key concepts

• reactants

  left-side of a chemical reaction
• products


  right-side of a chemical reaction
• word and symbol equations show what?

  reactants and products of a chemical reaction
• word equations for reactions eg.

  magnesium + oxygen --> magnesium oxide
• isotopes


  atoms with the same number of protons but a different number of neutrons (same atomic number different mass number)
• ion


  any atom that carries a positive or negative charge
• anions


  negative ions- formed when atom or molecule gains electrons

  formed from non metal atoms
• cations

  positive ions- formed when atom or molecule loses electrons

  formed from metal atoms
• ions ending in -ate

  negative ions containing oxygen and at least one other element
• ions ending in -ide

  negative ions containing only one element
• ionic bonding


  involves the transfer of electrons between atoms to form electrons
• ionic compound


  -held in giant lattice by strong electrostatic forces

  -high melting and boiling point because a lot of energy is needed to overcome the strong electrostatic forces that hold the ions together.

  -dissolve easily in water

  -solid ionic compounds CANNOT conduct electricity but when melted or dissolved it CAN conduct electricity as the ions are free to move
• dot and cross diagrams (ionic compounds)

  pros: shows how ionic compounds are formed

  cons: doesn't show the structure, relative sizes of atoms, or arrangement
• 3D models (ionic compounds)

  pros: shows relative sizes of ions and regular patterns.

  cons: only let you see the outer layer of the compound
• Ball and stick models (ionic compounds)

  pros: shows regular pattern of ions, arrangement, may show relative sizes.

  cons: is not drawn to scale, and suggests there are gaps between ions when in reality there are not.
• covalent bond


  pair of electrons shared between two atoms.

  -non metals form these by sharing electrons to fill their outer electron shell.
• dot and cross (COVALENT)

  pros: shows which atoms the electrons come from.

  cons: don't show relative sizes
• Displayed formula (covalent)

  pros: shows how they are connected in large molecules

  cons: don't show the 3D structure.
• 3D and ball and stick models (COVALENT)


  -pros: show shape of the molecule and the bonds as well as the atoms.

  -cons: confusing for large molecules, suggest big gaps between atoms when in reality this is where the electron clouds interact. Also don't show where the bonds have come from, and NOT drawn to scale
• what forms when atoms join together through covalent bonding?

  simple molecules
• simple molecules


  not much bigger than atoms

  -tend to have low melting and boiling points because the intermolecular forces are weak, so not much energy is needed to overcome them.

  -no free ions or electrons so they do not conduct electricity.
• polymers


  large covalent molecules made up of repeating carbon-based units eg. poly(ethene)
• giant covalent structures(GCS)


  made up of lots of atoms that are all bonded to each other by strong covalent bonds.

  -do not dissolve in water and do not conduct electricity.

  -very high melting and boiling points because large amounts of energy are needed to break all the strong covalent bonds that hold the atoms together
• diamond and graphite


  forms of carbon that have giant covalent structures
• diamond(carbon based)(GCS)


  forms 4 covalent bonds

  -forms a very rigid structure making it hard

  -very high melting points because the strong covalent bonds take a lot of energy to overcome.

  -does not conduct electricity because there are no free electrons or ions
• graphite (carbon based)(GCS)


  -forms 3 of the 4 covalent bonds

  -sheets of carbon atoms arranged in hexagons

  -weak intermolecular forces so they can move over each other making them soft and slippery (lubricating material)

  -high melting points because the covalent bonds in the layers take a lot of energy to break

  -since 3 of the 4 outer electrons are used, there is one delocalised electron which can conduct electricity to make electrodes
• graphene(GCS)


  -sheet of carbon (one atom thick)

  -network of covalent bonds making it very strong

  -contains delocalised electrons and can conduct electricity through the whole structure.

  -used in electronics
• fullerenes (GCS)


  -hollow molecules of carbon (tubes or balls)

  -buckminsterfullerene: molecular formula C60 and forms a hollow sphere . It is a stable molecule and also forms soft brownish-black crystals
• metals consist of what?

  giant structures in which the atoms are held together by delocalised electrons, this means that metals can conduct electricity and heat.

  -high melting and boiling points because large amounts of energy are needed to break the strong electrostatic forces between the metal atoms and delocalised electrons.

  -shiny solids at room temperature and pressure

  -malleable because in a metal the atoms are arranged in layers that can slide over each other.

  -high densities
• differences between non-metals and metals

  Non metals: found at the top and right side of periodic table. Wide range of chemical and physical properties, dull looking, brittle, lower boiling points, don't generally conduct electricity. Form COVALENT BONDS and GAIN electrons to form outer shells.

  Metals: undergo metallic bonding, found at bottom left of periodic table, LOSE electrons to gain fuller outer shells
• conservation of mass


  during a chemical reaction, no atoms are destroyed and no atoms are created. This means there are the same number and types of atoms on each side of a reaction equation
• precipitation reaction


  the mass of a closed system, such as a precipitation reaction occuring in a stoppered conical flask, does not change during a reaction
• mass of the products in a reaction is equal to what?

  equal to the mass of the reactants
• why would the mass in a reaction seems to increase?

  because at least one of the reactants is a gas, and all the products are solids, liquids or solutions
• why would the mass in a reaction seems to decrease?

  because at least one of the products is a gas, and all the reactants are solids, liquids or solutions
• concentration of a solution is determined by?

  the amount of dissolved substance and the volume of the solution
• limiting reactant


  the reactant that gets used up first in a chemical reaction
• avogadro's constant


  6.02 × 1023

  amounts in chemistry can be measured by this.

  The number of particles (atoms,ions or molecules) in one mole of any substance is equal to Avogadro's constant.
• The Mr (relative formula mass) of a substance is the same as what?

  as the mass (in grams) as one mole of the Avogadro's constant
• Rutherford

  1.Rutherford discovered that alpha particles could bounce back off atoms

  2. Rutherford discovered that an atom's mass is concentrated in the atom's centre.

  3 Rutherford called the atom’s centre the nucleus.4

  Rutherford discovered that the nucleus contained positively charged particles called protons.

  5 Rutherford's model was called the nuclear model.