Trends in the Periodic Table

Question 1

What happens when you go along a period?

Answer 1

Atomic radius decreases
Increase in effective nuclear charge
No increase in screening effect

Question 2

What happens when you go down a group?

Answer 2

Atomic radius increases
New energy level
Screening effect

Question 3

Reasons the atomic radius increases down the groups

Answer 3

1. Additional electrons are going into a new energy level (shell) which is further from the nucleus - atomic radius increases
2. Screening effect of inner electrons. Increase in nuclear charge is lessened bc of what is called a screening effect. Even though nuclear charge increases, increase is counteracted by shielding effect of inner energy levels of electrons.

Question 4

Screening effect

Answer 4

In atoms w/ many electrons, electrons in inner energy level or levels help to screen/shield outer electrons from positive charge in nucleus. Attractive force of positive charges in nucleus is lessened by inner energy levels of electrons.

Question 5

Reasons atomic radius decreases across a period

Answer 5

• Increase in effective nuclear charge. Number of protons increases from left to right, greater attractive force on the outer electrons. Draws energy levels closer to nucleus. Atoms become smaller, ie. atom radius decreases
• No increase in screening effect. Extra electron is going into same outer energy level. No increase in screening effect. No additional energy level of electrons to counteract increasing attractive force of the nucleus. ie. atomic radius decreases

Question 6

First ionisation energy of an atom

Answer 6

Minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state

Question 7

Reasons for why first ionisation energy decreases down a group

Answer 7

• Increasing atomic radius. Outermost electrons are becoming further away from attractive force of nucleus. Easier to remove electron from outer energy level.
• Screening effect of inner electrons. Inc. in nuclear charge cancelled out by intervening energy levels. Outermost electrons shielded from attractive force of nucleus + so are easier to remove

Question 8

Reasons for why first ionisation energy increases across a period

Answer 8

• Increasing effective nuclear charge. Left to right across Periodic Table, number of protons increasing. Attraction between nucleus + outer electrons increasing without any increase in screening. Electrons held more firmly, required more energy to remove electron.
• Decreasing atomic radius. Atomic radius decreases from left to right. Electron in outermost level becoming closer to nucleus. More difficult to remove electron due to increased attraction.

Question 9

Exception to the general trend across a period

Answer 9

• First ionisation energies of beryllium + nitrogen are higher than expected
• Irregularities in first ionisation energy trends are explained by fact that any sublevel that is completely filled or exactly half filled has extra stability
• Their first ionisation energy values are higher than expected since it required more energy than expected to break up these stable arrangements by removing an electron

Question 10

Second ionisation energy

Answer 10

The energy required to remove an electron from an ion with one positive charge in the gaseous state

Question 11

why there is a general increase in electronegativity values across periods in periodic table of elements

Answer 11

• bigger nuclear charge

- decreased atomic radius

Question 12

why is there an increase in electroneg value moving from gallium to germanium in periodic table?

Answer 12

• nuclear charge increasing

- atomic radius decreasing

Question 13

why first ionisation energy of smth can be greater than another’s

Answer 13

• greater nuclear charge

- smaller atomic radius

Question 14

why first ion energy of smth can be less than another’s

Answer 14

• greater atomic radius

- most loosely-bound electron more shielded from nucleus

Question 15

how to explain how a graph of ionisation energies provides evidence for energy levels

Answer 15

• (number) groups of ionisations with gradual energy differences between them bc they involve electrons in same energy level/shell
• (number) bigger energy differences between these groups of ionisations bc the (number) energy levels have significantly different energies

Question 16

why there might be a (/large) decrease in first ion energies between two elements

Answer 16

• Has stable outer octet of electrons
• half-full x sublevel has associated stability
• more stable electron configuration
  (eg. Oxygen has 2pₓ² 2pᵧ¹ 2p𝓏¹ while Nitrogen has 2pₓ¹ 2pᵧ¹ 2p𝓏¹

-new energy level (inc atomic radius)

Question 17

unit used to measure first ionisation energy

Answer 17

kilojoules per mole

kJ mol⁻¹

Question 18

using X to represent an element, express the definition of first ionisation energy in the form of a balanced equation

Answer 18

X₍𝓰₎ –> X⁺₍𝓰₎ + e⁻

Question 19

would it take more or less energy to remove the most loosely bound electron from an atom if that electron were not in its ground state?

Answer 19

• less
• already gained energy
• further from nucleus

Question 20

an element has low first ion energy and electroneg. How reactive is it likely to be, and what is likely to happen to it when they react?

Answer 20

• very reactive

- lose electrons/oxidised/ become positively charged

Question 21

the bond energy vaues of the C-Cl bond, the C-Br bond, and the C-I bond are 338, 276, and 238 respectively. Suggest a reason for this trend.

Answer 21

• increased atomic radius
• atoms getting bigger
• decreased electroneg difference

Question 22

which element shows behaviour closes to that of an ideal gas?

Answer 22

Helium

Question 23

why are the atomic radii of chromium, copper and zinc similar?

Answer 23

no change in effective nuclear charge / offset by changed shielding / all d-block