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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- 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 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 bonding: strong 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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