Unit 1 - Chemistry

• Element


  A substance that's made of only one type of atom
• Atom


  • The basic unit of an element, consisting of a nucleus containing protons and neutrons, and one or more electrons bound to the nucleus
• Compound


  A substance formed by the chemical combination of two or more elements in definite proportions
• Types of compound


  • Covalent
  • Ionic
• Ion


  An atom or molecule that has gained or lost one or more electrons
• Metal ions are positive, non-metal ions are negative
• Electron configuration


  Whereabouts the electrons are in an atom
• Atom


  • Electrons whizzing around it
  • Electrons in shells
  • Shells numbered n=1, 2, 3, etc.
• Shells


  • Have subshells
  • Subshells are s, p, d, f
• Subshells


  • Made of orbitals
  • Each orbital can hold a maximum of 2 electrons
• Filling up electron configuration

  1. Fill up lowest energy shells first

  2. Fill up s orbitals before p, p before d, etc. WE HAVE 1S 2S 2P 3S 3p 4S 3d you fill up the 4S before 3d

  3. Fill up orbitals with up and down spinning electrons
• Electron configuration of Fluorine

  • 1s2 2s2 2p5
• Electrons fill up orbitals in pairs, with one electron spinning up and the other down
• Electron configuration of Calcium

  • 1s2 2s2 2p6 3s2 3p6 4s2
• Electron configuration of Magnesium ion (Mg2+)


  • 1s2 2s2 2p6
• Electron configuration of an ion is the same as the neutral atom, minus the number of electrons lost/gained
• Group 1 elements form +1 ions, Group 2 form +2 ions, Group 7 form -1 ions, Group 0 (inert gases) do not form ions
• Ion


  An atom or molecule which has gained or lost one or more electrons
• Ionic bond - Sodium losing an electron

  1. Sodium wants to lose an electron to have a full outer shell

  2. Chlorine wants to gain an electron to have a full outer shell

  3. Sodium gives an electron to chlorine

  4. Sodium becomes a positive ion

  5. Chlorine becomes a negative ion
• Positive ion (cation)


  An atom that has lost one or more electrons, resulting in more protons than electrons
• Negative ion (anion)


  An atom that has gained one or more electrons, resulting in more electrons than protons
• Ionic compound


  A compound formed by the electrostatic attraction between positive and negative ions, resulting in a giant, regular structure (lattice)
• Sodium chloride (NaCl) is an ionic compound
• Ionic compounds


  • Have a giant, regular structure (lattice) with positive and negative ions arranged in rows and columns
  • The strength of the ionic bond depends on the charge of the ions and the distance between them
• Cation


  A positive ion
• Anion


  A negative ion
• Polyatomic ion


  An ion composed of more than one atom, e.g. CO3^2-, SO4^2-, NO3-, OH-
• Strength of ionic bond


  • Depends on the charge of the ions (higher charge results in stronger bond)
  • Depends on the distance between the ions (smaller distance results in stronger bond)
• Covalent bond

  • the strength of covalent bonds depends on how much distance seperates the bonded nuclei.
  • Short covalent bonds are stronger than long covalent bonds (hydrogen, nitrogen, oxygen, fluorine)
  • Multiple bonds are stronger than single bonds (double bonds)
• A dative bond

  Two pairs of electrons come from one atom/element. It is a shared pair of electrons
• • More shells mean that the nucleus is further away so the attraction is weaker (UP DOWN periodic table)
  • More protons so this mean that nucleus is more attractive to electrons (LEFT RIGHT - across period, periodic table)
  • Group 0 is unreactive, don't take part in bonding
  • As we go down a group the electronegativity gets weaker
• Metallic bonding - metal

  The attraction between the positive metal ions and the delocalised electrons holds the cell together
• Physical properties of metal

  Good conductors of heat

  Good conductors of electricity

  Malleable

  Ductile

  • At higher temperatures, the metal atoms vibrate more, the pass the vibrations on
  • Free electrons carry energy to metal
• Group 1 - Melting point


  Decreases as we go down the group

  The atoms are bigger because they have more shells

  The distance between the nucleus and the delocalised electrons are bigger

  The forces holding the structure together are weaker

  If they are further away from the nuclei then the force holding it together will be useful
• Group 2 - melting points

  They have higher melting points than group 1

  There are 2 delocalised electrons in each atom

  There are MORE delocalised electrons

  The metal ions have more positive charge

  The metallic bonding is stronger
• Intermolecular forces


  Forces between molecules, not forces inside a molecule
• Intermolecular forces


  • Van der Waals forces
  • Permanent dipole-dipole forces
  • Hydrogen bonds
• Van der Waals forces

  1. Electrons are not evenly distributed around an atom

  2. Temporary dipole forms with positive and negative ends

  3. Molecules with temporary dipoles can attract each other

  
  

  • They are very weak
  • The attraction only lasts for a very short time
  • It is a temporary dipole
  • The electrons in this atom are not evenly distributed i.e. one side of atom may be + or -
  • For a very short time, the positive and negative ends of molecules or atoms may attract while the dipole exists
• Permanent dipole-dipole forces


  • Molecules have a permanent dipole due to the atoms in it having different electronegativities (+ and -)
  • Positive and negative ends of different molecules attract each other
  • Permanent dipole-dipole attraction
• Hydrogen bonds


  • Special case of permanent dipole-dipole forces
  • Occur when hydrogen is bonded to fluorine, oxygen or nitrogen
  • Creates a large dipole that allows strong attraction between molecules
  • Water molecules have a large dipole, so they attract each other with hydrogen bonds
  • Small and highly electronegative