Chemistry GCSE Revision

Additional Science/Triple science 

Chemistry higher 

Chemicals of the Natural Environment. Part 1.

  • Atoms in molecules are held together by strong covalent bonds. 
  • The attractive forces between molecules are weak, so small molecules are often gases. 
  • Molecular compounds do not conduct electricity because their molecules are not charged. 
  • Living things are mainly made up of molecular compounds containing carbon, hydrogen, oxygen and nitrogen, with small amounts of other elements. 
  • Compounds made up of metals and non-metals have giant ionic structures. 
  • Ionic compounds have high melting points because of the strong attraction between the ions. 
  • Ionic compounds conduct electricity when they're molten or aqueous as the ions are free to move. 
  • Salts are ionic compounds. 
  • Silicon dioxide and diamond have giant covaelent structures with atoms held together in a regular network with strong bonds. 
  • Chemicals with giant covalent structures have high melting points and don't dissolve in water. 
  • Giant structures don't conduct electricity as there are no free electrons or ions. 
  • Much of the lithosphere is made up of giant covalent structures based on silicon, oxygen and other elements. 
  • All metal structures have a giant structure of metal atoms. 
  • The metallic bonding between the atoms is strong.
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Chemicals of the Natural Environment. Part 2.

  • Electrolysis turns ions back into atoms. 
  • At the anode, positive metal ions gain electrons and become metal atoms.
  • At the cathode, negative ions lose electrons and turn back into non-metal atoms.
  • Metals conduct electricity when solid and when molten because the bonding electrons can move.
  • The oxidising agent helps oxidise something else (becomes reduced). 
  • The reducing agent gains oxygen, taking it away from something else (becomes oxidised). 
  • Actual yield: the mass of the required chemical obtained after separtaing and purifying the product of the chemical reaction.
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Chemical Patterns.

  • Atoms have a central nucleus surrounded by negative electrons. 
  • Chemistry of an element is largely determined by the no. and arranegment of it's electrons.
  • No. of electrons is equal to the proton no. of the atom. 
  • Elements in the periodic table are arranged in order of their proton no. 
  • Elements in a group have similar characteristics because they have the same no. of electrons in the outer shell. 
  • When metals react with non-metals, the metal atoms lose electrons while the non-metal atoms gain electrons. This produces ionic compounds.
  • The properties of an ionic compound behave differently from the atoms of molecules in the elements.
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Chemical Synthesis.

  • Chemical synthesis provides useful products such as food additives, fertilizers, dyestuffs, paints, pigments and pharmaceuticals.
  • Acids react in characteristic ways with metals, metal oxides and metal carbonates. 
  • Alkalis neutralise acids to form salts. 
  • All acids have similar properties because they produce hydrogen ions in water. 
  • During a neutralisation reaction, hydrogen ions from an acid reacted with hydroxide ions from an alkali to make water. 
  • Chemists follow the rate of change by measuring the disappearance of a reactant or the info of a product. 
  • Factors which affect rate of change: particle size of solid reactants, the temperature and the presence of a catalyst. 
  • The collision theory: reactions occur as molecules collide. 
  • For the collisions to cause a reaction they must have enough activation energy. 
  • Titration is the method used to test a substances purity. 
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Definitions. Part 1.

  • Alkali: a compound that dissolves in water to give a solution with a pH higher than 7. 
  • Neutralisation: an alkali can be neutralised by an alkali to form a salt. 
  • Biosphere: all life on earth
  • Lithosphere: the earth's crust 
  • Atmosphere: gases
  • Hydrosphere: water
  • Catalyst: speed up reactions 
  • Combustion: when a chemical rapidly reacts with oxygen, releasing energy
  • Covalent Bonding: strong attractive forces that hold atoms together in molecules, they form between non-metallic elements
  • Electrostatic attraction: the force of attraction between between objects with opposite charges
  • Electron configuration: the number + arrangement of electrons.
  • Energy level: electrons in an atom have different energy levels and are arranged to show this.
  • Halogens: the group 7 elements.
  • Ionic bonding: the force holding together ions in an ionic compounds.
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Definitions. Part 2.

  • Metallic bondingstrong attractive forces that hold metal atoms together in a solid metal. They lose their outer electrons to form ions (+). Electrons drift freely around the lattice of positive metal ions and hold the ions together. 
  • Percentage yield: actual yield/theoretical yield
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