C3: Structure and Bonding Flashcards
What are the 3 states of matter?
Solids
Liquids
Gases
What is all matter made up of?
Particles
What is particle theory and how are particles represented?
Particle theory describes the movement and arrangement of particles in different states of matter (solids, liquids, gases)
Particles are represented as small solid spheres
Describe the particle theory representation in solids?
Arrangement: Particles in a solid are packed closely together in a fixed arrangement
Movement: They vibrate constanty
Describe the particle theory representation of liquids?
Arrangement: Particles in a liquid are close together in a changing, random arrangement
Movement: They can move around
Describe the particle theory representation of gases?
Arrangement: Particles in a gas are much further apart in a random arrangement
Movement: They move around very quickly
What happens to the particles when a solid becomes a liquid?
As the temperature increases, the particles in a solid vibrate faster
At the melting point enough energy is transferred to break the forces between the particles
The particles then break away from their fixed position and start to move around and a liquid is formed
When does a solid become a liquid?
At its melting point
What happens to the particles when a liquid becomes a gas?
As the temperature increases, the particles in a liquid vibrate faster
As more energy is transferred to the substance some of its particles can escape the liquid before boiling point is reached - this means the liquid is evaporating
At the boiling point, bubbles of gas form within the liquid and rise up to the surface and a gas is formed
What can you say about the forces between particles in substances with higher / lower boiling and melting points
Substances with higher boiling and melting points = stronger forces between their particles
Substances with lower boiling and melting points = weaker forces between their particles
What are the limitations of the particle model of solids, liquids and gases?
The particle model assumes that particles are solid with no forces between them
However the limitations are:
-> Particles can be atoms, molecules or ions
-> Can contain many atoms
-> Vary in size
-> Aren’t solid or spherical
When are compounds formed?
Compounds are formed when 2 or more elements react together
How do atoms of elements join together?
By sharing electrons or by transferring electrons to achieve stable electronic structures
Which atoms already have stable electronic structures?
Noble gases - group 0 elements
What is covalent bonding?
When non-metallic elements join together by sharing electrons
What is produced when metallic elements react with non-metallic compounds?
When metals react with non-metals they form ionic bonds
What happens in ionic bonding?
The metallic atoms lose electrons and form positive ions (cation)
The non-metallic atoms gain electrons and form negative ions (anions)
The ions have a full outer shell of electrons - the same as noble gases
The two oppositely charged ions attract each other in the compound - this is ionic bonding
What happens to group 1 elements in ionic bonding?
Group 1 elements are metals - they have 1 electron in their highest energy level (outer shell) which they lose to the non-metal
They form +1 charged ions
These react with Group 7 elements (non-metals) that form -1 charged ions
What happens to group 2 elements in ionic bonding?
Group 2 elements are metals - they have 2 electron in their highest energy level (outer shell) which they lose to the non-metal
They form +2 charged ions
These react with Group 6 elements (non-metals) that form -2 charged ions
What can be used to show the electrons in the outer shell of an atom and draw this reaction for Na + Cl -> NaCl
Dot and cross diagrams
Draw NaCl reaction as a dot and cross and check the answer
When are ionic compounds formed?
When metals react with non-metals
What holds ionic bonds together?
Ionic bonds are held together by strong forces of attraction between oppositely charged ions
These ionic bonds can come together to form a giant structure also known as a giant lattice
What is a giant lattice / structure?
A huge 3D network of atoms / ions as seen in ionic bonding
Why are ionic compounds usually solid at room temperature?
There are strong electrostatic forces of attraction between the oppositely charged ions
These require lots of energy to overcome and break these bonds hence they have HIGH boiling and melting points
Why can ionic compounds conduct electricity when molten or dissolved in water?
When the ionic compound is molten / dissolved in water the ions can freely move
This allows them to carry charge through the liquid and conduct electricity
What do non-metals need to do in order to achieve stable electronic structures?
How can they do this?
Non-metals need to gain electrons to achieve stable electronic structure (full outer shell)
They can do this by sharing electrons with other atoms
What are molecules?
These are substances that have atoms held together by covalent bonds
What can you also sometimes see in covalently bonded molecules and what is an example of this?
You can also see double (or triple) covalent bonds eg O2
What are the different structures you can see with covalently bonded substances?
Covalently bonded substances can either be simple molecules
Or have multiple covalent bonds and form giant covalent structures
What is a giant covalent structure?
A huge 3D network of covalently bonded atoms
How are the boiling and melting points of substances with simple molecules?
Substances made of simple covalent bonds have low melting and boiling points
Why do substances with simple molecules have low boiling and melting points?
They have low melting / boiling points because although there are strong covalent bonds in between the atoms
There are weak intermolecular forces holding in between the simple molecules that require little energy to be broken apart
What happens when a substance made of simple covalent bonds melts / boils?
When a substance made of simple covalent bonds melt / boils
The weak intermolecular forces in between simple molecules are broken however the strong covalent bonds in between atoms are not broken
What are intermolecular forces?
This is the attraction between individual molecules in a covalently bonded substance
When can the intermolecular forces between covalently bonded simple molecules be stronger? What does this mean?
The larger the simple molecule, the stronger the intermolecular forces
This means larger simple covalent substances have higher boiling and melting boiling points when compared to smaller molecules
What are polymers?
Polymers are very large molecules made up of many small molecules covalently bonded together
Give an example of a polymer and what it is made of?
Poly(ethene) is a polymer made up of thousands of ethene (C2H4) molecules
What do polymers look like at room temperature and why?
Polymers are solids at room temperature
This is because they are very large molecules which means they have stronger intermolecular forces between them that need more energy to be broken
Why do simple covalent molecules not conduct electricity?
They do not conduct electricity because unlike ions there is no overall charge on the simple molecules
What is an example of a substance that forms a giant covalent structure?
Diamond - there is a huge network of atoms that have strong covalent bonds in between them
This is why diamonds are very hard
What are the features of substances that form giant covalent structures?
They have high melting and boiling points as there are only strong covalent bonds and no intermolecular forces
These strong covalent bonds require a lot more energy to be broken apart
What are the limitations in using models to represent molecules?
The models do not show the actual shape of the molecule
The dot and cross method shows electrons from different atoms differently even though they all look the same
Electrons are shown in fixed positions but they are constantly moving
In giant structures the models only show a small fraction of the atoms / ions present
Describe the structure of diamond
Diamond is a form of carbon that forms a giant covalent structure
Each carbon atom in diamond is covalently bonded to 4 other carbon atoms
This makes diamond very hard and have a very high melting point
Does diamond conduct electricity?
No
What are some other substances that form giant covalent structures?
Graphite
Silicon
What is graphite used for?
Graphite is used in pencils (the grey part that rubs onto paper)
Describe the structure of graphite
In graphite, each carbon atom is covalently bonded to 3 other carbon atoms
They form hexagonal rings which are arranged in giant layers
In between the layers of graphite there are no covalent bonds but instead weak intermolecular forces
This means the layers of graphite can easily slide over each other when you write using a pencil - this is why graphite is softer and slippery compared to diamond
Can graphite conduct electricity and why?
Yes it can
Since in graphite each carbon atom is bonded to 3 atoms instead of 4, there is 1 electron free and delocalised
This free delocalised electron allows graphite to conduct electricity and heat
What are 2 similarities and 2 differences between diamond and graphite
Similarites:
- They are both forms of carbon
- They both form giant covalent structures
Differences:
- In diamond, each carbon atom is bonded to 4 others, in graphite each carbon atom is bonded to 3 others and there is a delocalised electron
- Diamond has a 3D structure, Graphite has a 2D structure
- Diamonds are transparent, Graphite is grey / opaque
- Diamonds are hard, Graphite is soft / slippery
- Diamonds are poor conductors of heat / electricity whereas graphite is a good conductor of heat / electricity due to the delocalised electron
What are fullerenes?
A form of carbon where atomms join together to make large hollow shapes
A fullerene is based on hexagonal (6-sided) rings of carbon atoms - they can also have pentagonal (5-sided) and heptagonal (7-sided) rings instead
What can fullerenes be used for?
They can be used for drug delivery into the body
Lubricants
Catalysts
What are carbon nanotubes?
These are cylindrical fullerenes
What are the features of carbon nanotubes?
They are very thin cylinders with very high length to diameter ratio
They have high tensile strength - useful to reinforce materials in tennis rackets making them stronger
They have delocalised electrons - high electrical conductivity and can be used in electronics
Describe the structure of graphene
Graphene is a form of carbon which has a single layer of graphite
This means there is a layer of hexagonal rings one carbon atom thick
What are the features of graphene? Where can they be used?
Graphene is an excellent conductor of electricity
Graphene has a very low density
Graphene is very very strong for its mass
Due to these featuers graphene is very useful in electronics and composites
What are the similarities and differences between graphite and graphene
Similarities:
Both are forms of carbon that form hexagonal rings with covalent bonds between carbon atoms
Differences:
Graphene is made up of a single layer of atoms one carbon atom thick
Graphite is made up of multiple layers
What holds together the giant structure in metallic bonding?
The electrostatic forces of attraction between the positively charged ions and the sea of delocalised electrons
How are atoms arranged in metals?
Atoms in metals are closely packed together and arranged in regular layers
This is because the atoms in a metallic elemnet are the same size
What happens to electrons when metal atoms pack closely together?
When metal atoms are closely packed together, the electrons in the highest energy level (outer shell) delocalise and move freely between atoms
This leads to a LATTICE OF POSITIVELY CHARGED IONS and a SEA OF DELOCALISED ELECTRONS
What are the features of pure metals and why?
Pure metals are too soft to be used and can be easily bent and shaped
This is because the atoms in a pure metal are closely packed together in layers in a giant structure
These layers can easily slide over each other allowing the metal to be soft and easily bent / shaped
What are alloys?
A mixture of at least one metal with other elements (metal or non-metal)
How do the features of alloys differ from that of pure metals? Why?
Alloys are harder than pure metals
This is because in an alloy the different atoms from different elements have different sizes
This makes it harder for the layers of atoms to easily slide over each other and make the alloy bent / re-shaped
What is the boiling and melting points of metals like and why?
Metals have high boiling and melting points
This is because there are strong electrostatic forces of attraction between the positively charged ions and the sea of delocalised electrons
This means that lots of energy is required to break apart this bonds and disrupt the ions to make it a liquid / gas
Are metals good conductors of heat & electricity and why?
Yes - metals are good conductors of heat and electricity
This is because they have a sea of delocalised electrons which allows electrical charge and thermal energy to be quickly transferred throughout the giant metallic strucutre
