6/16/15 Housekeeping- Exam 3 graded; will return at end of class- Exam 2 re-do’s due tomorrow!- Exam 4 next Tuesday (6/23) instead of Monday? (Would give us

some time to review on Monday)- Alternate proposal: skip lab tomorrow afternoon (Wed., 6/17) and

spend another 30-45 minutes for lecture (3:00 - 3:30-ish)?- Packet 1/3… periodic trends

1

Periodic Trends in Atomic PropertiesPeriodic Trends in Atomic Properties

2

Atomic RadiusAtomic Radius

3

Atomic radii increase down a group.

For each step down a group, electrons enter the next higher energy level.

11.24

Radii of atoms tend to decrease from left to right across a period.

For representative elements within the same period, the energy level remains constant as electrons are added.

This increase in positive nuclear charge pulls all electrons closer to the nucleus.

11.2

Each time an electron is added, a proton is also added to the nucleus. 5

Atomic radii trendsR

adiu

s inc

reas

es

Radius decreases

6

Atomic Radius Trends: Larger Atom in Each Pair

1) N or F

2) C or Ge

3) N or Al

4) Al or Ge

7

Trends in Ionic Radius• Ions in same group have same charge• Ion size increases down the group

– higher valence shell, larger• Cations smaller than neutral atom; Anions bigger than

neutral atom• Cations smaller than anions

– except Rb+1 & Cs+1 bigger or same size as F-1 and O-2

• Larger positive charge = smaller cation – for isoelectronic species– isoelectronic = same electron configuration

• Larger negative charge = larger anion – for isoelectronic series

8

Trends in Ionic Radius

S2- (189 pm) Cl- (181 pm) K+ (133 pm) Ca2+ (99 pm)

18 e- 18e- 18e- 18 e-

16 p 17 p 19 p 20 p

9

Why does the Ca2+ ion have the smallest radius?Hint: consider electron/nucleus interactions

Radii of atoms and

their cations

10

Radii of atoms and

their cations

11

Radii of atoms and

their anions

12

Radii of atoms and

their anions

13

Ionization EnergyIonization Energy

14

The ionization energy of an atom is the energy required to remove an electron from an atom.

Na + ionization energy → Na+ + e-

15

• The first ionization energy is the amount of energy required to remove the first electron from an atom.

He + first ionization energy → He+ + e-

He + 2,372 kJ/mol → He+ + e-

• The second ionization energy is the amount of energy required to remove the second electron from an atom. (Much more difficult!)

He+ + 5,247 kJ/mol → He2+ + e-

He+ + second ionization energy → He2+ + e-

16

Atomic radii trends help explain…R

adiu

s inc

reas

es

Radius decreases

17

Ionization energy trendsIo

niza

tion

ener

gy

decr

ease

s

Ionization energy increases

18

Ionization Energy Trends: Choose the atom in each pair with the highest first ionization energy

1) Al or S

2) As or Sb

3) N or Si

4) O or Cl

19

Solutions to exercises

20

Choose the Larger Atom in Each Pair: N vs F

atomic radius increases

atom

ic ra

dius

incr

ease

s

*N further to the left*

21

Choose the Larger Atom in Each Pair: C vs Ge

atomic radius increases

atom

ic ra

dius

incr

ease

s

*Ge further down*

22

Choose the Larger Atom in Each Pair: N vs Al

atomic radius increases

atom

ic ra

dius

incr

ease

s

*Al further to the left and further down*

23

Choose the Larger Atom in Each Pair: Al vs Ge

atomic radius increases

atom

ic ra

dius

incr

ease

s

*Can’t tell! Opposing trends!*

24

ionization energy increases

ioni

zatio

n en

ergy

de

crea

ses

Choose the atom in each pair with the highest first ionization energy: Al or S

*S lies further to the right*

25

ionization energy increases

ioni

zatio

n en

ergy

de

crea

ses

Choose the atom in each pair with the highest first ionization energy: As or Sb

*As further up*

26

ionization energy increases

ioni

zatio

n en

ergy

de

crea

ses

Choose the atom in each pair with the highest first ionization energy: N or Si

*N is further to the right and higher up*

27

ionization energy increases

ioni

zatio

n en

ergy

de

crea

ses

Choose the atom in each pair with the highest first ionization energy: O or Cl

*Can’t tell! Opposing trends!*

28