1. ATOMIC RADIUS
Simply: Distance from the nucleus to the valence electrons.
More officially: “half the distance between the nuclei in a molecule consisting of identical atoms”

2. Trends in Atomic Radius
The size of the atoms DECREASES from left to right across a period.
Period Trend
WHY? The nucleus is gaining more protons to become larger and more strongly positive. The stronger nuclear charge attracts the electrons and draws the cloud towards the nucleus.
Period #2

3. Trends in Atomic Radius
The size of the atoms DECREASES from bottom to top of a group.
WHY? There are fewer energy levels at the top of the periodic table. The pull of the nucleus is shielded as more energy levels are added.
Group Trend 1A

4. Application of Atomic Radius
Use your periodic table and knowledge of atomic radius to answer the following multiple choice questions.
Which of the following atoms will have the smallest radius?
a. Tin b. Strontium c. Selenium d. Arsenic
Which of the following atoms will have a larger radius than calcium?
Aluminum b. Copper c. Potassium d. None
In magnesium oxide, MgO, the smaller atom is:
a. Magnesium b. Oxide c. Neither

5. Application of Atomic Radius
Check your answers. Do you have questions?
Which of the following atoms will have the smallest radius?
a. Tin b. Strontium c. Selenium d. Arsenic
Which of the following atoms will have a larger radius than calcium?
Aluminum b. Copper c. Potassium d. None
In magnesium oxide, MgO, the smaller atom is:
a. Magnesium b. Oxide c. Neither

6. Ionic Radius of Cation
Cations form by losing electrons to become stable. As electrons are lost, the atom becomes smaller. Therefore, cations are smaller than their corresponding neutral atoms.

7. Ionic Radius of Cation Draw the orbital diagram for neutral potassium.
Draw the orbital diagram for the potassium cation.
Compare your drawings. Does the trend make sense?

8. Ionic Radius of Anion
Anions form by gaining electrons to become stable. As electrons are added, the atom becomes larger. Therefore, anions are bigger than their corresponding neutral atoms.

9. Ionic Radius of Anion Draw the orbital diagram for sulfur.
Draw the orbital diagram for the sulfide ion.
Does the trend make sense?

10. Energy required to remove an electron from an atom.
Ionization Energy
Energy required to remove an electron from an atom.

11. Trend in 1st Ionization Energy
Based on what you know about the octet rule, which atoms might WANT to have electrons removed? Which ones might NOT WANT to have electrons removed?
The IE INCREASES from left to right across a period.
Period Trend
WHY? The nucleus is gaining more protons to become larger and more strongly positive. The nucleus holds tightly to the electrons. Therefore, HIGH ENERGY is needed to remove an electron.

12. Trend in 1st Ionization Energy
The ionization energy of elements INCREASES from bottom to top of a group.
WHY? There are fewer energy levels at the top of the periodic table. The pull of the positive nucleus is NOT shielded by few energy levels. At the bottom of the table, the pull of the nucleus IS SHIELDED by the many energy levels. Therefore, LOW ENERGY is needed to remove an electron from a large atom.
Group Trend

13. Application of 1st Ionization Energy
Use your periodic table and knowledge of ionization energy to answer the following multiple choice questions.
Which of the following atoms will have the smallest IE?
a. Tin b. Strontium c. Selenium d. Arsenic
Which of the following atoms will have a larger IE than calcium?
Aluminum b. Copper c. Potassium d. None
In magnesium oxide, the atom with the smallest ionization energy is:
a. Magnesium b. Oxide c. Neither

14. Application of 1st Ionization Energy
Check your answers. Do you have questions?
Which of the following atoms will have the smallest IE?
a. Tin b. Strontium c. Selenium d. Arsenic
Which of the following atoms will have a larger IE than calcium?
Aluminum b. Copper c. Potassium d. None
In magnesium oxide, the atom with the smallest ionization energy is:
a. Magnesium b. Oxide c. Neither

15. 2nd & 3rd Ionization Energy
You have learned about ionization energy already, but there is more to the story...
1st Ionization Energy - energy required to remove the first electron from an atom
2nd Ionization Energy - energy required to remove the second electron from an atom
3rd Ionization Energy - energy required to remove the third electron from an atom

16. 2nd & 3rd Ionization Energy
The pattern on the periodic table requires more thought for predicting 2nd and 3rd IEs
Example: Aluminum
Draw the orbital diagram for Al.
1st IE = 580 kJ/mol (removes the highest energy electron – the lone 3p)
2nd IE = 1815 kJ/mol (removes the next highest energy electron – a 3s)
3rd IE = 2740 kJ/mol (removes the 3rd highest energy electron – the final 3s)
4th IE = 11,600 kJ/mol (removes a “core electron” or a non-valence shell electron – WILL NOT OCCUR)

17. 2nd Ionization Energy
2nd Ionization Energy - energy required to remove the second electron from an atom
Compare the 2nd ionization energy of Mg with the 2nd ionization energy Na.
Thought process:
Magnesium needs to lose two electrons to become stable, and sodium needs to lose one electron to become stable.
Who will require more energy to take the second electron?
Answer: Sodium is STABLE after losing one electron, and it will require LOTS of energy to remove a second.

18. Electronegativity
The ability of an atom to draw electrons from another atom closer to itself when in a chemical bond.

19. Trend in Electronegativity
The EN INCREASES from left to right across a period.
Period Trend
WHY? The nucleus is gaining more protons to become larger and more strongly positive. The nucleus holds tightly to the electrons. Therefore, the strong nucleus is able to draw the bonding electrons closer.

20. Trend in Electronegativity
The electronegativity of elements INCREASES from bottom to top of a group.
WHY? There are fewer energy levels at the top of the periodic table. The pull of the positive nucleus is NOT shielded by few energy levels. At the bottom of the table, the pull of the nucleus IS SHIELDED by the many energy levels. Therefore, the shielded nucleus is unable to draw the bonding electrons closer.
Group Trend
Notice: Noble gases have NO electronegativity since they do not form bonds.

21. Applications of EN
Answer the following questions using your periodic table and understanding of EN.
Which of the following has the greatest electronegativity?
Nitrogen b. Bismuth c. Silicon d. Neon
In water, H2O, which atom is holding the bonding electrons closest to itself?
a. Hydrogen b. Oxygen c. Neither

22. Applications of EN
Check your answers. Do you have questions before we move on to ionic radius?
Which of the following has the greatest electronegativity?
Nitrogen b. Bismuth c. Silicon d. Neon
In water, H2O, which atom is holding the bonding electrons closest to itself?
a. Hydrogen b. Oxygen c. Neither

23. Applications of Periodic Trends
Let’s look at 5-3 Review & Reinforcement.
Which ATOM has the larger atomic radius?
Which ION has the smaller atomic radius?
Which atom or ion has the larger ionization energy?
Question 33 - Why is there such a large jump in ionization energy between the second and third ionization energies for magnesium?

24. More Applications of Trends
Let’s look at 5-3 Practice Problems.
1-5 Answers
Question 6: Which is largest: a K atom, a K+1 ion, or an Rb atom?
Question 7: Which of the following is the largest: a Cl atom, a Cl- ion, or a Br atom?
Question 8: Which of the following is the smallest: a Li atom, a Li1+ ion, or a Na atom?
Question 9: Which of the following is the largest: a Te2- ion, an I- ion, or an Xe atom?

25. Sample Discussion Question
Which is the smaller atom: oxygen or nitrogen? Why?
Which atom has higher ionization energy: fluorine or chlorine? Why?