CH6 atomic radius trends - Atomic radius, ionization energy, ionic radius and electronegitivity

Periodic trends chemistry

1. Section 3: Periodic Trends

2. Nuclear Charge
•Nuclear charge is the pull that an
electron “feels” from the nucleus.
•The closer an electron is to the nucleus,
the more pull it feels.
•As nuclear charge increases, the
electron cloud is pulled in tighter.
•Increases across a period.

3. Shielding
•As more energy levels are added to
atoms, the inner layers of electrons
shield the outer electrons from the
nucleus.
•Outer electrons are less tightly held.
•Constant across a period.
•Increases down a group.

4. Atomic Radius
•Definition: Half of the distance between
nuclei in covalently bonded diatomic
molecule

5. Electronic
Structure
of Atoms
Atomic Radius
-due to
more
shielding
(more
energy
levels)
i
n
c
r
e
a
s
e
s

d
o
w
n

a

g
r
o
u
p
-due to greater nuclear charge
(more protons)
decreases across a period

6. Atomic Radius

7. Example of Atomic Radius Trend
•Arrange the following elements in order
of increasing atomic radii: Cs, F, K, Cl

8. Electronic
Structure
of Atoms
Cations from metals:
e
–
’s lost
positive (+) charge
smaller
outer shell lost
Anions from nonmetals:
e
–
’s gained
negative (–) charge
larger
less nuclear charge
Ionic Radius

9. Ions
•Here is a simple way to remember
which is the cation and which the anion:
This is a cat-ion.This is Ann Ion.
He’s a “plussy”
cat!
She’s unhappy
and negative.
+ +

10. Cation Formation
11p
+
Na atom
1 valence
electron
Valence
e- lost in
ion
formation
Nuclear charge on
remaining electrons
increases.
Remaining e- are
pulled in closer to
the nucleus.
Ionic size
decreases.
Result: a smaller
sodium cation, Na
+

11. Anion Formation
17p
+
Chlorine
atom with 7
valence e-
One e- is
added to the
outer shell.
Nuclear charge is
reduced and the e- cloud
expands.
A chloride ion is
produced. It is
larger than the
original atom.

12. Ionic Radius
Notice that the anions are larger than the
cations!

13. Example of Ionic Radius Trend
•Arrange the following ions in order of
increasing ionic radii:
Ca
2+
, K
+
, Al
3+
, S
2-
, Cl
-
, Te
2-

14. Electronic
Structure
of Atoms
1. Atoms get ___ down a group due to ___.
A. bigger, greater nuclear charge (protons)
B. smaller, less nuclear charge (protons)
C. bigger, more shielding (levels)
D. smaller, less shielding (levels)
Quick Quiz!

15. Electronic
Structure
of Atoms
2. Atomic radii ___ across a period due to ___.
A. decrease, greater nuclear charge (protons)
B. decrease, less nuclear charge (protons)
C. increase, more shielding (levels)
D. increase, less shielding (levels)
Quick Quiz.

16. Electronic
Structure
of Atoms
3.Which of the following has
the largest radius?
A. Na
B. Mg
C. K
D. Ca
Quick Quiz. WHY?
most
shielding
(levels)
least
nuclear
charge
(protons)

17. Electronic
Structure
of Atoms
4.Metals tend to ________ electrons to
form _________ cations.
A. gain, positive
B. gain, negative
C. lose, negative
D. lose, positive
Quick Quiz.

18. Electronic
Structure
of Atoms
A
t
o
m
i
c

R
a
d
i
u
s

i
n
c
r
e
a
s
e
s
Periodic Trends
Atomic Radius decreases
Can you explain in terms of
nuclear charge & shielding

19. Electronic
Structure
of Atoms
A
t
o
m
i
c

R
a
d
i
u
s

i
n
c
r
e
a
s
e
s
Periodic Trends
Atomic Radius decreases
E
l
e
c
t
r
o
n
e
g
a
t
i
v
i
t
y

?
?
?
Ionization Energy ???
Electronegativity ???
I
o
n
i
z
a
t
i
o
n

E
n
e
r
g
y

?
?
?

20. Electronic
Structure
of Atoms
Ionization Energy (IE):
•energy required to
remove an e
–
Down a Group:
decreases ↓
Across a Period:
increases ↑
WHY?
+

21. Electronic
Structure
of Atoms
d
e
c
r
e
a
s
e
s

d
o
w
n

a

g
r
o
u
p
First IE Trends
-due to
more
shielding
(less
attraction)
increases across a period
-due to greater nuclear charge
(more attraction)
+

22. Electronic
Structure
of Atoms
Example of Ionization Energy Trend
•Arrange the following elements in order of
increasing first ionization energy.
Mg, Na, Si, Al

23. Electronic
Structure
of Atoms
Electronegativity (EN) Trends
•atom’s ability to attract bonded e
–
’s
d
e
c
r
e
a
s
e
s

d
o
w
n

a

g
r
o
u
p
increases across a period
-due to
more
shielding
(less
attraction)
-due to greater nuclear charge
(more attraction)

24. Electronic
Structure
of Atoms
Example of Electronegativity Trend
•Arrange the following elements in order of
increasing electronegativity: B, Na, F, O

25. Electronic
Structure
of Atoms
Overall Reactivity – Very Important!
•The most reactive metals are the
largest since they are the best
electron givers.
•The most reactive nonmetals are
the smallest ones since they are
the best electron takers.

26. Electronic
Structure
of Atoms
Overall Reactivity
0

27. Electronic
Structure
of Atoms
A
t
o
m
i
c

R
a
d
i
u
s

i
n
c
r
e
a
s
e
s
Periodic Trends (Summary)
Atomic Radius decreases E
l
e
c
t
r
o
n
e
g
a
t
i
v
i
t
y

d
e
c
r
e
a
s
e
s
Ionization Energy increases
Electronegativity increases
I
o
n
i
z
a
t
i
o
n

E
n
e
r
g
y

d
e
c
r
e
a
s
e
s
Can you explain all of this
in terms of p’s and e’s?
nuclear charge
shielding

28. Electronic
Structure
of Atoms
1.As you go across period 3 from Na to Ar,
the energy needed to remove an electron
from an atom ______________.
A. decreases due to greater nuclear charge
B. decreases due to less shielding
C. increases due to greater nuclear charge
D. increases due to less shielding
Quick Quiz!

29. Electronic
Structure
of Atoms
2.Alkali metals have lower ionization energies
than noble gases because _____________.
A. alkali metals are smaller with more protons.
B. noble gases are larger with more protons.
C.alkali metals are larger with lower
nuclear charges.
D. noble gases are smaller with fewer protons.
Quick Quiz.
IE: 500 kJ 1500 kJ

30. Electronic
Structure
of Atoms
3.Fluorine is the most electronegative
element because it has ____________.
A. more nuclear charge and more shielding
B. less nuclear charge and more shielding
C. more nuclear charge and less shielding
D. less nuclear charge and less shielding
Quick Quiz.

31. Electronic
Structure
of Atoms
A
t
o
m
i
c

R
a
d
i
u
s

i
n
c
r
e
a
s
e
s
Periodic Trends (Summary)
Atomic Radius decreases E
l
e
c
t
r
o
n
e
g
a
t
i
v
i
t
y

d
e
c
r
e
a
s
e
s
Ionization Energy increases
Electronegativity increases
I
o
n
i
z
a
t
i
o
n

E
n
e
r
g
y

d
e
c
r
e
a
s
e
s
Can you explain all of this
in terms of p’s and e’s?
nuclear charge
shielding