energy level to form
positively charged ion = “cation”
Cations are smaller than the atom
they come from because not only
do they lose electrons, they lose
an entire energy level.
Ions
Nonmetals
tend to GAIN one or
more electrons and become negative
ion called “anions”
are bigger than the atom
they come from because they have
the same energy level, but a greater
area the nuclear charge needs to
cover
Anions
Shielding
 The
shielding effect
is the decrease in
attraction between
an electron and the
nucleus in any atom.
Core charge
 Core
charge is
the effective
nuclear charge
experienced by
an outer shell
electron.

Can be found by
subtracting the number
of inner-shell electrons
from the nuclear
charge.
#2. Trends in Ionization Energy
Ionization
energy is the energy
required to remove outer
electron from an atom in its
gaseous state
The energy required to remove
the first electron from the outer
shell is called the first ionization
energy.
Ionization Energy
The
second ionization energy is
the energy required to remove
the second electron.
• Always greater than first IE.
The third IE is the energy
required to remove a third
electron.
• Greater than 1st or 2nd IE.
Ionization Energy - Group trends
As
you go down a group,
the ionisation energy
decreases because...
• The electron is further away from the
attraction of the nucleus, and and
thus easier to remove the outermost
one.
• There is more shielding.
Ionization Energy - Period trends
 Going
across a period, ionisation
energy generally increases from left
to right because…..
 the atomic radius decreases, that is, the
atom is smaller. The outer electrons are
closer to the nucleus and more strongly
attracted to the centre. Therefore, it becomes
more difficult to remove the outermost
electron.
#3. Periodic trends in Electronegativity
 Electronegativity
is the tendency
for an atom to attract electrons to
itself when it is chemically
combined with another element.
Electronegativity Group Trend
As you go down a group
the electronegativity
decreases because…
The
further down a group, the
farther the electron is away
from the nucleus, thus, more
willing to share.
Electronegativity Period Trend
As
you move across a period,
electronegativity generally
increases from left to right
because…..
 At the right end are the
nonmetals. They want more
electrons.
 Electronegativity
is related to
ionization energy. Electrons with low
ionization energies have low
electronegativities because their
nuclei do not exert a strong attractive
force on electrons. Elements with
high ionization energies have high
electronegativities due to the strong
pull exerted on electrons by the
nucleus.
Periodic trends in
electron affinity
• electron affinity describes the ability of an
atom to accept an electron.
• Electron affinity increases from left to right
within a period. This is caused by the
decrease in atomic radius.
• Electron affinity decreases from top to
bottom within a group. This is caused by the
increase in atomic radius.
Summary of Periodic Table
Trends