chapter 2

• Protons and neutrons have a mass of 1 and electrons have a mass of 1/1836. Protons are positive, neutrons are neutral and electrons have a negative charge. The nucleus is positive, but the overall atom is neutral.
• Isotopes are atoms of the same element that have the same number of protons and electrons, but a different number of neutrons, so a different mass number
• Positive ions are also known as cations and are missing a few electrons. Negative ions are known as anions and contain more electrons than protons
• Relative isotopic mass is the mass of an isotope compared to 1/12th the mass of a carbon 12 atom.
• relative atomic mass is the weighted mean mass of an atom of an element compared to 1/12th the mass of a carbon 12
• relative atomic mass can be measured using a mass spectrometer, which measures the percentage abundance of each isotope using the mass to charge ratio of an ion.

  Calculations= sum of (percentage of ion x mass number)/ 100
• most transition metals can form several different ions, so the ionic charge is shown using roman numerals
• a binary compound( only two elements) is named by using the first element, which is usually a metal, and then the second element end in -ide
• Polyatomic ions

  1+ = NH4

  1-= OH, NO3, NO2, HCO3, MnO4

  2-=CO3, SO4, SO3, Cr2O7

  3-=PO4
• Some elements that exist as diatomic molecules include: nitrogen, oxygen, hydrogen, group 7 elements. Phosphorus can exist as p4 and sulfur can exist as s8
• state symbols-

  g = gas

  l = liquid

  s= solid

  aq = aqueous, or dissolved in water