Chapter 14

Chemical Periodicity

The Periodic Table Revisited

What did they do:

1. J.W. Doberiener

2. J.A.R. Newlands

3. Dmitri Mendeleev

4. Henry Mosely

Periodic Law:

The chemical and physical properties of the elements are periodic functions of their atomic number.

(Not all elements follow this)

Review Parts of Periodic Table

Trends

1. Atomic radius

a. Monatomic atoms – distance from the nucleus to the

outermost electron of an atom

b. Diatomic – ½ the distance from one adjacent atom to another

c. Rules: Group or family

Atomic number is directly proportional to the atomic

radius

d. Ex. Which has a larger atomic radius?

Li Cs

2s1 6s1

e. Rules for: Series or period

atomic number is a indirect proportion to the atomic

radius

f. Ex. Which has a larger atomic radius? Li or Ne

Li Ne

2s1 2p6

What could you look at if they are in the same row?

# protons

3 p+ 10p+

More protons has a stronger nuclear attraction

(pulls in close)

g. Special cases

1. Out of the following pairs state which has a larger atomic radius.

S or Po

Mg or Cl

Li or Rn

Summary

1. Start with the last electron configuration

2. Look for same configuration, more energy means it is larger

3. Look for same last energy level, more protons makes it smaller

4. Look for adjoining element

2. Ionization Energy (IE)

a. Energy needed to remove the outermost electron from an

atom in its gaseous state

b. Unit: kJ/mole

c. Rules: Group or family

1. Atomic number is indirectly proportional to the IE

2. Increasing atomic number leads to a lower IE

3. Ex. Which would have a higher IE?

Li Cs

Li Cs

2s1 6s1

(high IE) (low IE) electrons further away, so it’s easier

to remove

d. Rules: Series or Periods

1. Atomic number is directly proportional to the IE

2. Increasing atomic number equals higher IE

3. Ex. Which would be higher Li or Ne?

Li Ne

2s1 2p6

(same energy level)

3 protons 10 protons

(stronger nuclear attraction)

higher

4. Which is higher?

Mg or P

Na or Cl

5. Ex. Rank in terms of IE from high to low

Sr, C, F

6. Special cases:

Which has higher IE, N or O?

**** ONLY TAKE BALANCE INTO CONSIDERATION WHEN DEALING WITH ADJACENT ELEMENTS.

Summary

Look at:

1. Energy levels

2. How many protons

3. Balance of adjacent elements

Rank from low to high IE

Ca Sr As Se

3. Second ionization energy, IE2

a. The energy needed to remove the second outermost electron AFTER the outermost has already been removed.

b. What IE1 looks like:

Na + IE1 Na+ + e-

11 p+ 11 p+

11 e- 10 e_

c. What will IE2 look like:

Na+ + IE2 Na+2 + e-

11 p+

10 e-11 p+

9 e-

4. Third ionization energy a. Energy needed to remove the

third outermost electron after the two outermost electrons have been removed.

b. What it looks like:

Na+2 + IE3

11p 11p

9e 8e

c. IE3 is always applied to a (+2) ion.

d. IE2 is always applied to a (+1) ion.

e. How would you rank IE, IE2, IE3?

(high to low)

IE3 > IE2 > IE

f. Examples:

1. Which of the following elements would have the

higher IE2?

Be, C or F

Be+ C+ F+

2s1 2p1 2p4

4p+ 6p+ 9p+

lowest highest

2. Which of these would have the highest IE3 ?

Be, C, F

Be+2 C+2 F+2

1s2 2s2 2p3

6 p+ 9p+

Highest lowest

(closest to nucleus)

3. Rank the following elements in terms of IE2 from high to low

O+ S+ F+

g. Summary of IE

1. Look at energy levels (how close to the nucleus)

2. Consider how many protons

3. Consider adjacent elements (use balance vs

unbalance)

4. Ex. Rank in terms of IE from high to low: Ca, Sr, As, Se

5. Chemical activitya. An elements ability to replace

another element in a chemical compound

b. Which is more reactive?

Li, Na, K

c. Rules

1. Metals

a. Group or family – activity increases with increasing

atomic number

b. Series or Period – activity decreases with increasing atomic number

c. Ex. Rank activity from low to high

Be, Ca, Ba

low high

2. Nonmetals a. Group or family- activity

decreases down the group

b. Series or period- activity increases as atomic

number increases

c. Rank from low to high

Se, S,Cl

d. What is the most active metal?

e. What is the most active nonmetal?

6. Ionic radius

a. the distance from the nucleus to the outermost electron of a naturally occurring ion

b. Want to achieve the electron configuration of a noble gas

c. Examples:

1. Which would have a larger ionic radius? Sr, Mg, Al

2. Rank in terms of larger ionic radius large to small:

N, S, F, Br

d. Cations are SMALLER than the atom from which they naturally come.

e. Anions are LARGER than the atom from which they naturally come.

f. Cations are positive.

g. Anion are negative charge.

7.Electron Affinity a. The energy absorbed or released when an atom gains an electron

b. X + electron + EA X−

c. Higher energy less stable or balance

d. Lower energy more stable or balance

e. Ex. Which will have the highest EA

B N F

Before 2p1 __ __ __ 2p3 __ __ __ 2p5 __ __ __

After 2p2 __ __ __ 2p4 __ __ __ 2p6 __ __ __

Noble gas configuration will be the lowest

f. Equations using EA or IE

1. Show Mg losing an electron

Mg + 738 kJ Mg+ +e−

State whether it is endothermic or exothermic

2. Show Mg gaining an electron

Mg + e− Mg− + 19 kJ

Is this endothermic or exothermic?