Structure and bonding

What are the properties of a giant ionic lattice?

• 3D structures

• very strong forces of attraction between the positive and negative ions

• called electrostatic forces of attractions

• which hold the positive and negative ions in place

What are the properties of ionic compounds?

• very high melting and boiling points

• as the strong electrostatic forces of attraction

• require a lots of energy to overcome

When ionic compounds conduct electricity…

ions move

What happens in ionic bonding?

• when a metal reacts with a non metal

• outer electrons are transferred from the metal to non metal

What are isotopes?

• atoms with the same number of protons

• but different number of neutrons

What are the properties of small covalent molecules?

• low melting and boiling points

• so they are usually gases or liquids at room temp

Why do small covalent molecules have low melting and boiling points?

• atoms are held together by strong covalent bonds

• there are very weak intermolecular forces between each molecule

• so the intermolecular forces don’t require a lot of energy to break

• and covalent bonds are not broken when a substance melts or boils

What happens as you increase the size of the covalent molecules?

• intermolecular forces increase

• so their boiling point increases

• as the intermolecular forces require more energy to break

Why don’t small covalent molecules not conduct electricity

small covalent molecules don’t have an overall electric charge

…are always solids at room temp

Giant covalent structures

What’s the structure of diamond?

each carbon atom forms covalent bonds to 4 other carbon atoms

Why is diamond hard?

• huge number of carbon atoms joined by covalent bonds

Why can’t diamond conduct electricity?

• all of the outer electrons are in covalent bonds

• so there are no delocalised elctrons to carry charge

What’s the structure of graphite?

• Giant covalent structure

• forms covalent bonds to 3 other carbon atoms

• carbon atoms form hexagonal rings

• that are arranged into layers

• no covalent bonds between the layers

• so the layers can slide over each other

What are the properties of graphite?

• soft and slippery

• very high metling and boiling point

• good conductor of electricity

• good conductor of heat

What makes graphite soft and slippery?

• atoms are arranged into layers

• no covalent bonds between the layers

• so the layers can slide over each other

Why is graphite a good conductor of electricity and heat

• delocalised electrons inbetween layers can move

• so they can conduct electricity and thermal energy

Why is graphene a good conductor of electricity?

• has delocalsied electrons

• which can move through the graphene molecule carrying an electrical charge

Why is graphene strong and have a high melting and boiiling point?

• large number of strong covalent bonds

• which require a lot energy to break

What are the structures of fullerenes

• carbon atoms with hollow shapes

• usually hexagonal rings of carbon atoms

How many carbon atoms does a Buckminister fullerene contain?

60

What are the different uses of fullerenes?

• can be used to deliver drugs into the body

• can be used as lubricants to reduce friction between moving parts in machines

• can be used as catylysts to speed up chemical reactions

What are carbon nanotubes?

• fullerenes shaped into long cylinders

• with a relatively small diameter

• have a very high length to diameter ratio

What are the properties of carbon nanotubes?

• high tensile strength

• have delocalised electrons

• so good conductors of electricity

• good confuctors of heat

What is one use of carbon nanotubes?

• to reinforce materials

What are polymers?

• very large molecules

• all the covalent bonds are very strong

Why are most polymers solids at room temp?

• intermolecular forces ares strong

• so it takes a lot energy to break

• so they have a high melting point

• so they are solids at room temp

What are the structures of metals?

• electrons in the outer shell are delocalised

• so between the sea of delocalised negative electrons and the positive metal ions, there is a strong electrostatic force of attraction

• which are strong

Why do metals have high melting and boiling points?

• it takes a lot of energy to break the strong metallic bonds

Why can metals bend and change shape?

• the layers of atoms can slide over each other

What is an alloy?

• a mixture of metals

• where the different sizes of atoms distorts the layers

• making it more difficult for the layers to slide over each other

• so alloys are harder than pure metals

What are the disadvantages with a 2D stick diagrams?

• you can’t tell which electron in the covalent bond came from which atom

• don’t show idea of outer electrons that are not in bonds

• don’t give accurate info on the shape of the molecule

What is the advantage with a 3D stick diagram?

• it shows the shape of the molecule

What is the advantage of a ball and stick diagram?

you can clearly see the ions in 3 dimensions

What is the disadvantage of a ball and stick diagram?

ions are shown as widely spaced when the ions are close together

What is the problem with the atom diagrams?

they only show a tiny part of the giant structure