Bonding Flashcards
What are the 3 types of bonds?
Ionic bonds
Covalent bonds
Metallic bonds
When does ionic bonding occur?
Between a metal and non-metal
When are positive and negative ions created?
Positive ions are created when an atom LOSES electrons
Negative ions are created when an atom GAINS electrons
How is ionic bonding shown in a diagram?
Dot and cross diagram
Transfer of electrons (dot/cross) between outer shells of two atoms shown through arrows
Must show two stages of process: one showing transfer and other showing result
What are ionic compounds held together by?
The attraction between oppositely charged ions/electrostatic forces/ionic bonds (all the same)
What do all ionic compounds exist as?
Giant ionic structures - Many ions joined to each other with ionic bonds in a giant ionic lattice
What are the properties of ionic compounds?
Generally soluble - Water molecules are attracted to charged ions
High mpt and bpt - Strong bonds between oppositely charged ions are hard to break
Do not conduct electricity when solid - Ions firmly held together in lattice (+ no free electrons)
Do conduct electricity when molten - Ions are free to move
Why is the melting temperature higher on a compound containing ions with higher charges?
The higher the charges on ions are in an ionic compound, the stronger the forces of attraction are, therefore making them harder to break
When does covalent bonding occur?
Between two non-metals
What happens in ionic bonding?
Electrons are transferred between atoms to create a full outer shell and become ions
What happens in covalent bonding?
Two ions (either different or the same) share electrons to achieve a full outer shell
How is covalent bonding shown?
In one diagram in which the shared electrons are depicted between the two ions
Why are covalent bonds strong?
The shared electrons are attracted to the nuclei of both atoms
What do most covalently bonded structures exist as?
Simple molecular structures
What forces of attraction are present in substances with a simple molecular structure?
Strong covalent bonds between atoms (intramolecular forces), but weak intermolecular forces (forces of attraction between individual molecules - hence low mpt and bpt)
What properties do simple molecular structures have?
Low mpt and bpt - Liquids and gases at room temp
Do not conduct electricity - No delocalised electrons
Which covalent substances exist as giant structures?
Diamond + Graphite
What properties does graphite have?
Very soft
Conducts electricity - sea of free moving electrons because fourth electron is unbonded
Very high mpt - Over 3600 degrees
Describe the structure of graphite
Made of C atoms
Layers of hexagonal structures
Each C atom joined to 3 others
Fourth electron is delocalised between layers
Strong covalent bonds between C atoms but weak forces of attraction between layers
What are the uses of graphite?
Pencils + lubricants - Layers can slide because of weak forces of attraction
Electrodes
Describe the structure of diamond?
A form of C
Each C atom is joined to 4 others
What are the properties and uses of diamond?
V. hard -> Cutting tools
V. high mpt + bpt
Crystalline -> Jewellery
Does not conduct electricity
What are metallic bonds?
Forces of attraction between positive metal ions and delocalised electrons
Describe metallic structures
Giant structures of regularly arranged metal atoms in a lattice in a ‘sea’ of delocalised electrons which are free to move around the lattice
Why do metallic structures have delocalised electrons?
All electrons from the outer shells of the metals are delocalised (made to not belong to a particular atom)
What are properties of metals?
Good conductors of electricity - Delocalised electrons
Malleable/ductile - Metal ions can slide over each other
High mpt and bpt (generally) - Exist as giant structures
Why are melting + boiling temperatures different on different metals?
The higher the charge on the metal ion the more delocalised electrons there are (because they will have needed to lose more to achieve a full outer shell), so the stronger the metallic bonds
What are the differences between single, double and triple covalent bonds?
Double and triple covalent bonds are stronger and therefore require more energy to break them
What is an alloy?
A combination of 2+ elements, where at least 1 is a metal
What makes alloys different to pure metals?
The ions of the different elements are different sizes which makes it harder for the layers to slide across each other when a force is applied - layers are distorted
This also makes them stronger then pure metals
What is graphene?
A single layer of graphite, just one atom thick
What properties does graphene have?
Very light - Only 1 atom thick
Very strong - Covalent bonds between atoms
Can conduct electricity - Has delocalised electrons
What are the uses of graphene?
Graphene makes materials stronger without making them much heavier.
It can be used in solar panels, batteries etc.
What are fullerenes?
Cage structures made from carbon atoms
Most famous is buckminsterfullerene (bucky balls) which are spherical molecules containing 60 carbon atoms (formula: C60)
What uses do fullerenes have?
Catalysts
Lubricants
Vehichles for transporting drugs into the body (because they are spherical they can enclose other molecules)
What are carbon nanotubes?
Single layers of graphite (graphene) rolled into a tube
They are cylindrical fullerenes
What could carbon nanotubes be used for in the future?
To make miniature electronic circuits
When is something considered to be nano-sized?
When it is between 1-100nm (nanometres)
What are the benefits of nanoparticles?
They have a very high surface area to volume ratio, meaning smaller amounts of materials can be used for a purpose compared to using normal sized particles.
This makes them cheaper and more efficient to use than larger particles.
What are the drawbacks to nanoparticles?
They are still a relatively new area of research so there could still be long-term effects to human health that we don’t know about
Why are nanoparticles different to normal particles?
When materials are produced as nano-sized particles they behave differently to the same material on bulk scale
E.g. ‘normal’ gold particles are extremely unreactive, but gold nanoparticles can be very efficient catalysts for many processes because of their higher surface area
What are nanoparticles used as?
Catalysts - Larger surface on which reactions can be catalysed
Medicine - Fullerene nanoparticles can be used to efficiently deliver drugs to a specific area of the body to target a disease.
Electronics - Carbon nanotubes are used in new computer chips because of their good electrical conductivity.
Cosmetics - So small that visible light passes through them, making them transparent so white substances, like sun cream, can be made transparent
Deodorants - Nanoparticles can have antimicrobial properties
What are smart materials?
Materials with properties that react to a change in their environment. These changes are reversible.
What are thermochromic materials?
React to a change in temp by changing colour
E.g.
Thermometers made of plastic strips
Baby feeding spoons
What are photochromic materials?
React to a change in light by changing colour
E.g.
Lenses for sunglasses
What are shape memory alloys/polymers?
Regain their original shape on heating E.g. Spectacle frames Self-repairing car bodies Coffee-pot thermostats Stents for veins
What are hydrogels?
Can absorb/release many times their own volume in water
E.g.
Nappies
Soft contact lenses
