Unit 5: periodicity (2)

Question 1

Elements in the same family (column) have what in common?

Answer 1

They have similar chemical and physical propreties, because they have the same number of valence electrons in the same kind of orbitals (ex: s, p, d…)

Question 2

Which variations in propreties can be predicted using the periodic table?

Answer 2

1) Ionization energy
2) Atomic radius
3) Ionic radius
4) Electronegativity
5) Electron affinity

Question 3

What is the Effective nuclear charge?

Answer 3

• Zeff
• Definition: The nuclear charge felt by an electron if there were no intervening electrons equals the atomic number, Z.
• Because there are intervening electrons, the nuclear charge that an electron experiences is reduced to a value called the EFFECTIVE NUCLEAR CHARGE, or Zeff

Question 4

What is the Shielding effect?

Answer 4

Inner electrons block outer electrons from the attractive pull of the nucleus and repel them. As result, outer electrons will experience a lower attraction to nucleus, so lower Zeff.

Question 5

What is penetration?

Answer 5

Within the same shell, s orbital is closer to the nucleus and experiences a larger Zeff, resulting in a lower energy of the s orbital.

Question 6

How to calculate Zeff?

Answer 6

Zactual - Electron shielding
or
atomic # - inner electrons

*Where inner electrons are all the electrons except the valence one

Question 7

The biggest distance with the nucleus, the smaller the Zeff, true or false?

Answer 7

True!

Question 8

Which electron, in a 2s vs 3s orbital, has a lower value of Zeff? *****

Answer 8

3s has lower Zeff, because it as more shielding than the 2 s.

Question 9

Periodic table trend concerning Zeff?

Answer 9

• Increase orbital size (number of shells) decreases the nuclear charge an electron experiences
• Increasing the number of protons increases the nuclear charge an electron experiences (ex: Na = 1 and Mg = 2)

Question 10

Periodic table trend for the atomic radius?

Answer 10

• Atomic radius increases has the number of shells increases
• Atomic radius decreases as the atomic number increase, because of the increase in Zeff (Valence electrons are held more tightly!)

Question 11

Which is the most reactice metal and why?

Answer 11

• Francium (Fr) is most reactive, because it only has 1 eletron, and since electron is the farther from nucleus, it will be the easiest to give!

Question 12

Periodic table trend for ionic radius?

Answer 12

• Down a group: size of ions increases
• Across a period: Size is complicated with transition from metal to non-metal (there are exceptions!)

Question 13

How do cations behave concerning their ionic radius?

Answer 13

When electron is removed from an atom, the radius of cation is always smaller because:
- Lose the valence shell
- Principal quantum number is smaller
- Zeff increases (more attraction) for the remaining electrons!

Question 14

How do anions behave concerning their ionic radius?

Answer 14

• When adding electrons to an atom, resulting anion is larger than it’s atom
• Zeff decreases, because proton to electron ratio decreases
• Gaining electrons in valence shell results in more repulsions between electrons

Question 15

What are isoelectronic series?

Answer 15

A serie or ions/atoms that have the same number of electrons!

• Ex: O2-, F-, Ne, Al3+ all have 10 electrons
• They however have different #protons
• Size of isoelectronic ions decreases as atomic number Z increases because the positive charge of nucleus increases

Question 16

What is iozination energy?

Answer 16

Amount of energy needed to remove an electron form a gaseous atom or ion!
*When energy is added, electrons jump to a higher energy level

Question 17

Periodic table trend for ionization energy?

Answer 17

• Lowest ionization energy is for the alkali metals
• Highest ionization energy is for the noble gases
• However, there are exceptions so no 100% clear pattern

Question 18

First ionization energy?

Answer 18

• Increases left to right along a period because of increasing Zeff. Electrons are more tightly held to nucleus (makes sense because non-metals don’t want to give their electrons!)
• Decreases going down a group, because electrons are farther from nucleus, so easier to remove.

Question 19

Irregularities 1 (for 2A elements)?

Answer 19

• Group 2A elements (Be and Mg) have slightly higer Ei values than expected.
• Boron (B) has lower Ei than Be because it’s 2p electron is shielded by 2s electrons.
• Always easier to loose an electron when it’s not paired!

Question 20

Irregularities 2 (for 6A elements)?

Answer 20

• Group 6A (O, S) have slightly lower Ei values than expected

Question 21

Electronegativity?

Answer 21

The ability of an atom to attract electrons

Question 22

Periodic trend on electronegativity?

Answer 22

• From left to right: increased electronegativity
• From top to bottom: decreased electronegativity (because the more shells you have, the easiest it is to lose an electron, so you want to gain electrons less!)

Question 24

Electron affinity?

Answer 24

Change in energy when an electron is added to an atom in the gas phase
*The more negative the electron affinity is, the more favorable it is to add an electron to an atom! (+ is it very electronegative)

Question 25

Periodic trend for electron affinity?

Answer 25

• Left to right: it tends to increase along a period, because of the increasing effective nuclear charge
• Down a group: tends to decrease because of the increasing orbital size, so less attraction of an outer electron (and less electronegativity)
  *There are some exceptions to the rule!