Chemistry

• John Dalton - all elements are composed of atoms.
• J.J Thomson discovered the plum pudding model.
• Ernest Rutherford - discovered that particles with a positive charge are protons and a particle with a negative charge is an electron.
• Neils Bohr - discovered that electrons move is specific energy levels or orbitals.
• James Chadwick - discovered that a particle with a neutral charge is a neutron.
• The atom us composed of - a nucleus with protons and neutrons and a space around the nucleus with electrons
• Atomic number [Z] - the number of protons in the nucleus also indicating the position on the periodic table
• Mass number [A] - the number of protons and neutrons in the nucleus
• Isotopes - have the same number of protons and same atomic number
• Isotopes - have different number of electrons and atomic mass
• Orbital


  A region of space in which the possibility of finding an electron is high
• Pauli's principle 


  Maximum of two electrons in each orbital provided they have opposite spin.
• Hund's rule


  No pairing in the p,d or f orbital before each orbital has at least one electron
• Valence electrons 


  Electrons on the outermost energy level
• Core electrons

  Electrons on the inner energy level