Simple molecules and covalent bonds

Which molecule has three pairs of electrons shared between two of its atoms?

May/June 2015

Which compound has exactly eight covalent bonds?

May/June 2015

Which molecules contain at least one double covalent bond?

May/June 2015

Which compound has exactly eight covalent bonds?

May/June 2015

The sulfur isotopes are $^{32}_{16}\text{S}$ and $^{33}_{16}\text{S}$.

May/June 2015

The phosphorus isotopes shown are $^{31}_{15}\text{P}$ and $^{32}_{15}\text{P}$.

May/June 2015

Which dot-and-cross diagram, with every outer-shell electron for each atom shown, is incorrect?

May/June 2016

Ethene, $\text{C}_2\text{H}_4$, is a covalent compound that has a simple molecular structure. Which of the following statements about ethene is correct?

May/June 2016

Which row gives the correct comparison between carbon dioxide and methane?

May/June 2017

Among the molecules shown, how many have only a single covalent bond? $\text{Cl}_2$ \quad $\text{H}_2$ \quad $\text{HCl}$ \quad $\text{N}_2$ \quad $\text{O}_2$

May/June 2017

Among the molecules shown, how many contain just one covalent bond? $\text{Cl}_2$, $\text{H}_2$, $\text{HCl}$, $\text{N}_2$, $\text{O}_2$

May/June 2017

Ethane, $\text{C}_2\text{H}_6$, and ammonia, $\text{NH}_3$, are covalent compounds. Their dot-and-cross diagrams are shown. Which of the following statements are correct?

May/June 2018

Ethane, $\text{C}_2\text{H}_6$, and ammonia, $\text{NH}_3$, both are covalent compounds. Their dot-and-cross diagrams are displayed. Which statements are true?

May/June 2018

How many shared pairs of electrons are present in an ammonia molecule?

May/June 2019

How many pairs of electrons are shared in a single carbon dioxide molecule?

May/June 2019

The dot-and-cross diagram shows compound X. Which of the following statements about compound X is correct?

May/June 2021

What do we mean by a covalent bond?

May/June 2021

Which dot-and-cross diagram correctly represents an ethene molecule?

May/June 2021

Which dot-and-cross diagram shows carbon dioxide? Only electrons in the outer shell are shown.

May/June 2022

The dot-and-cross diagram shows one molecule of tetrafluorosilane, $\text{SiF}_4$. Only the electrons in the outer shell are included. Which statement is correct?

May/June 2022

Ethane, $\text{C}_2\text{H}_6$, and ammonia, $\text{NH}_3$, are covalent compounds. The dot-and-cross diagrams for these compounds are displayed. Which statements are true?

May/June 2023

Which molecule contains the greatest number of electrons participating in covalent bonds?

May/June 2023

Which molecule contains just four electrons participating in covalent bonds?

May/June 2024

The structural formula of a sulfuric acid molecule is shown. How many electrons take part in forming all the covalent bonds in one molecule?

Oct/Nov 2015

The structural formula of sulfuric acid is shown. How many electrons are used in total to form all the covalent bonds in one molecule?

Oct/Nov 2015

Some students made three claims about the bonding in a molecule of ammonia, $\text{NH}_3$. 1. Because a nitrogen atom has three outer electrons, every outer electron takes part in bonding. 2. A nitrogen atom has five outer electrons, so two of its outer electrons are not used in bonding. 3. A nitrogen atom shares electrons with each of the three hydrogen atoms. Which of these statements about bonding in ammonia are correct?

Oct/Nov 2016

As substance Q changes from solid to liquid, only the weak forces of attraction between its molecules are overcome. Which row gives the correct description of Q?

Oct/Nov 2016

Buckminsterfullerene has the chemical formula $\text{C}_{60}$. Which description best fits the structure of buckminsterfullerene?

Oct/Nov 2016

What does the dot-and-cross diagram for $\text{NCl}_3$ show?

Oct/Nov 2018

The diagram depicts part of the Periodic Table. Which two letters show elements that are able to react with each other to make covalent compounds?

Oct/Nov 2018

The diagram illustrates the covalent bonds present in an organic compound. The overall number of electrons in one molecule of this compound is .....X..... . The overall number of electrons in the bonds in one molecule of this compound is .....Y..... . Which numbers correctly fill gaps X and Y?

Oct/Nov 2020

The diagrams below show part of the structures of carbon dioxide and calcium carbide. The carbon dioxide molecules are displayed as O=C=O. Calcium carbide is represented as a lattice of Ca$^{2+}$ ions and C$_2^{2-}$ ions.

Oct/Nov 2020

The diagram illustrates a section of the Periodic Table. Which two letters show elements that are able to react with each other to make covalent compounds?

Oct/Nov 2021

The bonding in a carbon dioxide molecule may be shown using a dot-and-cross diagram. Which diagram is the correct one?

Oct/Nov 2021

The diagram illustrates a section of the Periodic Table. Which two letters show elements that can react with each other to make covalent compounds?

Oct/Nov 2021

Which compound contains the greatest number of single bonds in a single molecule?

Oct/Nov 2022

Which two pairs of atoms are joined by an equal number of bonds?

Oct/Nov 2022

Boron trifluoride, $\text{BF}_3$, is a simple molecule. Each $\text{BF}_3$ molecule contains three covalent bonds. Every one of these bonds is formed by the sharing of one electron from the boron atom and one electron from a fluorine atom. What is unusual about the bonding in boron trifluoride?

Oct/Nov 2022

Carbon dioxide is a gas at room temperature.

Oct/Nov 2022

Which two molecules contain an equal number of electrons in covalent bonds?

Oct/Nov 2024

Fig. 6.1 presents the structures of boron nitride and hydrazine.

Oct/Nov 2024

The structure of hydroxylamine, $\mathrm{NH_2OH}$, is shown. Which row correctly describes hydroxylamine?

Oct/Nov 2025

This question concerns the covalent compound hydrogen peroxide. Fig. 6.1 shows the displayed formula H-O-O-H.

Oct/Nov 2025