- Created by: mbrewer03
- Created on: 21-01-19 21:03
- All substances are made up of atoms.
- The periodic table lists all the chemical elements, with eight main groups each containing elements with similar chemical properties.
- Elements contain only one type of atom.
- Compounds contain more than only one type of atom.
- An atom has a tiny nucleus at its centre, surrounded by electrons.
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C1.2 Chemical equations
- No new atoms are ever created or destroyed in a chemical reaction: the total mass of reactants = the total mass of products.
- There is the same number of each type of atom on each side of a balanced symbol equation.
- You can include state symbols to give extra information in balanced symbol equations. These are (s) for solids, (I) for liquids, (g) for gases, and (aq) for aqueous solutions.
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C1.3 Separating mixtures
- A mixture is made up of two or more substances that are not chemically combined together.
- Mixtures can be separated by physical means, such as filtration, crystallisation, and simple distillation.
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Fractional distillation and paper chromatography
C1.4 Fractional distillation and paper chromatography.
- Fractional distillation is an effective way of separating miscible liquids, using a fractionating column. The separation is possible because of the different boiling points of the liquids in the mixture.
- Paper chromatography separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper. The different substance are separated because of their different solubilities in the solvent used.
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History of the atom
C1.5 History of the atom
- The ideas about atoms have changed over time.
- New evidence has been gathered from the experiments of scientists who have used their model of the atom to explain their observations and calculations.
- Key ideas were proposed successively by Dalton, Thomson, Rutherford, and Bohr, before arriving at the model of the atom you use at GCSE level today.
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Structure of the atom
C1.6 Structure of the atom
- Atoms are made of protons, neutrons and electrons.
- Protons have a relative charge of +1, and electrons have a relative charge of -1. Neutrons have no electric charge. They are neutral.
- The relative masses of a proton and a neutron are both 1.
- Atoms contain an equal number of protons and electrons, so carry no overall charge.
- Atomic number = number of protons (= number of electrons).
- Mass number = number of protons + neutrons
- Atoms of the same element have the same number of protons (and hence electrons) in their atoms.
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Ions, atoms, and isotopes
C1.7 Ions, atoms, and isotopes
- Atoms that gain electrons form negative ions. If atoms lose electrons they form positive ions.
- You can represent the atomic number and mass number of an atom using the notation Mg, where magnesium's atomic number is 12 and it's mass number is 24.
- Isotopes are atoms of the same element with different numbers of neutrons. They have identical chemical properties, but their physical properties, such as density, can differ.
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C1.8 Electronic structures
- The electrons in an atom are arranged in energy levels or shells.
- The lowest energy level (1st shell) can hold up to 2 electrons and the next energy level (2nd shell) can hold up 8 electrons.
- The 4th shell starts to fill after 8 electrons occupy the 3rd shell.
- The number of electrons in the outermost shell of an element's atoms determines the way in which that element reacts.
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