Substances with many covalent bonds
A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons. leads to the formation of substances with different types of structures, for example:
- small molecules, which contain a fixed number of The smallest part of an element that can exist. joined by covalent bonds
- giant covalent substances, which contain many atoms joined by covalent bonds
Learn more on properties of giant covalent compounds in this podcast.
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An example - Silicon dioxide
Silicon dioxide (often called silica) is the main A substance formed by the chemical union of two or more elements. found in sand. It is an example of a substance with a A structure in which very large numbers of atoms are joined together by covalent bonds in a regular network.. It contains many silicon and oxygen atoms. All the atoms in its structure are linked to each other by strong covalent bonds. The atoms are joined to each other in a regular arrangement, forming a giant covalent structure. There is no set number of atoms joined together in this type of structure.
High melting points and boiling points
Substances with giant covalent structures are solids at room temperature. They have very high The temperature at which a solid changes into a liquid as it is heated. and The temperature at which a substance rapidly changes from a liquid to a gas.. This is because large amounts of The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. are needed to overcome their strong covalent bonds to make them melt or boil.
Conduction of electricity
Most substances with giant covalent structures have no charged particles that are free to move. This means that most cannot To allow electricity, heat or other energy forms to pass through. electricity. Graphite, a form of carbon which can conduct electricity, is an exception.
Question
State three properties that are typical of substances with giant covalent structures.
They have high boiling points, high melting points and they cannot conduct electricity.