Chapter 2: 2.2 Periodic Trends

Question 1

Define:
Effective nuclear charge

Answer 1

The attractive force felt by a valence electron to the nucleus

or

The net positive charge experienced by the valence electrons when they are shielded (screened) by the core electrons from the full charge of the nucleus

Question 2

State the trend of the effective nuclear charge as we move across a row of the periodic table from left to right

Answer 2

The effective nuclear charge increases

Question 3

How does one calculate effective nuclear charge?

Answer 3

Nuclear charge - Core electrons

Question 4

What is nuclear charge?

Answer 4

Nuclear charge is equal to atomic number

Question 5

Define:
Atomic radius

Answer 5

Half the length of a bond formed by two atoms of the same element

Question 6

Define:
Internuclear distance

Answer 6

Distance between 2 nuclei

Question 7

What are atomic and ionic radii usually expressed in?

Answer 7

Picometers
Angstrom units (100 picometers)

Question 8

State the relationship between the atomic size and the effective nuclear charge

Answer 8

Inverse relationship

As atomic size decreases, effective nuclear charge increases due to increased valence electron attraction

Question 9

State the change in size of atoms as one moves down a group

Answer 9

Atomic size increases as more electrons are present, requiring more orbitals with higher n values.

The size of orbitals increase with n and thus with it, the overall size of the atom

Question 10

What are the exceptions to the general rules of atomic size?

Answer 10

d and f orbitals have poor shielding properties, allowing p electrons to be strongly attracted to the nucleus, making the atomic radius smaller

Question 11

Why are double and triple bonds typically shorter than single bond lengths?

Answer 11

They contain more electrons that pull the nuclei together

Question 12

State the trend of bond lengths as one goes across from left to right on the periodic table

Answer 12

Bonds lengths decreases

Question 13

True or False:
Anions are smaller than neutral atoms

Answer 13

False, anions are larger than neutral atoms and cations are smaller than neutral atoms

Question 14

Dications are _______ than monocations of the same element

Answer 14

Smaller

Question 15

Dianions are ______ than monoanions of the same element

Answer 15

Larger

Question 16

Define:
Ionization energy (IE)

Answer 16

The Minimum amount of energy required to remove a valence electron from a gas-phase atom

Question 17

Since energy must be ________ to remove an electron, IEs are always ________ quantities

Answer 17

Absorbed
Positive

Question 18

State the trend for energy required in successive ionization

Answer 18

The energy required for each successive ionization increases because the net positive charge of the nucleus felt by the remaining electrons is increasing. As a result, the remaining electrons are held more tightly to the nucleus

Question 19

State the correlation between IE and Effective nuclear charge

Answer 19

IE increases from left to right across each row as the effective nuclear charge increases(directly proportional)

Question 20

Why does the IE decrease when going down a group?

Answer 20

Atoms get larger as we move down a group, the larger distance between the nucleus and the valence electrons means its easier to rip electrons off

Question 21

Define:
Electron affinity

Answer 21

The change in energy (or enthalpy) in gas phase process

or

The change in energy to gain electron

Question 22

What are the possibilities for electron affinity?

Answer 22

Thermodynamically favoured (H<0)
Thermodynamically not favoured (H>0)

Question 23

What are some anomalies for electron affinity?

Answer 23

Group 2
Group 15
Noble gases

Question 24

Does electron affinity decrease when going down a group?

Answer 24

Yes

Question 25

Define:
Electronegativity

Answer 25

“The ability of an atom to draw a pair of electrons of a bond to itself”

or

The ability of an atom participating in a chemical bond to draw electron density to itself

Question 26

State electronegativity trends on the periodic table

Answer 26

Electronegativity tends to decrease going down the groups (due to increasing atomic size)
Electronegativity tends to increase going across the rows

Question 27

Where are the most electromagnetic elements located on the periodic table?

Answer 27

Top right corner