OCR GCSE Chemistry

How are particles in a solid arranged?

They do not move from their positions as they all keep a definite shape and volume (in a fixed position)

What structure do particles in a solid have?

There are strong forces of attraction between particles in a very regular lattice arrangement.

How are the particles in a liquid arranged?

They are constantly moving with random motion but they tend to stick together and they do not keep a definite shape but they keep the same volume.

What are the forces of attraction like in a liquid?

There is some force of attraction between the particles but they're free to move past and alongside each other.

How does a high temperature effect particles in a liquid?

The hotter the liquid gets, the faster they move- causing the liquid to expand. If the liquid becomes too hot, it will evaporate and become a gas.

How does a low temperature effect particles in a liquid?

If the temperature gets too cold, the liquid will freeze and become a solid.

How are the particles in a gas arranged?

They do not have a definite shape or volume. They are free to move and they have a lot of kinetic energy. When they bounce off the walls of a container, the exert a pressure on the walls.

What are the forces of attraction like in a gas?

There's next to no force of attraction between the particles as they are free to move anywhere. They travel in straight lines and only interact when they collide.

How does a high temperature effect particles in a solid?

The hotter the solid becomes, the more the particles vibrate- causing solids to expand slightly when heated. Eventually they will melt and become a liquid.

How does a high temperature effect particles in a gas?

The hotter the gas gets, the faster they move and they will either expand or their pressure will increase when heated.

How does a low temperature effect particles in a gas?

If the temperature gets too cold, the gas condenses and becomes a liquid.

What is an advantage of the particle theory?

It is a great model for explaining the three states of matter.

What is a disadvantage of the particle theory?

The model does not show any of the forces between the particles so there is no way of knowing how strong the forces are.

What is a physical change?

A physical change is when a substance changes from one state of matter to another.

What is a chemical change?

A chemical change is when bonds between atoms break and the atoms change places. The atoms in the substance you start with re-arrange themselves to form different chemicals. They are often hard to reverse.

Who, in the 19th century, described atoms as 'solid spheres'?

John Dalton describes atoms as solid spheres and said that different spheres made up the different elements.

Who concluded that atoms were not solid spheres in 1897?

JJ Thomson. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles (electrons).

What did JJ Thomson name his new theory that proved the 'solid sphere' theory wrong?

The Plum Pudding Model

Who conducted the gold foil experiment in 1909?

Ernest Rutherford and his students: Hans Geiger and Ernest Marsden

What was the gold foil experiment?

Ernest Rutherford and his students fired positively charged alpha particles at an extremely thin sheet of gold.

What happened to the alpha particles when they were fired at the sheet of gold?

Most of the particles went straight through the gold sheet, but some were deflected more than expected, and a small number were deflected backwards.

What did Rutherford name his theory that proved the plum pudding model wrong?

The Nuclear Atom Theory.

What is the nuclear atom theory?

That there is a tiny positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons and that the atom was mostly empty space.

What was the Plum Pudding Model?

The Plum Pudding Model showed that atoms must contain even smaller, negatively charged particles (electrons).

What did Niels Bohr propose?

Bohr suggested that electrons can only exist in fixed orbits (shells) and not anywhere in between and each shell has a fixed energy.

What supported Bohr's theory?

Bohr's theory was supported by many experiments and it helped to explain other scientists' observations at the time. It is pretty close to the current version of the atom.

What is the relative mass of a proton?

1.

What is the relative charge of a proton?

+1.

What is the relative mass of a neutron?

1.

What is the relative charge of a neutron?

0.

What is the relative mass of an electron?

0.0005 (almost 0).

What is the relative charge of an electron?

-1.

Where is the nucleus found in an atom?

It is located in the middle of the atom.

What does the nucleus contain?

Protons and Neutrons.

What charge does the nucleus have?

A positive charge because of the protons.

What is the whole mass of an atom?

What is the size of a nucleus' radius?

Where are electrons found in the atom?

Electrons orbit around the nucleus in shells.

What is the size of an electron's radius?

How are molecules formed?

Molecules are doomed when atoms bond together. Molecules can be made of the same element and different elements.

How big is a nanoparticle?

They are typically made of around 100 atoms and range from 1nm to 100nm in size.

What is the mass number and where is it on the periodic table?

The mass number is the total number of protons and neutrons and it is found under the element's symbol (it is usually the larger number).

What is the atomic number and where is it on the periodic table?

The atomic number is the number of protons and it is found above the element's symbol.

How can you find the number of neutrons?

You can find the number of neutrons by subtracting the atomic number from the mass number .

Why do neutral atoms have no charge overall?

Neutral atoms have no charge overall because they have the same number of protons and electrons. The number of electrons in a neutral atom is also equal to it's atomic number.

How are ions formed?

Ions are formed when atoms (or groups of atoms) gain or lose electrons.

When are negative ions formed?

Negative ions are formed when atoms gain electrons and they have more electrons than protons.

When are positive ions formed?

Positive ions are formed when atoms lose electrons and they have more protons than electrons.

What are isotopes?

Isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons.

How many protons, neutrons and electrons does carbon-12 have?

Protons=6
Neutrons=6
Electrons-6

How many protons, neutrons and electrons does carbon-13 have?

Protons=6
Neutrons=7
Electrons=6

What are natural materials?

Chemicals, or mixtures of chemicals that come from living things (cotton & paper- plants, silk & wool- animals).

What are synthetic materials?

Chemicals, or mixtures of chemicals, which have been produced by chemical synthesis.

What is crude oil made of?

Hydrocarbons- compounds made entirely of hydrogen and carbon atoms. Their properties change as the chain get longer. There are strong covalent bonds between the carbons and hydrogens within each hydrocarbon molecule. There are intermolecular forces of attraction between different hydrocarbon molecules. Only a small percent of it is used for chemical synthesis the rest if used for fuel.

Describe in terms of intermolecular forces and bonds how crude oil needs different boiling points to break it up.

When crude oil is heated the molecules are supplied with extra energy; thus the molecules moves about more. Eventually, a molecule may have enough energy to overcome the intermolecular forces that keep it with the other molecules. The covalent bonds are much stronger meaning you don't end up with small molecules. The intermolecular forces are easier to break in smaller molecules in comparison to larger ones. Meaning more energy is needed to break larger hydrocarbons out of crude oil.

Describe in terms of forces and energy need to break bonds is determined by the size of the molecule.

Smaller molecules have weaker intermolecular forces between them meaning that less energy is needed to break their bonds in order to form a gas. Larger molecules have stronger intermolecular forces since the size of the force increases as the size of the molecule increases; this means that more energy is needed to break their bonds.

What are the uses of crude oil?

It is used for fuels, to make plastics such as polyethylene, small amounts of hydrocarbons are used to make new compounds for use in thinks such as plastics, medicines, fertilisers and even food.

How is crude oil separated?

Into fractions by fractional distillation depending on the chain length. Smaller molecules have a lower boiling point, very volatile, flow easily and are easy to ignite. *Vis Versa*

What happens in fractional distillation?

The crude oil is heated at 400°C for the hydrocarbons to be evaporated, this passes into a fractional distillation column at the bottom. The vapour moves up the FD column and cools. Its hotter and the bottom and cooler at the top. Each fraction condenses when it has cooled below its boiling point (the larger hydrocarbon molecules with a high boiling point condense lower down the column, and the smaller molecules with a low boiling point condense higher up). Other gases will leave at the top of the tower. The fractions can then be used as fuels, lubricants and the raw materials for chemical synthesis

What holds molecules in a liquid or solid together?

Intermolecular forces. In hydrocarbons, longer molecules have stronger forces. These need more energy to be broken, so the boiling point is higher.

What are the properties and uses of polythene?

It has a low density, so is light, and is flexible and easily moulded. It can be used for plastic bags and containers.

What are the properties and uses of polystyrene?

It has a low density, so is light, and it is stiff and water resistant. It is also a thermal insulator. It can be used for coffee cups, meat trays, egg cartons and in the protection of appliances.

What are the properties and uses of nylon?

It has a low density, so is light, and it is tough and waterproof. It also blocks UV light. It can be used for clothing and climbing ropes.

What are the properties and uses of polyester?

It has a low density, so is light, and is tough and waterproof. It can be used for clothing and bottles.

What is polymerisation?

The chemical process during which hydrocarbon monomers are joined to make longer strings of molecules (polymers).

How can polymerisation be used?

Polymers have different physical properties depending on how their molecules are arranged and held together, meaning they have different uses. For example, Carrier bags (strong and waterproof), window frames (unreactive and doesn't rot), non-stick frying pans. Heat-resistant polymers such as melamine resin and polypropene are used to make plastic kettles.

Why have polymers replaced natural materials for some uses?

They have more benefits in comparison to the traditional materials. For example, synthetic fibers like nylon are used to replace fabrics as they are lighter, more durable, water- resistant and cheaper. The main down-side is that they aren't breathable making them uncomfortable.

What happens if polymer chains are packed close together or spread out?

If the polymer chains are packed close together, it will have a high density.
If a polymer chains are spread out the material will have a low density

What happens if the polymer chains are held together by weak forces?

If polymer chains are held together by weak forces then they are free to slide over each other. The bonds holding the atoms together are strong but the forces between molecules are weak. This means that the material (plastic) can be stretched easily (is flexible),will have a low melting point won't be stiff, won't be hard.

What happens if the polymer chains are held together by strong forces?

If a polymer chain is held together by strong forces then they have high melting points and can't easily be stretched as the crosslinks hold the chains firmly together. Crosslinks are chemical bonds between the polymer chains and hold them in a regular structure. It means it will be very strong, stiff hard and have a high melting point.

Why is rigid PVC used in windows?

It is weather-resistant, strong, and durable; making window frames more secure. And do not need constant painting.

What is natural rubber?

A mass of long-chain molecules, where the molecules are held together by very weak intermolecular forces. This makes it flexible and gives it a low melting point (less energy is needed to separate the molecules).

What is vulcanised rubber?

A mass of tangled molecules, held together by cross-links, giving it strong covalent bonds between the molecules. This makes it more rigid, and gives it a high melting point (more energy is needed to separate the molecules). It is used for conveyor belts and car tyres.

How does chain length affect affect a polymer?

Depending on the length shorter chains will have weaker forces of attraction between molecules (compared to long chains) so the polymer chains can easily slide past each other, making the material flexible.
It will also have weak forces of attraction, it requires less energy to separate the molecules out of the solid structure and into a liquid formation, therefore it will have a low(er) melting point than a long chained polymer

*Vis Versa*.

What is the effect of increasing or decreasing the chain length?

Making a polymer chain longer will mean it will be less flexible, a higher melting point, stiffer and stronger.
Making a polymer chain shorter will mean it will be flexible, low melting point, less stiff and weaker.

What is the effect of cross-links?

These agents chemically bond the polymer chains linking them together.
These cross-links between the molecules mean that the molecules are locked in a regular arrangement which stops the chains from uncoiling and slipping over each other. The result of this is that is makes the rubber less flexible, stronger , stiffer and harder.
It also gives the rubber a high melting point because more energy is needed for the molecules to separate and break out of the solid thus more heat resistant.
.

What is vulcanisation?

A type of cross-linking, where sulphur atoms join rubber molecules. This creates vulcanised rubber.

What is the effect of adding plasticisers?

Plasticisers are usually an oily liquid with small molecules which can be added to polymers during their manufacture.
The small molecules sit between the polymer chains, they push the polymer chains further apart, which weakens the forces between them.
This means that less energy is needed to separate them and they slide over each other more easily.

What is the effect of making a polymer crystalline?

In a crystalline polymer, the molecules are lined up in a regular way (in neat lines) as in a crystal.
It has straight chains with no branches so that the chains can fit close together.
This means that the forces between the molecules are slightly stronger and more energy is needed to separate them so it has a higher melting point.
As more chains are packed in, it has a higher density, and is stronger.
The branches stop the molecules from packing neatly.

What is nanotechnology?

The use and control of structures that vary on a nanoscale- 1-100 nanometers (1 millionth of a millimeter). These occur naturally in sea spray, for example, but most nanoparticles are created by scientists for nanotechnology purposes. It can also be created by accident for example as the smallest particulates from combustion of fuels.

How is nanotechnology used?

Nanoparticles can modify the properties of polymers. For example, some are used in clothes for antibacterial purposes (which prevents bad smells), and some are used in certain sports equipment (tennis rackets, golf clubs etc.) to make them lighter but stronger.

What do nanoparticles show in comparison to larger particles?

Different properties this is because they have a much larger surface area of the nanoparticles compared to their volume.

What are the dangers of Nanoparticles?

The way they affect the body isn't fully understood, new products need to be tested thoroughly to minimize the risks.
The long-term impacts are not fully known. Many people want products containing nano technology to be clearly labeled.
Some are worried that products containing nanoparticles have been made available before the effects on human health have been properly investigated. We don't know the long term imapacts.

Exothermic

Gives out energy. Usually in the form of heat, is shown with a rise in temperature.

Exothermic Example

Burning Fuels.

Endothermic

Takes in energy. Usually in the form of heat, is shown with a fall in temperature.

Endothermic Example

Thermal Decomposition.

Bond Breaking

Requires energy, so is Endothermic. Energy required to break bonds is greater than energy used in breaking old bonds.

Bond Making

Energy is released when formed, is Exothermic. Energy released is greater than energy used in breaking old bonds.

Specific Heat Capacity (SHC)

Amount of energy required to raise the temperature of 1 gram of a substance by 1 celcius.

Calorimetric

An experiment involving heating water by burning liquid fuel.

Energy given out per gram

Energy Released / Mass of Fuel Burnt.

Example of a Slow Reaction

Rusting

Example of a Fast Reaction

Explosion

How could you measure gas production?

Change in mass, or Gas Syringe.

Reaction Rate

The speed of reatants being turned into products.

Collision Frequency

How often particles collide during a reaction. More collisions - Higher reaction rate.

Energy Transfer during Collision

Particles need enough energy for a collision to be successful.

Yield

The amount of product you get from a reactant.

Limiting Reactant

The reactant which runs out first, stopping the reaction.