- Created by: CosmicPower
- Created on: 27-12-18 18:27
Atoms, Molecules and Ions
AN ATOM is the smallest particle of an element. They cannot be split into smaller particles in chemical reactions. Iron is made of iron atoms (Fe). Sulphur is made of sulphur atoms (S). Things related to atoms:
AN ELEMENT is a particular type of atom.
A COMPOUND is a substance that is created when two or more elements are chemically bonded together.
A MIXTURE is a substance made by combining two or more different materials in such a way that no chemical reaction occurs. A mixture can usually be separated back into its original components.
A MOLECULE is a small group of atoms joined together. The atoms may be the same (e.g. O2) or different (e.g. H2O). The chemical formula shows the number and type of atoms present. Non-metal compounds are made of molecules: Carbon dioxide contains CO2 molecules Methane (natural gas) contains CH4 molecules
AN ION is an atom or group of atoms with an electrical charge (+ or -). Metal compounds such as sodium chloride or copper sulphate contain ions. Sodium chloride is made of Na + and Cl - ions Copper Sulphate is made of Cu 2+ and SO4 2- ions Note that metals form positive ions while non-metals form negative ions.
Atoms are made up of smaller particles called protons, neutrons and electrons. The protons and neutrons cluster together in a small nucleus at the centre of the atom while the electrons orbit the nucleus.
The main properties of the particles are:
Particle Charge Mass Location
Electron -1 0.00055 Shells
Neutron 0 1 Nucleus
Proton +1 1 Nucleus
Every element has an atomic number, which is the number of protons in the nucleus.
Atoms are neutral so that the number of electrons is the same as the number of protons. The mass of an atom is almost entirely made up of protons and neutrons, which have the same mass as each other (the mass of electrons can be ignored). These relations can be summarised as:
ATOMIC NUMBER = NUMBER OF PROTONS NUMBER OF PROTONS = NUMBER OF ELECTRONS MASS OF ATOM = PROTONS + NEUTRONS
The electrons orbit the nucleus in 'shells'. These can hold the following numbers of electrons:
- -the innermost shell can contain up to 2 electrons
- the next shell can contain up to 8 electrons
- the next shell can contain up to 8 electrons (although this can be expanded up to 18 with some elements)
- Fluorine has atomic number 9. Its electronic structure is 2.7
- Sodium has atomic number 11. Its electronic structure is 2.8.1
- Calcium has atomic number 20. Its electronic structure is 126.96.36.199
Useful Formulae that WOULD help you:
Carbon Dioxide - CO2
Water - H2O
Oxygen gas - O2
Hydrogen gas - H2
Nitrogen gas - N2
Ammonia - NH3
Hydrochloric acid - HCl
Sulphuric Acid - H2SO4
Nitric Acid - HNO3
Filtration is a method for separating an insoluble solid from a liquid. When a mixture of sand and water is filtered:
- the sand stays behind in the filter paper (it becomes the residue)
- the water passes through the filter paper (it becomes the filtrate)
Evaporation is used to separate a soluble solid from a liquid. For example, copper sulfate is soluble in water – its crystals dissolve in water to form copper sulfate solution. During evaporation, the water evaporates away leaving solid copper sulfate crystals behind.
Simple distillation is a method for separating the solvent from a solution. For example, water can be separated from salt solution by simple distillation. This method works because water has a much lower boiling point than salt. When the solution is heated, the water evaporates. It is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.
Fractional distillation is a method for separating a liquid from a mixture of two or more liquids. For example, liquid ethanol can be separated from a mixture of ethanol and water by fractional distillation. This method works because the liquids in the mixture have different boiling points. When the mixture is heated, one liquid evaporates before the other.
The idea behind distillation is that every pure substance has its own particular melting point and boiling point, making them easier to separate by just heating up the solution. One way to check the purity of the separated liquid is to measure its boiling point. For example, pure water boils at 100°C. If it contains any dissolved solids, its boiling point will be higher than this.
Paper chromatography is a method for separating dissolved substances from one another. It is often used when the dissolved substances are coloured, such as inks, food colourings and plant dyes. It works because some of the coloured substances dissolve in the solvent used better than others, so they travel further up the paper.
Info from: https://www.bbc.com/bitesize/guides/zgvc4wx/revision/1
History of the Atom - Timeline + Info
John Dalton: Billiard Ball, 1803 - He thought that all matter was made of tiny particles called atoms, which he imagined as tiny spheres that could not be divided.
JJ Thompson: Plum Pudding Model, 1904 - Thomson carried out experiments and discovered the electron. In this model, the atom is a ball of positive charge with negative electrons embedded in it - like currants in a Christmas pudding.
Ernest Rutherford: Nuclear Model - 1911 - He designed an experiment to test the plum pudding model. In the experiment, positively charged alpha particles were fired at thin gold foil. Most alpha particles went straight through the foil. But a few were scattered in different directions. This evidence led Rutherford to suggest a new model for the atom, called the nuclear model. In the nuclear model:
- the mass of an atom is concentrated at its centre, the nucleus
- the nucleus is positively charged
Niels Bohr: Planetary(Bohr) Model - 1914 - Niels Bohr adapted Ernest Rutherford's nuclear model. Bohr did calculations that led him to suggest that electrons orbit the nucleus in shells. The shells are at certain distances from the nucleus. The calculations agreed with observations from experiments. Further experiments led to the idea that the nucleus contained small particles, called protons. Each proton has a small amount of positive charge.
James Chadwick: Current (GCSE) Model - 1932 - evidence for the existence of particles in the nucleus with mass but no charge. These particles are called neutrons. This led to another development of the atomic model, which is still used today.
Group 1: Alkali Metals - SUMMARY
- Very reactive, 1 electron on outer
- Stored in oil to stop reacting with oxygen
- Low density, soft
- Shiny, dull when reacting with oxygen as oxide layer forms
- Low bp+mp
- Form +ions by reacting with non-metals
- Fizz in H2O, h forms, metal hydroxide forms, colourless solution forms
- Produce white solids, metal chlorides
Group 7: Halogens - SUMMARY
- Poisonous non-metals
- Low bp+mp
- Coloured vapours
- Poor conductor of heat and electricity
- Test with litmus paper, bleach=chlorine
- Diatomic molecules, 2 atoms, 1 covalent bond
- 7 electrons on outer, need 1, can covalent or ionic
- Down group, reactivity decreases, inner electrons shield from the nucleus
- Form –ions by reacting with metals
- Halo+non metal=covalent
- More reactive halo displaces less reactive
- Chlorine+sodium bromide = sodium chloride + bromide as chlorine is more reactive than bromine
Transition Metals - SUMMARY
- Atoms in giant structure, metallic bonds, delocalised elctrons in sea
- Good conductor of h and e
- Hard, tough, strong, malleable
- High mp
- Form colour compounds and used as catalysts because inbetween shell 2+3, ie shell 2.5
- Less reactive than alkali metals (g1)
- Corrode slowly, react with oxygen and water slowly
- Good for mixing + making alloys, copper+zinc=brass
- Compund colour depends on ion
- Fe2+ = iron(ii)=green compound
- Fe3+ = iron (iii)=rusty brown compound