Key concepts of chemistry

• Atom


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


  • Protons
  • Neutrons
  • Electrons
• Protons


  Positive charge of +1
• Neutrons


  Neutral charge of 0
• Electrons


  Negative charge of -1
• Atoms always have the same number of protons and electrons</b>
• Historical atomic models


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


  Different version of an element's atom with a different number of neutrons
• Isotopes have the same number of protons and electrons, but different numbers of neutrons
• Mass number


  Total number of protons and neutrons in an atom
• Atomic number


  Number of protons in an atom
• Relative atomic mass is an average of all the isotopes of an element
• The periodic table organises elements by atomic number and their properties
• The periodic table was created by Mendeleev, who left gaps for undiscovered elements
• Ionic bond


  Bond between a metal and a non-metal
• Formation of an ionic bond


  1. Atom loses or gains electrons

  2. Atom becomes a positively or negatively charged ion

  3. Oppositely charged ions are attracted to each other
• Cation


  Positively charged ion
• Anion


  Negatively charged ion
• Ionic compound formation


  • Sodium (metal) loses 1 electron to chlorine (non-metal)
  • Oxygen (non-metal) gains 2 electrons from 2 lithium (metal) atoms
• Ionic compounds


  • Form a giant crystal lattice
  • Have high melting and boiling points
  • Can conduct electricity when molten or dissolved
• Ionic equation


  Equation showing the ions involved in an ionic reaction
• Spectator ions are ions that don't change in an ionic reaction
• Covalent bond


  Bond between non-metals where electrons are shared
• Ions


  Atoms or molecules that have gained or lost electrons, giving them a positive or negative charge
• Polyatomic ions have a charge on the whole compound
• Spectator ions


  Ions that don't change before and after a reaction
• Removing spectator ions from ionic equations

  1. Identify spectator ions

  2. Remove spectator ions from equation
• Covalent bond


  A 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
  • Cannot conduct electricity
• Graphite


  • Organized in layers that can slide over each other
  • Can conduct electricity
• Metallic bond


  Caused by metal atoms giving up their electrons which then delocalize
• Metals


  • Have high melting points due to strong electrostatic forces between metal ions and delocalized electrons
• Mole


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

  1. Identify sample mass

  2. Identify molar mass of compound

  3. Divide sample mass by molar mass
• Relative formula mass


  The total mass of a compound, found by adding the masses of its constituent atoms
• Empirical formula


  The simplest whole number ratio of atoms in a compound
• Finding empirical formula


  1. Identify masses of elements

  2. Calculate moles of each element

  3. Divide moles by smallest to get simplest ratio
• Empirical formula


  Simplest whole number ratio of atoms