Trends in the Periodic Table

Question 1

What are the four important trends in the periodic table?

Answer 1

1. atomc radius
2. ionization energy
3. electron affinity
4. electronegativity

Question 2

What is the atomic radius?

Answer 2

the estimate of the size of an atom from its nucleus to its outer perimeter

Question 3

How can atomic radius be measured and why do they need to be measured this way?

Answer 3

• a radius of an atom can be determined based on the distance between 2 atoms in compounds
• they need to be measured this way because they don’t have a well-defined boundary - it is fuzzy so the actually atom size cannot be measured individually

Question 4

what unit are atomic radii measured in?

Answer 4

picometers (pm) 1pm = 10^-12 m

Question 5

What is the general trend of atomic radii?

Answer 5

it gets smaller as you move up and to the right on the periodic table
- as you move to the right on a period the atomic radius decreases
- as you move group a group the radius of an atom increases

Question 6

Describe the sheilding effect

Answer 6

in an atom with multiple electrons, the valence electrons are attracted by the protons in the nucleus but also repelled by the inner electrons in the atom

Question 7

What does the shielding effect lead to

Answer 7

• the decrease in attraction between an electron and the nucleus

Question 8

The more electron shells, the greater the sheilding effect experienced

Question 9

what is effective nuclear charge

Answer 9

the force of attraction by posistive nucleus on electrons (electron cloud)

Question 10

What impacts the net force that an electron experiences in an atom?

Answer 10

• due to the attractive forces of the positively charged nucleus
• reduced by the sheilding or screening from other electrons between the outermost electron and the nucleus itself

Question 11

How do you calculate effective nuclear charge?

Answer 11

Zeff = Z-S
effective nuclear charge = atomic number - the number of sheilding electrons (or the sheilding constant)

DON’T NEED TO KNOW THO

Question 12

Explain why the atomic radius decreases within a period?

Answer 12

• the number of protons and electrons increases
• however, electrons are added to the same energy level
• so the number of inner core electrons remains constant so there is no additional shielding effect
• effective nuclear charge increases
• the valence elecrons are strongly attracted to the nucleus so you get a decrease in the size of the atom

Question 13

Explain why the atomic radius increases as you move down a group.

Answer 13

• there are more energy levels as you move down the group so the electrons become farther away from the nucleus
• electrons in the inner energy levels block or shield the valence electrons from the attraction of the nucleus
• the effective nuclear charge decreases
• the electrons are not held as tightly
• atomic radius increases

Question 14

what is ionic radius?

Answer 14

the measure of the size of an atom -> the distance from the centre of an ion to the outermost electrons

Question 15

What unit is ionic radius measured in?

Answer 15

picometers

Question 16

What happens when you form metal ions?

Answer 16

• the metal loses electrons
• each remaining electron experiences more attraction to the nucleus
• the effective nuclear charge increases
• the metal ion is smaller than the uncharged atom

Question 17

what happens when you form non metal ions?

Answer 17

• each electron experiences less attraction to the nucleus
• there is greater electron-electron repulsion
• the non-metal ion is larger than the uncharged atom

Question 18

What is ionization energy?

Answer 18

the amount of energy required to remove an electron from a gaseous atom

Question 19

It takes energy to overcome the attractive force of the nucleus and pull an electron away from a neutral atom

Question 20

what is the first ionization energy

Answer 20

the energy required to remove the least attracted electron from a gaseous atom of that element. This least attracted electron is in the outer shell of the atom

Question 21

What is second ionization energy?

Answer 21

the amount of energy required to remove a second electron from a gaseous atom

Question 22

What happens to ionization energy from left to right within a period

Answer 22

it increases

Question 23

What happens to ionization energy as you move down a group?

Answer 23

it decreases

Question 24

What are the three factors that affect ionization energy?

Answer 24

• nuclear charge - the strength of the pull of the nucleus on electrons
• atomic radius
• shielding effect - electrons in the inner levels shield electrons in the outer energy level from the pull of the nucleus

Question 25

Why does the ionization energy increase from left to right along a period?

Answer 25

As the atomic radius decreases, the valence electrons are experiencing a stronger attractive force from the nucleus -> the effective nuclear charge increases, so it requires more energy to pull the electron away and ends up with a larger ionization energy

Question 26

Explain why ionization energy decreases from top to bottom of a group

Answer 26

• As atomic radius increases, the valence electrons experience a weaker attractive force from the nucleus (effective nuclear charge decreases)
• so, less energy is required to pull them away
• so, a lower ionization energy

Question 27

What is a trend in ionization energy? Explain it.

Answer 27

Ionization energy gets larger as you remove more electrons from an atom. As an electron is removed, the atom becomes an ion which is postively charged. So there are more protons than electrons. This leads to greater nuclear charge experienced by outer electrons making it harder (i.e.more energy required) to remove them from the ion

Question 28

what is electron affinity?

Answer 28

the energy change that occurs when an electron is added to a neutral, gaseous atom to form an anoin

Question 29

Describe more things about electron affinity.

Answer 29

most often, energy is released when an electron is added. However, sometimes enery is required to add the electron.

The greater the negative value the more stable the anion

Question 30

What does electron affinity do along a period?

Answer 30

it increases from left to right

Question 31

What is the electron affinity trend as you move down a group?

Answer 31

it decreases

Question 32

What does a larger electron affinity mean?

Answer 32

it is easier to add electrons to that atom.

Question 33

If the number of electron affinity is positive, energy is released. A positive number indicates energy is required to add the electron.

Question 34

Explain the trend in electron affinity accross a period.

Answer 34

As the valence electrons experience stronger attractive forces from the nucleus, more energy is released when a new electron is added.

Question 35

Explain. why the electron affinity decreases down a group

Answer 35

electrons added to shell further away from the nucleus and experience more shilding effect, so less energy is released when a new electron is added.

Question 36

A very negative value of electron affinity indicates that a lot of energy is released when an electron is added to a gaseous atom and that such a procuess is very likely to occur.

Question 37

What is electronegattivity?

Answer 37

the ability of an atom to attract the shared electrons towards itself in a bond

Question 38

What does a high electronegativity mean?

Answer 38

a stronger attraction for electrons

Question 39

Electronegavitity extras

Answer 39

• cannot be measured experimentally
• calculted instead using physical properties such as ionization energy
• each element is therefore assigned an electronegativity value

Question 40

What is the electronegativity trend from left to right?

Answer 40

it increases

Question 41

Explain the elctronegativity. on the period.

Answer 41

the number of protons increases and shielding effect is constant, so shared electrons are attrated more strongly.

Question 42

What is the electronegativity trend down a group?

Answer 42

it decreases

Question 43

Explain the elecctronegativity trend down a group.

Answer 43

the number of protons increases but also more inner electrons, increasing shielding effect. So shared electrons are less attracted to the nucleus.