SC5/6/7: Bonding & Types of Substances Flashcards
SC5c Properties of Ionic Bonds
Describe the properties of Ionic Bonds
1. High Melting/Boiling Point - The electrostatic forces of attraction between oppositely charged ions are strong.
- Alot of energy is required to overcome these forces, meaning it will have a high boiling/melting point.
2. Electrical Conductivity - Ionic compounds conduct electricity when they are dissolved or molten. This is as the 2 conditions for a substance to conduct electricity are;
- It must contain charged particles
- These particles must be free to move.
SC7a Molecular Compounds
Describe the properties of Covalent Bonds.
1. Melting and Boiling point - While the covalent bonds themselves in a molecule are strong forces of attraction,
- There are also weak intermolecular bonds between molecules, this is why simple molecules have low boiling points.
2. Conduction of Electricity - An electric current is a flow of charged particles. Covalent Bonds don’t form charged particles and the strong bonds between the electrons and nuclei hold them in place, the electrons cannot flow and so cannot carry charge.
SC7a Molecular Compounds
Describe what Polymers are?
1. Monomers are small, simple molecules that can be joined together to form a polymer.
- Monomers are usually linked by covalent bonds.
- Most polymers contain a chain of carbon atoms.
2. Poly(ethen) or polythene is a polymer made of ethen monomers.
3. Longer polymers have more intermolecular forces between them. The longer chains also tend to get tangled up.
- For these reasons longer polymers have higher melting points.
SC7b Allotropes of Carbon
Describe the general properties of Giant Covalent compounds.
1. High melting/boiling point - Giant Covalents are solids at room temp, Covalent bonds are strong so alot of energy is required to break them.
2. Conduction of Electricity - as Giant Covalents have no overall charge, they cannot conduct Electricity ( apart from graphite ).
3. Insoluble in water - A substance can dissolve in water if it forms strong enough bonds with water molecules.
- Giant covalent substances cannot form these strong attractions with water, so they are insoluble.
SC7b Allotropes of Carbon
Describe the properties of;
A) Fullerens
B) Graphene
A) Properties of Fullerenes include;
- They are bonded to 3 other carbon atoms.
- They can either be nanotubes or spherical.
- Nanotubes; high tensile strength, resist being stretched, conduct electricity ( delocalised electrons ).
- Buckyballs ( Spherical ); These are simple molecules, weak intermolecular forces, slippery and have low melting points. They can only conduct electricity across their surface
B) Properties of Graphene include;
- Resembles a single layer of Graphite.
- Very high melting point & strong due to regular arrangement of carbon atoms.
- Conducts electricity due to delocalised electrons.
- ( Carbon has 4 outer shell electrons, 3 electrons are used in bonding with other carbons, leaving 1 free electron )
SC7b Allotropes of Carbon
Describe the properties and uses of;
A) Diamond
B) Graphite
A) Properties of Diamond include;
- Each carbon atom is joined to 4 other carbon atoms via covalent bonds.
- The carbon atoms forms a regular rigid tetrahedral network structure.
- There are no free electrons, meaning it cannot carry charge.
- Very high melting/boiling point, strong covalent bonds.
- Uses; Rigid network makes diamond good for cutting tools ( drill bits ), can also be used as electrical insulator.
B) Properties of Graphite include;
- Each carbon atom is bonded to 3 other carbon atoms.
- Carbon atoms form a hexagonal layered network structure.
- Layers have weak forces between them and can slide over each other.
- Since the layers can move and have delocalised electrons Graphite can carry charge.
- Uses; Weak forces on layers makes it good lubricant, can also be used for electrodes in battieries.
SC7c Properties of metals
Describe the common properties of;
A) Metals
B) Non-Metals
A) Properties of Metals include;
- Shiny
- High melting points
- Good electrical conductors
- Good heat conductors
- High density
- Malleable
B) Properties of Non-Metals include;
- Dull
- Low melting points
- Poor conductors of electricity
- Low density
- Brittle
SC7c Properties of metals
Describe Metallic Bonding and the properties of Metal.
1. Outer shell electrons are lost from each atom and become free to move throughout the metal ( delocalised ).
- This leaves a giant lattice of positive metal ions surrounded by ‘sea’ of delocalised electrons.
- Metallic bonding is the attaction between this positive giant lattice and the ‘sea’ of delocalised electrons.
2. Malleable - This means they can be hammered into shape. This is because when you hit a metal the layers of ions slide over each other. The ‘sea’ of electrons hold the metal together, so they bend instead of breaking.
3. Conducting Electricity - Delocalised electrons move randomly between positive metal ions in all directions, when a voltage is applied between 2 points on a metal, electrons flow towards to positive side.
- This flow of electrons transfers energy and forms a current.
SC7d Bonding models
Describe the limitations of the;
A) Dot and cross model
B) Metallic Model
C) 3D Ball and Stick Model
A) Dot and cross diagrams do not show the strucure formed and they suggest that the electrons in different atoms are different, when they are the same.
B) Metallic model does not show that ions will be vibrating all the time.
C) The 3D ball and stick model shows the atoms to far apart and there not really ‘sticks’ holding the atoms together.
