2.1.1

• isotope: an atom of an element with the same number of protons but a different number of neutrons
• mass number = protons + neurons
• atomic number = number of protons in the nucleus of an atom
• ionic charge = the number of electrons lost or gained
• relative isotopic mass: mass of an atom of an isotope compared to 1/12th of the mass of an atom of carbon-12
• Democritus 5BCE: matter could only be split a certain number of times
• Dalton 1800s: atomic theory, atoms were small spheres that could not be divided
• thompson 1910: plum pudding model containing electrons
• Rutherford 1910: alpha particle experiment, discovered nucleus and that it was positively charged
• bohr 1910: electron shells around nucleus
• 1920 rutherford: proton
• 1920s: electrons are waves
• chadwick 1930: neutron
• relative atomic mass: the average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12
• relative atomic mass = (mass x abundance) / total abundance
• relative molecular mass Mr is used for simple molecules
• relative formula mass RFM is used for giant structures
• Mr and RFM can be found by adding the atomic mass of each atom
• mass spectrometry is used to determine the relative isotopic masses and abundances of isotopes
• isotopes have different physical properties
• physical properties are controlled by the number of neutrons
• relative isotopic mass = % x mass number / total % present