changing of state in a substance
1. when a solid is heated, its particles gain more energy.
2. this makes the particles vibrate more, which weakens the forces that hold the solid together. this makes the solid expand.
3. at a certain temperature, the particles will have enough energy to break free from their position. this is called MELTING and the solid turns into a liquid.
4.when a liquid is heated the particles gain even more energy.
5. this energy makes the particles move and vibrate faster, which weakens and breaks the bonds holding the liquid together.
6. at a certain temperature, the particles have enough energy to break their bonds. this is called EVAPOURATION and the liquid turns into a gas.
movement of particles
- diffusion is the process by which particle mix and spread, through collisions with other particles.
- it is faster in a gas than a liquid. this is because particles move faster in a gas. so they collide with more force and more frequently.
- as the temperature rises, particles take in energy and move faster. so diffusion is faser also.
comparing the rates of diffusion in gases
- particles of ammonia gas and hydrogen chloride gas diffuse rom opposite ends of the tube.(molecules)
- when they meet, they combine to form a white cloud of ammonium chloride.
- they white cloud forms closer to the right side of the tube as the ammonia molecules have diffused acros the tube faster. that is because they are lighter (the relative molecular mass is 17)
the lower its relative molecular mass, the faster a gas will diffuse.
- contains protons and neutrons
- it has a positive charge because of the protons.
- most of the atoms mass is concentrated in the nucleus.
- they move around the nucleus in energy levels called shells.
- they are negatively charged.
- they have virtually no mass.
have a neutral charge and are held in the nucleus.
the number of protons, neutrons and electrons
Number of Protons = Atomic Number
- The atomic number is the number of protons in an atom of an element.
Number of Electrons = Number of Protons = Atomic Number
- atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons.
Number of Neutrons = Mass Number - Atomic Number
elements, compounds and mixtures
Elements: elements consist of one type of atom only.
Compound: A compound is a substance formed when two or more chemical elements are chemically bonded together.
Mixture: A mixture is made from molecules of elements and compounds that are simply mixed together, without chemical bonds.
Molecule: molecules are groups of atoms from the same element that bond together by covalent bonds.
filtration and crystalisation
- chromaography works because different dyes will move up the paper at different rates.
- some dyes will stck to the paper and some will dissolve more in the solvent and more quickly.
- the distance the dyes travel up the the paper depends on the solvent and the paper used.
- helps you identify different dyes.
Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points. Distillation is commonly used to separate ethanol.
The mixture is heated in a flask. Ethanol has a lower boiling point than water so it evaporates first. The ethanol vapour is then cooled and condensed inside the condenser to form a pure liquid.
Acids and alkalis: pH scale and testing
- the stongest acid has a pH of 0.
- the strongest alkali has a pH of 14.
- a neutral substance has a pH of 7 ( e.g. pure water )
Testing: Universal indicator - shows the same colours as on the pH scale.
Litmus paper - it's red in acidic solutions, puple in neutal solutions and blue in alkaline solutions.
Phenolphthalein - will become colourless in acidic solutions and turn pink in alkaline solutions
Methyl Orange - it is red in acidic solutions and turns to yellow in alkaline solutions
Acids: pH 0-6 ( dark red to yellow )
Neutral: pH7 ( light to dark green )
Alkali: pH 8-14 ( blue to purple )
neutralisation in acids and alkalis
An ACID is a source of hydrogen ions (H+)
A BASE ( or alkali ) is a source of hydroxide ions ( OH-)
The reaction between an acid and an alkali is called neutralisation.
Acid + alkali = salt + water
the products produced are NEUTRAL, hey will have a pH of 7.
reactions of acids: metal oxides
Acids react with metal oxides :
- metal oxides are bases
- they react with acids to form a salt and water.
different types of acid:
- hydrochloric acid - the salt produced will be a metal chloride
- Sulfuric acid - the salt produced will be a metal Sulfate
- Nitric acid - the salt produced will be a metal nitrate
e.g. hydrochloric acid + copper oxide = copper chloride + water
sulfuric acid + zinc oxide = zinc sulfate + water
nitric acid + copper oxide = copper nitrate + water
reactions of acids: metal carbonates
acids react with metal carbonates:
- the reaction produces a salt, water and carbon dioxide.
- the salt produced depends on the acid used.
Acid + metal carbonate = Salt + water + carbon dioxide
e.g. hydrochloric acid + sodium carbonate = sodium chloride + water + carbon dioxide
Sulfuric acid + calcium cabonate = calcium sulfate + water + carbon dioxide
definition of an Alloy:
- a mixture of a metal with other elements
- e.g. Brass is an alloy of copper and zinc.
- the added substance in alloys can be other metals or non metals.
- they are chosen to improve certain properties of metal.
the periodic table
The group number of an element in the periodic table
is the same as the number of electrons in its ouer shell.
The period (row) in which an element is found shows the number of electron shells.
The group 1 elements are found on the left hand side of the periodic table. They are called the alkali metals because they form alkaline compounds.
reactions with group 1 elements
Reactions of group 1(alkaline metals) elements with:
- elements become more reactive down the group as the atomic number increases.
- atoms lose electrons more easily down the group as the outer electron gets further away from the nucleus which means there is less attraction between the electron and the nucleus. therefore the electron is more easily lost making it more reactive.
The group 1 metals react vigorously with oxygen to form metal oxides. Lithium burns with a red flame, sodium with a yellow-orange flame, and potassium burns with a lilac flame.
group 0 elements: noble gases
Group 0 elements are all colourless gases
1. group 0 elements are called the noble gases and include the elements helium, neon and argon.
2. they do not react very much.
3.they have a full outer shell of electrons, this means it is unlikely for them to lose or gain electrons.
Group 7: halogens
Elements in group 7 are called the halogens
1. The properties of the elements in group 7 gradually change as you go down the group - as the atomic number of the halogens increases the elements have a darker colour and a higher boiling point.
2. they are in the non metal group, so they form ions in ionic bonding.
3. the higher up group 7 an element is, the more reactive it is. this is because the shell with the missing electron is nearer to the nucleus.
4. As they have 7 electrons in their outer shell, the less distance that shell is from the nucleus the stronger the force of attraction will be to gain and extra electron for a full outer shell.
More reactive halogens will displace less reactive ones:
1. The elements in group 7 take part in displacement reactions.
2. A displacement reaction is where a more reactive element displaces a less reactive element from a compound.
3. Halogen dislacement reactions involve a transfer of electrons.
e.g. Cl2 + 2I- = 2Cl- + I2
in this reaction each of the chlorine atoms gain an electron to form 2 negative Cl ions and the 2 iodide ions form a neutral I2 molecule. this happens as chlorine is more reactive than iodine and has a stronger pull towards the nucleus as there are less electron shells.
oxidation and reduction
e.g. Na => Na + = loss of electrons - oxidation
O => O2- = gain electrons - reduction
Burning fuels can produce polllutants:
carbon monoxide is produced by incomplete combustion - it s formed when hydrocarbon fuels are burnt without enough oxygen
- carbon monoxide is poisonous - stops the blood from carrying oxygen arround the body, combining with the haemoglobin stoping the oxygen from combining with it.
Sulfur dioxide and Nitrogen oxides come from burning fuels
metals and non metals
- conduct electricity and heat
- they are mostly malleable
- tend to be shiny
- tend to have a high density and be heavy.
- usually have high melting points
- form positive ions, in reactions
- do not conduct electricity
- are usually brittle when solid - they break up when hammered
- look dull when a solid
- have a low density
- have low melting points
- they form negative ions in a reaction ( except for Hydrogen H+)
the reacivity series
Iron and steel rust when they come into contact with water and oxygen. Both water and oxygen are needed for rusting to occur. In the experiment below, the nail does not rust when air - containing oxygen - or water is not present.
Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. Here is the word equation for the reaction:
iron + water + oxygen → hydrated iron(III) oxide
The periodic table: transition metals
The elements in the centre of the periodic table, between groups 2 and 3, are called the transition metals.
The transition metals have the following properties in common:
- they form coloured compounds
- they are good conductors of heat and electricity
- they can be hammered or bent into shape easily
- they are less reactive than alkali metals such as sodium
- they have high melting points - but mercury is a liquid at room temperature
- they are usually hard and tough
- they have high densities
our atmosphere: oxygen
Experiment for oxygen in the atmosphere:
The percentage of oxygen in the air can be measured by passing a known volume of air over hot copper and measuring the decrease in volume as the oxygen reacts with it. Here are the equations for this reaction:
copper + oxygen → copper oxide
2Cu + O2 → 2CuO
Gas syringes are used to measure the volume of gas in the experiment. The starting volume of air is often 100 cm3 to make the analysis of the results easy, but it could be any convenient volume. In the simulation, there is 100 cm3 of air at the start.