Chemistry

• Periods are the horizontal rows of the periodic table. They are numbered from 1 to 18.
• Groups are vertical columns of elements in the periodic table.
• The atomic structure consists of 2 electrons in the first shell and 8 in the others
• Electron shells contain subshells which are a substructure within the shell. They are designated by the letters s, p, d and f (derived from the field of spectroscopy)

  s = one orbital, 2 electrons

  p = 3 orbitals, 6 electrons

  d = 5 orbitals, 10 electrons

  f = 7 orbitals, 14 electrons
• Aufbau Principle - shells of lower energy level get filled first. eg. 1's, 2's, 3's
• Hunds Rule - when you fill a subshell with more than one orbital (p, d, f) you first fill each orbital with a single electron with the same spin detection
• Pauli Exclusion Principle - 2 electrons in the same orbital spin in opposite directions.
• Atomic Radius - the radius of the atom

  Trends - increases as you move down a period, decreases left to right
• Ionisation energy - the energy needed to remove an electron from an atom

  Trends - smaller atoms have a higher ionisation energy as electrons are held closely to the nucleus. Increases left to right
• Electronegativity - a measure of an atoms' attraction to electrons

  Trends - increases left to right and bottom to top
• Stable Atoms - Atoms are the most stable when their valence shell (outer shell) is full of electrons. Atoms gains stability when they lose electrons and then become known as ions.
• Atoms that lose electrons become positively charged
• Atoms that gain electrons become negatively charged
• Covalent compounds are formed when two or more non-metals react together. The covalent compound is actually made of molecules, and the name given depends on the structure of these molecules.
• For two substances to react together, they have to bump into each other. This is called a collision. If there are many collisions then the rate of reaction is fast. If there are few collisions then the rate of reaction is slow
• We measure how fast a reaction is taking place by looking at how fast something is used up (reactants) or how fast something is made ( products)
• Exothermic reactions give out energy. There is a temperature rise.
• Endothermic reactions take in energy, there is a temperature drop