Periodic Trends

Question 1

What is Effective Nuclear Charge (Zeff)?

Answer 1

The pull/attraction valence electrons feel from the nucleus

Question 2

What is the trend for Zeff along a period?

Answer 2

Zeff increases

Question 3

What is the trend for Zeff down a group

Answer 3

No change, stays the same

Question 4

How do you calculate Effective Nuclear Charge

Answer 4

Atomic number - # of core electrons

Question 5

How do you calculate atomic radius?

Answer 5

Nuclei to nuclei divided by 2

Question 6

What are the periodic trends in Atomic Radii

Answer 6

• As n increases, the atomic size increases
• As Zeff increases, the atomic size decreases (feels more pull from nucleus)

Question 7

To obtain a full n-shell and become more stable atoms will?

Answer 7

Gain or lose electrons to become isoelectronic with the closest noble gas

Question 8

What are Cations and how does this affect the atom sized compared to the parent atom?

Answer 8

• Positively charged
• Parent atom loses an electron
• Always smaller than the parent atom

Question 9

What are Anions and how does it affect the size compared to the parent atom?

Answer 9

• Negatively charged
• Parent atom gains an electron
• Always larger than the parent atom

Question 10

What are Isoelectric Ions

Answer 10

• Atoms with the same # of electrons, but a different # of protons
• Less protons, therefore, the electrons feel pull from the nucleus less

Question 11

What is Ionization Energy (IE)?

Answer 11

• The energy required to remove an electron from an atom/ion in the gas phase
• Energy is added to the reaction; endothermic reaction
• Reflects how tightly the electron is held by the nucleus

Question 12

What are the periodic trends for Ionization Energy?

Answer 12

• As n increased ionization energy decreases, as it is further from the nucleus and easier to remove an electron
• As Zeff increases ionization energy increases, as electrons feel more pull toward the nucleus and it is harder to remove and electron.

Question 13

What are the exceptions to the Ionization Energy (IE) periodic trends?

Answer 13

Exceptions (related to special stable arrangements):
1. When there is a filled subshell it is harder to remove an electron
2. Unpaired electrons in degenerate orbitals are more stable then paired electrons

Question 14

What are Successive Ionizations?

Answer 14

• Consecutive ionizations which use more energy when core electrons begin to get removed.
• Successive ionization is possible until no electrons remain.

Question 15

What is Electron Affinity (EA)?

Answer 15

• The desire of an atom to gain an electron in the gas phase
• The amount of energy released when an electron is gained
• Usually, energy is released, and the reaction is negative
• More negative EA value, the higher the EA (easier to add an electron)

Question 16

What are the periodic trends for Electron Affinity?

Answer 16

• As n increases it is harder to add an electron because electrons feel less pull from the nucleus, decreasing EA; a smaller negative number (more positive number)
• As Zeff increases it is easier to add an electron because electrons feel more pull from the nucleus, increasing EA; a more negative number

Question 17

What are the exceptions to the Electron Affinity periodic trends?

Answer 17

• Group 2: Adding an extra electron would force it into a higher energy p-orbital, which is less stable
• Group 15: Adding an extra electron to a half-filled “p” subshell, which is less stable (more repulsion)
• Group 18: Adding an extra electron would occupy a new, higher energy level which is energetically not favourable.