physical and chemical changes
1) Understand the differences between Physical and Chemical changes
- Physical changes produce no new substances. The substance undergoing change may have a different shape or state but is the same substance at the end. Eg. boiling water, melting ice, breaking a bottle, crumbling paper.
- Chemical changes produce a new substance and either absorbs or releases heat during the process. Chemical changes happen on an atomic level. Eg. burning wood, dissolving salt in water, digesting food.
- Some chemical reactions can be reversed by changing the reaction conditions (Limited to the effects of heat and water on hydrated and anhydrous copper(II) sulfate and cobalt(II) chloride.
- When anhydrous copper (II) sulfate crystals are added to water they turn blue and heat is given off (exothermic); this reaction is reversible. This form of Copper (II) Sulfate in the crystals is known as Hydrated Copper (II) Sulfate because it contains water of crystallisation.
- When Copper (II) Sulfate crystals are heated in a test tube, the blue crystals turn into a white powder and a clear, colourless liquid (water) collects at the top of the test tube. When Hydrated Copper (II) Sulfate is heated, it loses its water of crystallisation and turns into anhydrous Copper (II) Sulfate:
elements, compounds and mixtures
2) Describe the differences between elements, mixtures and compounds, and between metals and non-metals
- Element: substance that cannot be split into anything simpler in a chemical reaction. Each element has a unique proton number.
- Mixture: two or more elements mixed together but not chemically combined
- Compound: substance in which two or more different elements are chemically combined
- Metals: Strong. Good conductors of heat & electricity. High m.p. and b.p.. High density. Forms basic oxides. Forms cations in reactions. Malleable and ductile. Sonorous. Some are magnetic.
- Non-metals: Brittle. Poor conductors of heat & electricity (except graphite). Lower m.p. and b.p. than metals. Low density. Forms acidic oxides. Forms anions in reactions.
3) Define the terms Solvent, Solute, Solution and Concentration
When a solid dissolves in a liquid,
- the substance that dissolves is called the solute.
- the liquid in which it dissolves is called the solvent.
- the liquid formed is a solution.
- a saturated solution is a solution into which no more solute can be dissolved.
- The concentration of a solution is a measure of the number of particles of the solute in the solvent.
atomic structure and periodic table
4) Atomic structure and the Periodic Table
Mass (Atomic mass)
- Proton number (atomic number): as the number of protons in the nucleus of an atom
- Nucleon number (mass number): as the total number of protons and neutrons in the nucleus of an atom
- Atoms of the same element which have the same proton number but a different nucleon number.
- Isotopes have the same properties because they have the same number of electrons in their outer shell.
- Uses: cancer treatment (radiotherapy), to check for leaks using radioisotopes (tracers) added to oil/gas.
* 5) State uses of isotopes
- There are radioactive and non-radioactive isotopes.
- Used for sterilising equipment in medical, and smoke detectors in industrial.
6) Describe an Alloy
- A mixture made up of two or more metals.
- Pure metals are too soft for certain uses, and so are mixed with small amounts of other metals to make them stronger or improve their usability.
- Example brass, mixture of copper and zinc. Brass is stronger than either copper or zinc.
ions and ionic bonds
6) Describe the formation of Ions
- Atoms become ions by electron loss or gain.
- Metals lose electrons to become cations.
- Non-metals gain electrons to become anions.
6) Describe Ionic Bonds
- Formed between metallic and non-metallic elements.
- Ionic bonds are strong electrostatic force of attraction between positive cations and negative anions.
- Ionic compounds form giant lattice structure, a regular arrangement of alternating positive and negative ions, has high melting point.
- Do not conduct electricity in solid state, as the ions are not mobile. In molten or aqueous, it can conduct electricity as the ions are now mobile.
- Usually soluble in water.
molecules and covalent bonds
7) Describe Simple Covalent Bonds
- Formed between non-metallic and non-metallic elements.
- Covalent bonds are the sharing of pairs of electrons leading to noble gas configuration.
- Usually liquid or gas with Low m.p. and b.p. due to weak intermolecular forces of attraction between molecules
- Don’t conduct electricity as there are no mobile ions/electrons.
- Usually insoluble in water
8) Describe the giant covalent structures of Graphite and Diamond
- Melting point high because structure made up of strong covalent bonds
- Don’t conduct electricity as they do not have mobile ions or electrons, except for graphite.
- Hard due to strong tetrahedral structure, but graphite is soft
Used for cutting
Strongest known substance
Made of flat sheets
Held together by weak forces
Conducts electricity as it has one free electron
* 9) Describe Metallic Bonding
- Metallic bonding is a lattice of positive ions in a 'sea of electrons'.
- Can conduct electricity due to de-localised electrons that are mobile and can move through the structure.
- Malleable as layers of ions can easily slide over each other.