Covalent Bonding (Edexcel IGCSE Chemistry)
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What is the difference between covalent bonds and ionic bonds?
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What is the difference between covalent bonds and ionic bonds?
In covalent bonds, the electrons are shared between atoms, while in ionic bonds, electrons are transferred from one atom to another.
What is represented by a short straight line between two atoms?
A short straight line between two atoms represents a covalent bond.
True or False?
Simple covalent molecules conduct electricity.
False.
Simple covalent molecules do not conduct electricity as they do not contain free electrons.
What is a covalent bond?
A covalent bond is a type of chemical bond where atoms share pairs of electrons with each other.
What are intermolecular forces?
Intermolecular forces are the weak forces of attraction that exist between individual molecules in a covalent substance.
True or False?
Covalent bonds involve the transfer of electrons.
False.
Covalent bonds involve sharing electrons, not transferring them.
What type of materials form a covalent bond?
The materials that form covalent bonds are non-metals.
Where is the strong electrostatic attraction in a covalent bond?
The strong electrostatic attraction in covalent compounds is between the shared pair of electrons and the nuclei of the atoms involved.
What makes each atom more stable in a covalent bond?
Sharing electrons in the covalent bond allows each atom to achieve an electron configuration similar to a noble gas.
What is formed when a group of two or more atoms covalently bond together?
A compound / molecule is formed when a group of two or more atoms covalently bond together.
Describe the forces of attraction in a covalent bond.
The attraction between a shared pair of electrons and nuclei.
True or False?
Dot and cross diagrams can represent giant covalent structures.
False.
Dot and cross diagrams are used to represent only small covalent molecules with a fixed number of atoms.
What are simple molecules?
A simple molecule is a small covalent molecule with a fixed number of atoms, such as H2, Cl2, H2O, NH3, and CH4.
What do dots and crosses represent in a dot and cross diagram?
In a dot and cross diagram, dots and crosses represents electrons.
What are diatomic molecules?
Diatomic molecules are molecules composed of two atoms, such as H2, Cl2, O2, and N2.
What are inorganic compounds?
Inorganic compounds are compounds that do not contain carbon AND hydrogen atoms, such as H2O and NH3.
Name three inorganic compounds that you should be able to draw dot-and-cross diagrams for.
Three inorganic compounds that you should be able to draw dot-and-cross diagrams for are:
Water
Ammonia
Carbon dioxide
What is the difference between simple covalent molecules and giant covalent structures?
Simple covalent molecules are small and can be separated into individual molecular units without breaking any chemical bonds.
Giant covalent structures are huge continuous networks of atoms that cannot be separated into individual units without breaking bonds.
True or False?
You can be expected to draw dot-and-cross diagrams for the the diatomic molecules hydrogen, oxygen, nitrogen, halogens and hydrogen halides.
True.
You can be expected to draw dot-and-cross diagrams for the the diatomic molecules hydrogen, oxygen, nitrogen, halogens and hydrogen halides.
What is an organic molecule?
An organic molecule is a simple molecule that contains carbon and hydrogen atoms, such as CH4, C2H6, and C2H4.
How many carbon atoms (at this level) can be included in dot-and-cross diagrams?
Up to 2 carbon atoms can be included in dot-and-cross diagrams (at this level).
So, diagrams for methane, ethane, ethene and similar compounds with halogen atoms.
True or False?
Simple molecular structures have high melting and boiling points.
False.
Simple molecular structures have low melting and boiling points.
What is the difference between covalent bonds and intermolecular forces?
Covalent bonds are strong bonds that hold atoms together within a molecule, while intermolecular forces are weak attractive forces that exist between different molecules.
True or False?
Covalent compounds are good conductors of electricity.
False.
Covalent compounds are poor conductors of electricity.
What are simple molecular structures?
Simple molecular structures are small molecules with covalent bonds, which have weak forces between the molecules (intermolecular forces).
What is the difference in melting / boiling point between simple molecular and giant covalent structures?
Simple molecular structures generally have low melting / boiling points, while giant covalent structures have high melting / boiling points.
Why are covalent compounds generally poor conductors of electricity?
Covalent compounds are generally poor conductors of electricity because they do not contain free ions or electrons to carry the current.
True or False?
Covalent bonds break when a covalent substance melts or boils.
False.
Intermolecular forces break when a covalent substance melts or boils..
What happens to melting and boiling points as the relative molecular mass of a substance increases?
As the relative molecular mass of a substance increases, the melting and boiling points also increase due to the increased number of electrons and stronger intermolecular forces.
What are insulators?
Insulators are materials that do not allow the flow of electric charge or heat, and common insulators include plastics, rubber, and wood.
Why do simple molecular structures have low melting and boiling points?
Simple molecular structures have low melting and boiling points due to weak intermolecular forces which require small amounts of energy to overcome.
True or False?
Simple molecular structures are often gases or liquids at room temperature.
True.
Simple molecular structures are often gases or liquids at room temperature.
What are giant covalent structures?
Giant covalent structures are macromolecules or giant lattices that consist of a huge number of non-metal atoms with strong covalent bonds in a fixed ratio.
Define allotropes.
Allotropes are different structural forms of the same element, such as diamond and graphite for carbon.
Why does diamond not conduct electricity?
Diamond does not conduct electricity because all of the outer shell electrons are held in the covalent bonds, and there are no freely moving charged particles to carry the current.
True or False?
Graphite is used in pencils, as an industrial lubricant, in inert electrodes, and in cutting tools.
False.
Graphite is used in pencils, as an industrial lubricant, in inert electrodes, and in locks.
Diamond is used in cutting tools.
What are fullerenes?
Fullerenes are a group of carbon allotropes that consist of molecules forming hollow tubes or spheres, such as C₆₀ (buckminsterfullerene or "buckyball").
Describe the structure of graphite
In graphite:
Each carbon atom is bonded to three others.
There are hexagonal layers.
There is one free / delocalised electron per carbon atom.
True or False?
Graphite is harder than diamond.
False.
Diamond is harder than graphite.
State the properties of diamond.
Diamond does not conduct electricity, has a high melting point, and is extremely hard.
What are the properties of graphite?
Graphite conducts electricity and heat, has a high melting point, and is soft and slippery.
True or False?
Fullerenes have a high surface area.
True.
Fullerenes have a high surface area.
Describe Buckminsterfullerene.
Buckminsterfullerene is a carbon allotrope with 60 carbon atoms forming a hollow sphere, also known as a "buckyball". Each carbon atom is bonded to three others and there is one free / delocalised electron per carbon atom.
Explain why graphite conducts electricity.
Graphite conducts electricity because it has delocalised electrons that can move / flow (throughout the structure)
Why is diamond hard?
Diamond is hard because its rigid, tetrahedral structure contains a lot of covalent bonds that require a large amount of energy to break.
Why is graphite soft?
Graphite is soft because there are weak intermolecular forces betwen the layers, which allows the layers to slide over each other.