chemistry topic 1

• Atoms


  Particles of matter

  made up of a nucleus

  surrounded by electrons
• Subatomic particles

  • Neutrons
  • Protons
  • Electrons
• Neutronscharge

  Neutral charge
• Protons chagre

  Positive charge
• Electronscharge

  Negative charge
• RAM (Relative Atomic Mass)

  Mean atomic mass of an element relative to carbon 12
• Calculating RAM

  1. Isotope mass x isotope abundance

  2. Add up for all isotopes

  3. Divide by 100
• Isotopes

  Different atoms of the same element that have different numbers of neutrons but the same number of protons
• Dalton thought atoms were solid spheres that make up elements
• Thomson's plum pudding model

  • Discovered subatomic particle (electron)
  • Electron has mass and charge
• Rutherford's nuclear model

  • Discovered the nucleus is positively charged
  • Electrons orbit the nucleus in empty space

  golden leaf experiment - fired alpha particles at it some bounced back, deflected + went thru
• Bohr's model

  • Electrons are fixed to shells with specific energy levels
  • Disproved the nuclear model because electrons would collapse into the nucleus
• Mendeleev's periodic table

  • Ordered by increasing atomic mass
  • Grouped by similar chemical properties
  • Accounted for isotopes having different masses
• Periodic table structure

  • Periods (arranged in ascending atomic number)
  • Groups (arranged by similar chemical properties)
• why are P + E equal in the atom

  bc P have a +ive charge which cancel out with e- -ive charge

  no overall charge

  not true in an ion bc they have an overall charge
• Ions

  Atoms or groups of atoms with a positive or negative charge
• Formation of ions

  1. Atoms want to be stable

  2. Cations have a positive charge, atoms lose electrons

  3. Anions have a negative charge, atoms gain electrons
• Ionic bonding


  Strong attraction between metals and non-metals
• Formation of ionic compounds

  1. Metal atoms lose electrons to form positive ions

  2. Non-metal atoms gain electrons to form negative ions

  3. Ions form a stable outer shell
• Ionic compounds


  Formed by the movement of electrons
• Representation of ionic compounds

  • Dot and cross diagrams
• Ionic lattice structure

  • Regular arrangement of ions
  • Held by strong attraction between opposite charges
  • Similar species
• High melting and boiling points of ionic compounds

  Due to the strong attraction between oppositely charged ions, a lot of energy is needed to overcome this
• Ionic compounds

  • Do not conduct electricity in solid state as ions cannot move freely
  • Conduct electricity when molten or dissolved in water as ions are free to move
• Advantages and disadvantages of different models

  • Ball and stick - simple, don't show shape or size
  • Space-filling - show size and arrangement, but not outer layer
  • Dot and cross - show how compounds/molecules are formed and where electrons came from
  • Realistic 3D - show shape of lattice/molecule, but can be misleading and not to scale
• Covalent bonding


  Strong bond formed when a pair of electrons is shared between two atoms
• Simple molecular substances with covalent bonds


  • Strong intramolecular bonds, weak intermolecular forces
  • Low melting and boiling points due to weak intermolecular forces, only a small amount of energy needed to break them
  • Do not conduct electricity as there are no free ions/electrons
• Covalent compounds

  • H2
  • H2O
  • CO2
  • CH4
• Dot and Cross Diagrams

  • Useful for illustrating the transfer of electrons
  • Indicates from which atom the bonding electrons come from
• Dot and Cross Diagrams

  • Fails to illustrate the 3D arrangements of the atoms and electron shells
  • Doesn't indicate the relative sizes of the atoms
• Ball and Stick Model


  • Useful for illustrating the arrangement of atoms in 3D space
  • Especially useful for visualizing the shape of a molecule
• Ball and Stick Model

  • Fails at indicating the movement of electrons
  • The atoms are placed far apart from each other, which in reality is not the case as the gaps between atoms are much smaller
• 2D Representations of Molecules

  • Displayed formulae are 2D representations and are basically simpler versions of the ball and stick model
  • Adequately indicate what atoms are in a molecule and how they are connected
• 2D Representations of Molecules


  • Fail to illustrate the relative sizes of the atoms and bonds
  • Cannot give you an idea of the shape of a molecule and what it looks like in 3D space
• 3D Representations of Ionic Solids

  • 3D drawings and models depict the arrangement in space of the ions
  • Also show the repeating pattern in giant lattice structures
• 3D Representations of Ionic Solids

  • Only illustrate the outermost layer of the compound
  • Are difficult and time-consuming to draw