Topic 7 - Types of Substances Flashcards
1.32 - What different structures and bonding are used to describe ionic substances?
Where found - Compounds containing a metal and a non-metal.
Bonding - Formed by the exchange of electrons making oppositely charged ions attracting one another.
Structure - Billions of ions held together in a lattice structure.
Properties - High boiling and melting points, soluble in water and can conduct electricity when aqueous but not when solid.
1.32 - What different structures and bonding are used to describe simple molecular substances?
Where found - Compounds and elements containing a non-metal
Bonding - Covalent bonds formed when atoms share a pair or more of electrons.
Structure - Small and distinct groups of atoms.
Properties - Low melting and boiling points, some are soluble in water and most don’t conduct electricity.
1.32 - What different structures and bonding are used to describe giant covalent substances?
Where found - Few non-metal elements and some compounds of non-metals.
Bonding - Covalent bonds formed when atoms share a pair or more of electrons.
Structure - Billions of atoms held together in a lattice structure.
Properties - High boiling and melting points, insoluble in water and most don’t conduct electricity. ( Except graphite )
1.32 - What different structures and bonding are used to describe metallic substances?
Where found - All metals.
Bonding - Electrostatic attraction between positive metal ions and the sea of delocalised electrons.
Structure - Billions of ions held together in a giant lattice structure of positive electrons surrounded by a sea of negative delocalised electrons
Properties - High boiling and melting points, insoluble in water and conduct electricity when solid and liquid.
1.33 - Explain the properties of ionic compounds
High melting and boiling points as the electrostatic force of attraction between the oppositely charged ions are strong, so a lot of energy is required to overcome these forces and separate the ions. Ions with higher charges will need more energy to overcome the forces of attraction.
Ionic compounds conduct electricity when aqueous as the charged particles which can carry electricity are free to move so it can pass on the current. When solid, the ions cannot move from place to place.
1.33 - What are the two ions?
Cations - Positively charged ions attracted to the negatively charged anode.
Anions - Negatively charged ions attracted to the positively charged cathode.
1.34 - Explain the properties of simple covalent molecular compounds?
Low boiling and melting points due to weak inter-molecular forces meaning low energy required to overcome these forces.
Poor conductors of electricity as simple molecules have no charge so can’t carry an electric current. In a covalent bond, the strong forces between negative electrons and the positive nuclei hold the electrons in place so can’t move to carry an current.
1.35 - What are some giant covalent carbon allotropes?
Graphite
Diamond
1.36 - Describe the structures of graphite and diamond
Graphite and diamond both have a giant covalent lattice.
Graphite has three covalent bonds for each carbon atom although diamond has four bonds.
Graphite has a layered hexagonal structure but diamond has a tetrahedral structure.
Graphite has a free bond meaning it has delocalised electrons and conducts electricty, while diamond has no free bonds and can’t conduct electricity.
There are weak forces of attraction between the sheets of carbon in graphite but in diamond there are strong covalent bonds.
1.37 - Explain the uses of graphite and diamond
Graphite is used as a lubricant as there are weak forces of attraction between the layers of carbon meaning the layers can easily slide past each other making it soft.
Diamond is used in cutting tools as it has a rigid network of carbon atoms joined by strong covalent bonds making it a useful tool.
It is also an electrical insulator as it has no free delocalised electrons.
1.38 - Explain the properties of fullerenes and graphene
C60/Buckministerfullerene molecule have 60 carbon atoms, each carbon atom is bonded to three other carbon atoms.
They have weak intermolecular forces so low melting points and these forces make it soft and slippery. However, the molecules are very strong due to the strong covalent bonding between atoms.
Graphene is a giant covalent structure with sheets of carbon atoms which are one atom thick making it light.
It has strong covalent bonds between the atoms making it strong.
Every carbon is bonded to three other carbons so there are free electrons to move making it a good conductor.
1.39 - Explain what polymers are
Polymers like polyethene is made up of monomers of ethene. Monomers are small molecules that join to become a polymer.
Longer polymers have stronger intermolecular forces compared with shorter polymers as more molecules. Longer polymers therefore have higher melting points.
1.40 - Explain the properties of metals
They are malleable, meaning that they are able to be changed shape without shattering, this is done as the layers of ions slide over each other and the sea of electrons hold these ions in together so the metal doesn’t shatter.
They can conduct electricity as when a voltage is applied to both sides of a metal, electrons flow to the positive terminal, carrying energy forming an electrical current. As the charge of a metal increased, the delocalised electrons increase so electrical conductivity increases.
1.41 - Describe the limitations of bonding models
The Dot and cross model shows how many electrons are shared in covalent bonds although it doesn’t show the actual atomic structure and suggests that electrons in different atoms are different, but they are the same.
The Metallic model shows the metal ions in a lattice and explains how electricity is conducted, however it doesn’t show the ions vibrating all the time.
The Ball and stick show which atoms are joined together and the shape of the structure, but the atoms are too far apart and the atoms are held together by sticks.
1.42 - What are the properties of most metals?
When solid:
High melting points
Shiny when polished
Malleable
High density
Good conductors of electricity
