1. Trends in the Periodic Table
Chapter 5

2. Atomic Radii Ionization Energy Electron Affinity Ionic Radii
Trend
Period Trend
Group Trend
Atomic Radii
Ionization Energy
Electron Affinity
Ionic Radii
Electronegativity

3. Atomic Radii
• The exact size of an atom is hard to determine.
• One method for calculating the size of an atom involves calculating the bond radius, which is half the distance from center to center of two like atoms that are bonded together.
• The bond radius can change slightly depending on what atoms are involved.

4. Atomic Radii Atomic Radius Increases as You Move Down a Group
• As you proceed from one element down to the next in a group, another principal energy level is filled.
• The addition of another level of electrons increases the size, or atomic radius, of an atom.
• Because of electron shielding, the effective nuclear charge acting on the outer electrons is almost constant as you move down a group, regardless of the energy level in which the outer electrons are located.

5. Atomic Radii Atomic Radii Decreases as You Move Across a Period
As you move from left to right across a period, each atom has one more proton and one more electron than the atom before it has.
• All additional electrons go into the same principal energy level—no electrons are being added to the inner levels.
• As the nuclear charge increases across a period, the effective nuclear charge acting on the outer electrons also increases.

7. Review 1).What is atomic radii?
2).What is the group trend of the atomic radii on the periodic table?
3).What is the period rend of the atomic radii on the period table?
4).Explain your answers.

8. Ionization Energy
The ionization energy is the energy required to remove an electron from an atom or ion.
Ionization Energy Decreases as You Move Down a Group
• Each element has more occupied energy levels than the one above it has.
• The outermost electrons are farthest from the nucleus in elements near the bottom of a group.
The bigger the atom, the lower the ionization energy.

9. Ionization Energy
Ionization energy tends to increase as you move from left to right across a period.
• From one element to the next in a period, the number of protons and the number of electrons increase by one each.
• The additional proton increases the nuclear charge.
• A higher nuclear charge more strongly attracts the outer electrons in the same energy level, but the electron-shielding effect from inner-level electrons remains the same. (the smaller the atom, the higher the ionization energy)

11. Review 1). What is ionization energy?
2).What is the period trend for ionization energy?
3). What is the group trend for ionization energy?
4). Explain your answers

12. DO NOW
Complete the sentence frames to explain the various trends in the periodic table.
1). Atomic radii decreases as _____, because _________________.
2). Atomic radii increases as ______, because _________________.
3) Ionization energy increases as _________, because __________.
4) Ionization energy decreases as __________, because _________.

13. Electron Affinity
The energy change that occurs when a neutral atom gains an electron is called the atom’s electron affinity .
The electron affinity tends to decrease as you move down a group because of the increasing effect of electron shielding.
• Electron affinity tends to increase as you move across a period because of the increasing nuclear charge.

14. Review 2). What is the period trend for electron affinity?
1). What is electron affinity?
2). What is the period trend for electron affinity?
3). What is the group trend for electron affinity?
4). Explain your answer

15. Ionic Radii
The ionic radius usually increases as you move down a group.
• This trends hold for both positive and negative ions.
• Metals tend to lose one or more electrons and form a positive ion.
• As you move across a period, the ionic radii of metal cations tend to decrease because of the increasing nuclear charge.
• The atoms of nonmetal elements in a period tend to gain electrons and form negative ions.

16. Review 1). What ionic radii?
2).What is the group trend for ionic radii?
3). What is the period trend for ionic radii?
4) Explain your answer

17. Electronegativity
The measure of the ability of an atom in a chemical compound to attract electrons from one another.
Fluorine is the most electronegative element with a value of 4 (arbitrarily assigned)
Electronegativity increases across each period
Electronegativity decreases(or remain the same down a group)
There are a few exceptions with trend in electronegativity.

18. Review 1). What is electronegativity?
2). What is the group trend for electronegativity?
3). What is the period trend for electronegativity?
4). What is the most electronegative element?

19. Valence Electrons
Valence electrons are often located in incompletely filled main energy level.
For main group elements, the valence electrons are the electrons in the outermost s and p subshells.

20. Review 1). What are valence electrons? 2). Where are they found?
3). Why are they so important?