Key Concepts in Chemistry

• What are three ideas John Dalton‘s theory about the atom?

  Cannot be created, divided or destroyed.

  Atoms of the same element are exactly the same and different are different.

  Atoms join with other atoms to make new substances.
• What discovery caused the original Dalton model of the atom to change?

  Subatomic particles
• How did JJ Thompson discover the electron?

  Experiments with a cathode ray tube showed the beam moving towards the positively charged plate so he knew that the particles must have a negative charge.
• Describe JJ Thompson‘s atomic model.

  Plum pudding model, negatively charged electrons scattered though a positively charged material
• Ernest Rutherford‘s gold foil experiment.

  Alpha particles shot at a sheet of gold foil, most passed straight through showing atoms mostly empty space, a few deflected and some bounced directly back, showing a small dense mass in the centre the nucleus
• How large is the nucleus compared to the atom‘s radius?

  1 / 10000
• How do you calculate the relative atomic mass of an element with different isotopes?

  (mass a x percentage) + (mass b x percentage)/100
• How did Mendeleev arrange the elements in his periodic table?

  Increasing atomic masses, similar properties in groups, left gaps for undiscovered elements
• Why was Mendeleev‘s table somewhat inaccurate?

  Isotopes were poorly understood, protons and neutrons had not yet been discovered
• What does they period (row) number of an element tell you about it?

  Same number of electron shells as the row, e.g. all elements in period 3 have 3 electron shells.
• What is an ionic bond?

  The electrostatic attraction between ions of a metal and non-metal after the transfer of electrons.
• What does it mean if an ionic compound ends in -ide?

  The compound contains 2 elements.
• What does it mean if an ionic compound ends in -ate?

  The compound contains at least three elements, one of which is oxygen
• Describe the structure of an ionic compound.

  Regular lattice structure with strong electrostatic bonds.
• What is a covalent bond?


  A bond formed between a shared electron pair and the nucleus of two non-metal atoms
• Do giant covalent structures have a high melting point?

  Yes because they have strong covalent bonds which require a lot of energy to break.
• Are metals insoluble in water?

  Yes
• Name two giant covalent structures formed from carbon atoms.

  Graphite, diamond
• Describe the structrue and properties of graphite.

  Each carbon atom joined to three others, layers of hexagonal rings of carbon atoms, weak intermolecular forces, one delocalised electron per carbon atom
• Describe and explain the properties of graphite.

  Soft/malleable because weak intermolecular forces allow layers to slide over eachother.

  Conducts electricity because there is one delocalised electron per carbon atom.
• Describe the structure and properties of a diamond.

  All carbon atoms covalently bonded to four others, very hard and high melting point.

  No delocalised electrons, so doesn‘t conduct electricity.
• Uses of graphite and why.

  Electrodes because they conduct electricity and have a high melting point.

  Lubricant because it‘s slippery from the layers sliding over each other.
• What is fullerene?

  A molecule made of carbon, shaped like a closed tube or hollow ball.
• Buckminsterfullerene (C60)


  Malleable due to weak intermolecular forces, low melting point, spherical, strong covalent bonds between carbon atoms in a molecule, large surface area
• Properties of graphene (a fullerene)

  High melting point due to covalent bonding between carbon atoms, conducts electricity because it has delocalised electrons
• Why is graphene useful in electronics?

  Extremely strong, conducts electricity, only one atom think as it is a single layer of graphite
• What bond is formed between carbon atoms and polymer molecules?

  Covalent bonds
• What are the limitations of these models showing ionic compounds?

  Dot and cross - no lattice structure or ionic bonds.

  2D diagrams - only shows one layer, doesn‘t show formation of ions.

  3D diagrams - shows spaces between the ions, doesn‘t show charges.
• What are the limitations of the these models showing covalent bonds?

  Dot and cross - doesn‘t show relative sizes of atoms or intermolecular forces.

  Ball and stick - bonds shown as sticks rather than forces, doesn‘t show how covalent bonds form.
• What is the empirical formula and how do you calculate it?

  The smallest whole number ratio of the atoms of each element in a compound, reacting masses or percentage composition can be used to calculate it
• Describe an experiment to work out the empirical formula of magnesium oxide.

  Weigh a sample of magnesium and heat it in a crucible.

  Weigh the mass of magnesium oxide at the end, opening the crucible every few minutes during the experiment.

  Calculate the mass of oxygen and then the moles.

  Work out the whole number ratio of moles of magnesium to moles of oxygen.
• What is the law of conservation of mass?

  No matter is lost or gained during a chemical reaction
• If a reaction occurs in a closed system what happens to the mass?

  It stays constant.
• How do you calculate concentration in g/$dm^3$


  Concentration(g/dm^3) = mass/volume(dm^3)
• Avagadro‘s constant.

  The number of atoms, molecules or ions in one mole of a subtance, 6.02 x 10^23
• What is a limiting reagent in a chemical reaction?

  The chemical used up first in a reaction, preventing the formation of more product - so excess is typically used.