CHEM KEY CONCEPTS

• Atom

  Consists of a nucleus with protons and neutrons, and electrons in shells outside the nucleus
• Subatomic particles

  • Protons
  • Neutrons
  • Electrons
• Protons

  Positively charged particles in the nucleus
• Neutrons

  Neutral particles in the nucleus
• Electrons

  Negatively charged particles in the shells outside the nucleus
• Atomic models

  • Dalton's billiard ball model
  • Thompson's plum pudding model
  • Rutherford's planetary model
• Isotope

  A different version of an element's atom with a different number of neutrons
• Mass number

  The total number of protons and neutrons in an atom
• Atomic number

  The number of protons in an atom
• Relative atomic mass

  The average mass of all the isotopes of an element
• The periodic table organizes elements by atomic number and their properties
• The group number tells the number of electrons in the outer shell, and the period number tells the number of shells
• Mendeleev created the first periodic table, leaving gaps for undiscovered elements
• Ionic bond

  A bond between a metal and a non-metal, formed by the loss or gain of electrons
• Ion

  A charged particle formed by the loss or gain of electrons
• Cation


  A positively charged ion formed by the loss of electrons
• Anion

  A negatively charged ion formed by the gain of electrons
• Formation of ionic compounds

  1. Metal atom loses electron(s)

  2. Non-metal atom gains electron(s)

  3. Ions form a giant crystal lattice
• Ionic compounds

  • Have high melting and boiling points
  • Can conduct electricity when molten or dissolved
• Ionic equation

  Shows the ions involved in an ionic reaction
• Covalent bond

  A bond between non-metals where electrons are shared
• Ionic bond

  Atoms are bonded in a different way and split them up into their ions
• Polyatomic ions like OH- have a charge on the whole compound
• Removing spectator ions in ionic equations


  Remove ions that don't change before and after the reaction
• Covalent bond

  Bond between non-metals where a pair of electrons is shared
• Covalent molecules

  • Have strong covalent bonds between atoms in the molecule
  • Have weak intermolecular forces between covalent molecules
• Allotropes of carbon


  • Diamond
  • Graphite
• Diamond


  • Very hard and strong due to triangular and pyramid shape
  • Cannot conduct electricity as each carbon is bonded to 4 others with no free electrons
• Graphite

  • Organised in layers that can slide over each other making it a good lubricant
  • Can conduct electricity as each carbon is only bonded to 3 others leaving a spare electron to delocalize
• Metallic bond

  Metal atoms give up their electrons which delocalize, forming positive metal ions with strong electrostatic forces
• Mole


  A special number, 6.02 x 10^23, that links mass to the number of atoms in a sample
• Calculating number of moles

  Sample mass / mass of compound
• Relative formula mass

  Total mass of a compound, found by adding the masses of the atoms
• Empirical formula

  The simplest ratio of all the numbers in a compound
• Finding empirical formula

  Write out what is known from the question

  2. Find the mass numbers of the elements

  3. Calculate the moles of each element

  4. Divide the moles by the smallest to get the ratio
• Calculating empirical formula from mass data

  Find the mass of each element

  2. Calculate the moles of each element

  3. Divide the moles by the smallest to get the ratio
• Finding molecular formula from empirical formula and relative formula mass

  Calculate the mass of the empirical formula

  2. Divide the relative formula mass by the empirical formula mass to get a multiplier

  3. Multiply the empirical formula by the multiplier to get the molecular formula
• The periodic table is an arrangement of elements based on their atomic number
• Groups (columns) contain elements that have similar chemical properties due to having the same number of electrons in their outer shell.