IB Chemistry The periodic table: classification of elements Practice Questions

Q: Which ion has the smallest radius: $\text{Na}^{+}$, $\text{Mg}^{2+}$ or $\text{Al}^{3+}$?

$\text{Al}^{3+}$. These ions are isoelectronic (10 electrons each). $\text{Al}^{3+}$ has the most protons (13), pulling the electrons in most strongly, so it is the smallest.

Q: Most metal oxides, such as $\text{Na}_{2}\text{O}$, dissolve in water to give solutions that are _____ (acidic or basic).

basic / alkaline. Metal oxides are basic; for example $\text{Na}_{2}\text{O}$ reacts with water to form $\text{NaOH}$, an alkali.

Question 1

Elements in the same group of the periodic table have the same number of:

Accepted Answer

Valence electrons. Elements in a group have the same number of valence (outer-shell) electrons, which gives them similar chemical properties.

Question 2

How does atomic radius change across a period from left to right?

Accepted Answer

It decreases. Across a period nuclear charge increases while electrons are added to the same shell, so the outer electrons are pulled in more strongly and atomic radius decreases.

Question 3

What happens to first ionisation energy across a period?

Accepted Answer

It generally increases. First ionisation energy generally increases across a period because increasing nuclear charge holds the outer electrons more tightly.

Question 4

How does the reactivity of group 1 metals change down the group?

Accepted Answer

It increases. Reactivity of group 1 metals increases down the group because the outer electron is further from the nucleus and more easily lost.

Question 5

How does the reactivity of group 17 (halogens) change down the group?

Accepted Answer

It decreases. Halogen reactivity decreases down the group because the larger atoms attract an extra electron less strongly.

Question 6

Which ion has the smallest radius: $	ext{Na}^{+}$, $	ext{Mg}^{2+}$ or $	ext{Al}^{3+}$?

Accepted Answer

$	ext{Al}^{3+}$. These ions are isoelectronic (10 electrons each). $	ext{Al}^{3+}$ has the most protons (13), pulling the electrons in most strongly, so it is the smallest.

Question 7

An element with the electron configuration $1s^{2}\,2s^{2}\,2p^{6}\,3s^{1}$ is found in period _____ of the periodic table.

Accepted Answer

3 / three. The highest occupied main energy level is $n=3$, so the element is in period 3 (it is sodium).

Question 8

Most metal oxides, such as $	ext{Na}_{2}	ext{O}$, dissolve in water to give solutions that are _____ (acidic or basic).

Accepted Answer

basic / alkaline. Metal oxides are basic; for example $	ext{Na}_{2}	ext{O}$ reacts with water to form $	ext{NaOH}$, an alkali.

Question 9

Going down group 17 from fluorine to bromine, the atomic radius increases. The main reason is

Accepted Answer

an increasing number of occupied electron shells. Additional occupied electron shells increase the distance of the outer electrons from the nucleus.

Question 10

Across a period from left to right, atomic radius generally

Accepted Answer

decreases. Increasing nuclear charge with electrons in the same shell pulls the electrons closer, decreasing radius across a period.

IB Chemistry: The periodic table: classification of elements — Practice Questions & Answers

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