Chemistry - Covalent Bonding (AQA)
Water is one of the three covalently bonded compounds that you need to know about, along with carbon dioxide and chlorine gas.

Chemistry - Covalent Bonding (AQA)

To do well in GCSE Science students should have a good understanding of the fundamental ideas in chemistry. This is the fourth of six quizzes aimed at reinforcing these ideas and it focusses on covalent bonding of atoms in compounds (molecules).

When elements react, atoms of each element join with atoms of other elements to form compounds. The atoms are held together by chemical bonds which can be either ionic or covalent. This quiz is all about covalent bonding. The three covalently bonded compounds that you need to know about in order to pass your exams are water, carbon dioxide and chlorine gas.

When covalent chemical bonding occurs, atoms of the elements involved share electrons. Electrons are shared in pairs and atoms can share more than one pair of electrons. When an atom has shared the exact number of electrons it requires, it will not be able to share with any other atoms. No electrons are lost or gained therefore covalent compounds do not contain ions, they are made up from molecules. This is very different to ionic compounds which are giant structures of ions.

Some molecules are very simple and consist of only two atoms, like the oxygen that we breathe. Others are incredibly large and complex for example, a single strand of human DNA is made up from around 200 billion atoms, all covalently bonded.

It is essential for the exam that you know the about atoms, molecules, elements and compounds. A lot of students are not sure how these are all related.

  • All matter is made from atoms
  • Molecules are made from covalently bonded atoms of non-metals
  • Non-metal elements are usually made from molecules
  • Metal elements are always made up from atoms, never molecules
  • Compounds are made from different atoms joined together
  • Compounds made from non-metal atoms joined together are always made of covalent molecules

Have a go at this quiz and see how well you understand covalent bonding.

Is salt covalently bonded?
Yes, because it is made from crystals
Yes, because it dissolves in water
No, because it is made from a metal joined to a non-metal
No, because it can be obtained from the ground
To answer correctly without guessing you need to know that salt is sodium chloride. Sodium is a metal so it can't possibly be covalently bonded
Which of the following represents a molecule of carbon dioxide?
Carbon dioxide is a linear molecule - all 3 atoms are in a line, with carbon in the middle
Which of the following would have covalent bonding?
A compound made from metals
A compound made from non-metals
An element made from metals
None of the above
Compounds of non-metals are always covalently bonded
How is a single covalent bond conveniently represented?
Two dots side by side
A short horizontal line between the symbols of the elements involved
A dot followed by a dash followed by a dot
A semi colon
A double covalent bond looks like an equals sign and a triple covalent bond is like an equals sign with an extra line underneath (or above!) it
Which of the following is not true about the compound carbon disulfide?
It is made from molecules
It is ionically bonded
It is covalently bonded
There are twice as many sulfur atoms as carbon atoms
You may never have heard of this compound but that doesn't matter. The name tells you enough to answer the question
Which of the following could have covalent bonding?
An alloy
Atoms of a metal
Atoms of a non-metal
Molecules of a non-metal
Only molecules have covalent bonding which immediately rules out the other answers
Which of the following word equations correctly represents a reaction in which covalent bonding occurs?
Hydrogen + oxygen → water
Carbon + dioxide → carbon dioxide
Sulfuric acid + zinc → hydrogen + zinc sulfate
Chlorine + chlorine → dichlorine
Only the first and the third word equations are correct and since the third one involves a metal, it must have ionic bonding
Why is the bonding in chlorine gas covalent?
Chlorine gas is made from molecules
Chlorine is an element
Chlorine is a halogen
Chlorine is a non-metal
All of the statements about chlorine are true. You may have chosen option 1 as you know molecules are always covalently bonded but that doesn't answer the question. The only option that answers 'why' is the fact that it is a non-metal
Chlorine has seven electrons in its outer energy level (shell). Six of these are arranged in pairs with one on its own. How many covalent bonds can it form?
Only electrons that are not already part of a pair can be shared
What is a single covalent bond?
One pair of shared electrons
Two pairs of shared electrons
One electron shared between two atoms
Four electrons shared between two atoms
The second option describes a double covalent bond
You can find more about this topic by visiting BBC Bitesize - Giant covalent molecules - AQA

Author:  Kev Woodward

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