Module 1.3 Periodicity

Which property has the same value for all elements in group 2 of the periodic table?

• Valency

• First ionisation energy

• Electronegativity

• Atom size

Answer explanation

The property that has the same value for all elements in Group 2 of the periodic table is Valency. All Group 2 elements, also known as the alkaline earth metals, have a valency of 2 because they all have two electrons in their outermost shell.

The other properties vary across the group:

• First ionisation energy decreases as you move down the group due to increasing atomic size and shielding.

• Electronegativity also decreases down the group as the atoms become larger.

• Atom size increases as you move down the group due to the addition of extra electron shells.

Consider the elements in the second period of the periodic table.

What is the general trend in the first ionisation energy of these elements?

• Decreases from lithium to neon

• Decreases from lithium to carbon then increases to neon

• Increases from lithium to carbon then decreases to neon

• Increases from lithium to neon

Element X lies in the middle of a group of nine elements on a periodic table.

Which element is most likely to have a lower electronegativity than X?

• α

• β

• γ

• δ

Answer explanation

Element γ is most likely to have a lower electronegativity than element X. In the periodic table, electronegativity generally decreases as you move down a group and increases as you move from left to right across a period. Since γ is below X in the same group, it would have a lower electronegativity compared to X, which is higher up in the periodic table.

The measurements in the table show a pattern based on a property of the second period elements in the periodic table.

What is the property?

• Atomic mass

• Electronegativity

• Ionisation energy

• Atomic radius

Answer explanation

The property that shows a pattern based on the measurements in the table for the second period elements (Li through Ne) with numbers ranging from 152 to 70 is Atomic radius.

As you move across the second period from lithium to neon, the atomic radius generally decreases. This is due to the increasing number of protons in the nucleus, which pulls the electron cloud closer to the nucleus, resulting in a smaller atomic radius. The other properties listed—atomic mass, electronegativity, and ionisation energy—do not show this specific decreasing trend across the period.

Data for the atomic number and electronegativity of five consecutive elements is listed in the table.

The electronegativity for the element with the atomic number 10 would be closest to which of the following?

• 0.00

• 3.50

• 4.10

• 4.50

Answer explanation

The electronegativity for the element with atomic number 10, which is neon, would be closest to 0.00. Neon is a noble gas with a complete outer electron shell, making it very stable and typically non-reactive. As a result, it has little tendency to attract electrons, so its electronegativity is very low, close to 0.

The first ionisation energies for five consecutive elements in the periodic table are

listed below.

Which element belongs to Group 7 of the periodic table?

• P

• Q

• R

• S