Atoms, Molecules and Compounds
Atoms can form bonds to make molecules or compounds. It's the electrons that are involved in making bonds. Sometimes an atom loses or gains one or more electrons and this gives it a charge.
(Positive if it loses an electron and negative it gains one)
If a positive ion meets a negative ion they'll be attracted and join together to form an ionic bond.
The other main type of bond is covalent bond. Atoms in a covalent bond shair a pair of electrons.
Molecular formula shows the number and type of atoms in a molecule
Displayed formula shows the atoms and the covalent bonds in a molecule as a picture.
Chemical changes are shown using chemical equations.
e.g. methane + oxygen=carbon dioxide + water
1) Find an element that doesn't balance and pencil in a number to try and sort it out
2) See where it gets you. It may create another imbalance, but if so, pencil in another numver and see where it gets you
3) Carry on chasing unbalanced elements and it'll sort itself out pretty quickly.
Emulsifiers and chemical change
- Food colour
- Flavour enhancers
Hydrophilic is end of each emulsifier molecule bonds to water molecules
Hydrophobic end of each emulsifier molecule bonds to oil molecules.
Food needs to be cooked: better taste, easier to digest, can be poisonous when raw and have little microbes.
Thermal decomposition of sodium hydrogencarbonate
Sodium hydrogencarbonate= sodium carbonate + carbon dioxide + water
Esters are often used for perfumes.
Acid +Alcohol=Ester + Water
You can make ester by heating carboxylic acid with an alcohol.
Perfumes need certain properties:
1) Easily evaporates
3) Doesn't react with water
4) Doesn't irritate the skin
5) Insoluble in water
States of matter depend on the forces between particles.
Solid particles don't move from their positions, so all solids keep a definite shape and volume
Liquids don't keep a definite shape and will flow to to fill the bottom of a container. But they do keep the same volume.
Gases don't keep a definite shape or volume and will always fill any container. When particles bounce off the walls of a container they exert pressure on walls.
How we smell stuff-volatility is the key.
The particles in a liquid perfumes only have a very weak attraction between them.
A solution is a mixture of solvent and solute.
Solute is the substance being dissolved
Solvent is liquid its dissolving into
Soluable means it will dissolve
Insoluble means it will not dissolve
Solubility measure of how much will dissolve
The solubility of a substance depends on the solvent used.
Pigments gives paints their colours.
Emulsion paints are water based. The solvent used in these paints is water, and the binding medium is usually an acrylic or vinyl acetate polymer
Traditional gloss paint and artists' oil paints are oil-based. This time, the binding material is oil and the solvent is an organic compound that'll dissolve oil.
Thermochromic pigments change when they are heated.
e.g. Baby ducks or baby spoons
Phosphorescent pigment is when it glows in the dark.
e.g. radioactive paints
Polymers are formed when lots of small molecules called monomers join together. Addition polymers are made from unsaturated monomers.
Lots of unsaturated monomer molecules can open up their double bonds and join together to form polymer chains. This is called addition polymerisation.
Strong covalent bonds hold the atoms toegther in polymer chains. Polymer poperties decide what they're used for. Light, stretchable polymers such as low density polyethene are used for plastic bags.
Hydrocarbons only cntain hydrogen and carbon atoms. All the atoms in hydrocarbon molecules are held together by covalent bonds.
Each covalent bond procides one extra shared electron for each atom. So carbon atoms always want to make a total of 4 bonds, while hydrogen atoms only want to make 1.
Alkanes are C-C single bonds.
They are saturated compounds.
Alkenes are C=C double bonds.
They are unsaturated compounds.
Crude oil is sepearted into different hydrocarbin fractions.
It is formed from the buried remains of plants and animals -its a fossil fuel.
It is a mixture of lots of different hydrocarbons.
They are seperated by fractional distillation.
You end up with the crude oil mixture seperated out into different fractions. Each fraction contains a mixture of hydrcarbons with similar boiling points
There are two types of bonds in crude oil:
1) The strong covalent bonds between the carbons and hydrogens within each hydrocarbon molecule.
2) The intermolecular forces of attraction between different hydrcarbon molecules in the mixture.
Cracking is splitting up long-chain hydrocarbons. Cracking turns long alkane molecules into smaller alkane and alkene molecules. This is a form of thermal decomposition.
When one substance breaks down into at least two new ones when you heat it.
This means breaking strong covalent bonds, so you need lots of heat and a catalyst.
Cracking produces lots of alkene molecules,which can be used to make polymers.
Long-chain hydrocarbon molecule = shorter alkane molecule + alkene
hydrocarbon + oxygen = carbon dioxide + water
hydrocarbon + oxygen = carbon dioxide + water + carbon monoxide + carbon.
When choosing best fuel:
- Energy value