CHEM 2060CHEMISTRY- AS AS-Level Chemistry (New Spec) Notes. AS-LEVEL CHEMISTRY NOTES

SECTION 1: Atoms & Reactions 1 Atomic structure & Isotopes • Atoms are made up of protons, electrons and neutrons • Neutral atoms have the same number of protons and electrons • You can work out numbers of protons, electrons and neutrons from the element symbol • To find the total number of electrons for positive ions take away the same number of electrons from the atom (e g 3 from a 3+ ion) and for negative ions add the same number of electrons Particle | Position | Relative Mass | Charge Proton Nucleus 1 0 +1 Neutron Nucleus 1 0 0 Electron Shells around nucleus 1/2000 -12 Isotopes • Isotopes are atoms of an element with the same number of protons, but different numbers of neutrons • They have the same numbers of electrons and identical chemical reactions as a result • The atomic number is often omitted because it stays the same and the element symbol indicates how many protons there are 8 3 Relative Masses • The relative isotopic mass is the mass of an atom of an isotope compared with the mass of 1/12th an atom of 12C • The relative atomic mass, A r, is the weighted mean mass of an atom compared with 1/12th of the mass of an atom of 12C 4 Mass spectrometry • Mass spectrometry allows the masses of individual molecules or isotopes to be determined by turning substances into positive ions and measuring their mass/charge (m/z) ratio • Mass spectra plot m/z against percentage abundance • Number of isotopes can be identified by number of peaks • Each peak represents an isotope • To find the relative atomic mass multiply each isotopic mass by percentage abundance, add the results together and divide by 100 5 Relative molecular mass • Relative molecular mass, M r, is the mass of all the atoms in a molecule of a simple molecular substance • It’s found by adding up the relative atomic masses of all atoms in a molecule • Relative formula mass is the mass of one formula unit of a compound that forms a giant structure e g NaCl • It’s found in exactly the same way as Mr 9 SECTION 2: Compounds, Formulae & Equations 1 Ionic formulae • The formulae of ionic compounds can be found by balancing the charges of the individual ions that make it up • You need to know the charges of the specific ions and groups of the periodic table shown below • Find the charges of the ions in a compound and multiply up the number of moles of positive and negative ions until they balance +1 | +2 | +3 | -3 | -2 | -1