Free Periodic Properties and Trends MCQs with Answers

1. Across a period from left to right, the atomic radius of the elements generally

• A. decreases, because nuclear charge increases while electrons enter the same shell
• B. increases, because more electrons are added
• C. stays the same
• D. increases, because the nuclear charge decreases

Explanation: Each successive element adds one proton and one electron, but the electron enters the same outermost shell, so shielding hardly changes while the effective nuclear charge rises and the shell is pulled inwards. Down a group the opposite happens, since a whole new shell is added and radius increases. Atomic radius is the single trend from which ionisation energy and electronegativity mostly follow.

2. The first ionisation energy is the energy required to

• A. add one electron to a gaseous atom
• B. remove one mole of electrons from one mole of gaseous atoms, forming gaseous unipositive ions
• C. break one mole of covalent bonds
• D. convert one mole of a solid into a gas

Explanation: The definition specifies the gaseous state so that no lattice or intermolecular forces interfere, and it is always endothermic because an electron must be pulled away from an attracting nucleus. Adding an electron to a gaseous atom is electron affinity, the reverse process. Second ionisation energy is always larger than the first, since the electron is being removed from a positively charged ion.

3. Which element has the highest electronegativity?

• A. Oxygen
• B. Chlorine
• C. Fluorine
• D. Nitrogen

Explanation: Fluorine is the most electronegative element on the Pauling scale at 4.0, because it is small and has a high effective nuclear charge, so it attracts bonding electrons more strongly than any other atom. Oxygen at 3.5 is second and chlorine and nitrogen follow at 3.0. Electronegativity increases across a period and decreases down a group, so the maximum lies at the top right, excluding the noble gases.

4. Across a period, the first ionisation energy generally

• A. decreases, because atomic size increases
• B. increases, because the atoms get smaller and the nuclear charge increases
• C. remains constant
• D. decreases, because shielding increases sharply

Explanation: A greater nuclear charge acting on a shell at nearly constant distance holds the outer electrons more tightly, so more energy is needed to remove one. The trend is not perfectly smooth, dipping at boron and at oxygen because of the start of the p subshell and the first pairing of p electrons respectively. Those small irregularities are themselves strong evidence for subshell structure.

5. The oxides of the elements across period 3, from sodium to sulphur, change from

• A. acidic through amphoteric to basic
• B. acidic to neutral only
• C. basic through amphoteric to acidic
• D. neutral to basic

Explanation: Sodium and magnesium oxides are basic, aluminium oxide is amphoteric and reacts with both acids and alkalis, and the oxides of phosphorus and sulphur are acidic, dissolving to give acids. The change follows the shift from metallic to non metallic character across the period. Identifying aluminium oxide as the amphoteric turning point is the key fact.

6. Lithium shows a diagonal relationship with

• A. sodium
• B. magnesium
• C. beryllium
• D. aluminium

Explanation: Lithium resembles magnesium because their ions have similar size to charge ratios, so both form nitrides directly with nitrogen, both give carbonates that decompose on heating and both have oxides that are less soluble than those of their own group. Beryllium is diagonally related to aluminium in the same way. Diagonal relationships are strongest in the second and third periods.

7. The element with smallest value of ionization energy is

• A. Li
• B. Al
• C. Ca
• D. Ba

Explanation: Ionisation energy falls down a group as the outer electron lies further from the nucleus and is better shielded, and barium is the lowest of these four in the periodic table. Lithium is small and holds its outer electron tightly by comparison. Across a period the trend runs the other way, which is why aluminium is not the answer despite being a metal.