Covalent Bonding Flashcards
What are covalent bonds?
When non-metal atoms share electrons with other non-metal atoms to obtain a full outer shell of electrons
Are covalent bonds between atoms strong or weak?
Covalent bonds between atoms are very strong
What is formed when two or more atoms are covalently bonded together?
When two or more atoms are covalently bonded together, they form ‘molecules’
What exists between individual molecules? And are they weaker or stronger than covalent bonds?
Weak intermolecular forces exist between individual molecules. These forces are much weaker than covalent bonds.
What are shared electrons called and how do they occur?
Shared electrons are called bonding electrons and occur in pairs
What are electrons on the outer shell which are not involved in the covalent bond(s) called?
Electrons on the outer shell which are not involved in the covalent bond(s) are called non-bonding electrons
Do simple covalent molecules electricity why or why not?
Simple covalent molecules do not conduct electricity as they do not contain free electrons. No free delocalised electrons
Explain the electrostatic attraction between covalent bonds
There is a strong electrostatic attraction between the shared pair of electrons and the nuclei of the atoms involved, since the electrons are negatively charged and the nuclei are positively charged
What should covalent bonds be regarded as and why?
Covalent bonds are best regarded as charge clouds, due to the fact that the electrons are in a state of constant motion.
What structures do covalent bonds tend to have and give examples?
Covalent substances tend to have small molecular structures, such as Cl2, H2O or CO2
Describe simple molecular structures
Simple molecular structures have covalent bonds joining the atoms together, but intermolecular forces that act between neighbouring molecules
They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules
These forces are very weak when compared to the covalent bonds and so most small molecules are either gases or liquids at room temperature
Often the liquids are volatile
Why do simple molecular structures have low melting and boiling points?
They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules
Why are most small molecules either gases or liquids at room temperature?
They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules
These forces are very weak when compared to the covalent bonds and so most small molecules are either gases or liquids at room temperature
What happens as the molecules increase in size?
As the molecules increase in size the intermolecular forces also increase as there are more electrons available
This causes the melting and boiling points to increase
Describe what happens as the relative molecular mass of a substance increases?
An increase in the relative molecular mass of a substance means that there are more electrons in the structure, so there are more intermolecular forces of attraction that need to be overcome when a substance changes state
So larger amounts of heat energy are needed to overcome these forces, causing the compound to have a higher melting and boiling point
Why are covalent compounds poor conductors of electricity?
They are poor conductors of electricity as there are no free ions or electrons to carry the charge
Most covalent compounds do not conduct at all in the solid state and are thus insulators
What happens when a covalent molecule melts or boils?
When a covalent molecule melts or boils the covalent bonds do not break, only the intermolecular forces.
What differs simple molecules to giant covalent structures?
simple molecules contain fixed numbers of atoms
Giant covalent structures on the other hand have a huge number of non-metal atoms bonded to other non-metal atoms via strong covalent bonds
Fill in the blanks - giant lattices and have a - - of atoms in the overall structure
Giant lattices and have a fixed ratio of atoms in the overall structure
Fill in the blanks - Diamond, graphite and C60 Fullerene are - of carbon
Diamond and graphite are allotropes of carbon
What are allotropes?
Different atomic or molecular arrangements of the same element in the same physical state.
Why aren’t diamond and graphite the same?
Both substances contain only carbon atoms but due to the differences in bonding arrangements they are physically completely different
Describe the structure of a diamond
In diamond, each carbon atom bonds with four other carbons, forming a tetrahedron. All the covalent bonds are identical, very strong and there are no intermolecular forces
Physics properties of diamond
It does not conduct electricity
It has a very high melting point
It is extremely hard and has a density of 3.51 g / cm3 – a little higher than that of aluminium
Why is diamond very hard?
In diamond, each carbon atom bonds with four other carbons, forming a tetrahedron. The four covalent bonds are very strong and extend in a giant lattice, so a very large amount of heat energy is needed to break the lattice - this makes it very hard.
What is diamond used in?
Diamond is used in jewellery and for coating blades in cutting tools
The cutting edges of discs used to cut bricks and concrete are tipped with diamonds
Heavy-duty drill bits and tooling equipment are also diamond tipped
What state are giant covalent molecules in at room temperature and why?
Giant covalent molecules are always solids at room temperature.
•Giant covalent molecules have millions of strong covalent bonds.
They always have high melting and boiling points. This means a lot of energy is required to break them.
Can diamonds conduct electricity why or why not?
•Diamond cannot conduct electricity.
• There are no free electrons to carry electrical charge.
What is the melting point of diamond?
Over 3,700^oC
Explain, in terms of electrostatic attractions, what is meant by a covalent bond.
The attraction between shared pairs of electrons; [1 mark]
And the nuclei of two / both atoms (in the bond)
What is silicon (IV) oxide/silicon dioxide?
Silicon(IV) oxide (also known as silicon dioxide or silica), SiO2, is a giant covalent compound.
Silicon dioxide occurs naturally as what?
It occurs naturally as sand and quartz
Describe the atoms in silicon dioxide
Each oxygen atom forms covalent bonds with 2 silicon atoms and each silicon atom in turn forms covalent bonds with 4 oxygen atoms
What is the form of silicon dioxide?
A tetrahedron is formed with one silicon atom and four oxygen atoms, similar to diamond
Describe the forces within silicon dioxide
SiO2 has lots of very strong covalent bonds and no intermolecular forces so it has similar properties to diamond
How is silicon dioxide similar to Diamond?
It is very hard, has a very high boiling point, is insoluble in water and does not conduct electricity
What are some of the properties of silicon dioxide?
It is very hard, has a very high boiling point, is insoluble in water and does not conduct electricity
Is silicon dioxide cheap or expensive and why?
SiO2 is cheap since it is available naturally and is used to make sandpaper and to line the inside of furnaces
Describe the atoms in graphite
Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom. These free electrons migrate along the layers and are free to move and carry charge, hence graphite can conduct electricity.
Why can graphite conduct electricity?
Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom
These free electrons migrate along the layers and are free to move and carry charge, hence graphite can conduct electricity
Why is graphite soft and slippery?
The covalent bonds within the layers are very strong, but the layers are attracted to each other by weak intermolecular forces, so the layers can slide over each other making graphite soft and slippery.
Describe the bonds in graphite
The covalent bonds within the layers are very strong, but the layers are attracted to each other by weak intermolecular forces, so the layers can slide over each other making graphite soft and slippery.
What are the physical properties of graphite?
It conducts electricity and heat
It has a very high melting point
It is soft and slippery and less dense than diamond (2.25 g / cm3)
What is graphite used for?
It is used in pencils and as an industrial lubricant, in engines and in locks
It is also used to make inert electrodes for electrolysis, which is particularly important in the extraction of metals such as aluminium
What are fullerenes?
Fullerenes are a group of carbon allotropes which consist of molecules that form hollow tubes or spheres
What are some functions of fullerenes?
Fullerenes can be used to trap other molecules by forming around the target molecule and capturing it, making them useful for targeted drug delivery systems
They also have a huge surface area and are useful for trapping catalyst molecules onto their surfaces making them easily accessible to reactants so catalysis can take place
What is the structure of c60 fullerene?
C60 fullerene has a simple molecular structure.
Describe the forces in c60 fullerene
In c60 fullerene, there are c60 molecules with weak intermolecular forces between them.
What are the properties of c60 fullerene?
C60 fullerene has lower melting and boiling points than diamond and graphite.
C60 fullerene is not as hard as diamond.
C60 fullerene does not conduct electricity
Explain why C60 Fullerene has a lower melting and boiling point than diamond and graphite.
When fullerene is melted, only the relatively weak intermolecular forces of attraction must be broken. This does not require as much energy as breaking all the strong covalent bonds when diamond and graphite are melted.
Explain why C60 Fullerene is not as hard as diamond
It does not take as much energy to break the intermolecular forces of attraction in C60 Fullerene compared to breaking the strong covalent bonds in diamond.
Explain why C60 Fullerene does not conduct electricity
Although all the carbon atoms in
C60 only form three bonds, the fourth electron on each atom can only move around within each C60 molecule; the electrons cannot jump from molecule to molecule.
