Transcript 1.5 Trends in Periodic Table v2 no electronegativity

TRENDS IN THE PERIODIC
TABLE
Important Definitions
 Trend: predictable change in a
particular direction
 Electron Shielding : inner electrons
shield outer electrons from the full
attractive force of the nucleus
 Effective Nuclear Charge (ENC):
charge felt by the valence
electrons after you have
taken into account the
# of shielding electrons
Atomic Radius
 Atomic radius: half of the
distance between the nuclei
of two atoms of the same
element bonded together.
Atomic Radius
 increases as you
move down a group
electrons occupy
consecutively higher
energy levels,
farther from the
nucleus
ENC decreases due
to increased
shielding
H
Li
Na
K
Rb
Atomic Radius
 decreases as you move
across a period
 Electrons are in the same energy
level
 there is more nuclear charge.
 Outermost electrons are pulled
closer.
Na
Mg
Al
Si
P
S
Cl Ar
Atomic Radius Trends
Radius of Cations
 Metals form cations.
 Cations form by losing
electrons.
 Cations are smaller than the
atom they came from – not
only do they lose electrons,
they lose an entire energy
level.
Radius of Anions
 Nonmetals form anions.
 Anions form by gaining
electrons.
 Anions are bigger than the
atom they came from – have
the same energy level, and
nuclear charge (ENC slightly
smaller)
Ionic Radius Trends
 trends follow the same pattern
as atomic radius
 increases as you move down a
group
 due to decreased ENC (increased
shielding)
 decreases as you move across
a period
 due to increasing nuclear charge,
whether the ion is positive or
negative
Ionic Radii Trends
Ionization Energy
 Ionization: removing an
electron from an atom or ion
 1st Ionization energy: energy
required to remove an electron
from an atom
 Must overcome attraction between
electron and nucleus
 2nd Ionization Energy: The
energy required to remove a
second electron from a cation
I.E. for the 1st 10 elements
Symbol First
H
He
Li
Be
B
C
N
O
F
Ne
1312
2731
520
900
800
1086
1402
1314
1681
2080
Second
5247
7297
1757
2430
2352
2857
3391
3375
3963
Third
Why did these values
increase so much?
11810
14840
3569
4619
4577
5301
6045
6276
Ionization Energy
 Group 1: easily loses its 1
valence electron
 Low first ionization energy
 Second ionization energy will be
very high since it now has a stable
octet.
 Group 2: easily lose 2 valence
electrons
 Low first and second ionization
energies
 High third ionization energy
Ionization
Ionization Energy Trends
 decreases as you move
down a group
due to electron shielding
(decreasing ENC)
 increases as you move
across a period
due to the increase in nuclear
charge
Ionization Energy Trends
Electron Affinity
 Electron Affinity: the energy
given off when an electron is
added to an atom to make an
anion.
 elements with high electron
affinities form negative ions in
ionic compounds.
 elements with low electron
affinities form positive ions in
ionic compounds.
Electron Affinity Trends
 same as for ionization
energy
 decreases as you move
down a group due to
increased electron shielding
(decrease in ENC)
 increases as you move
across a period due to
increasing nuclear charge
Electron Affinity Trends