Atoms and reactions

Atoms and reactions

1. Isotopes

   • Isotopes of the same element have:
     • Same no. of protons and neutrons
     • Different no. of neutrons in nucleus
     • Different masses
   • Different isotopes of the same element react in the same way because:
     • Chemical reactions involve electrons
     • Neutrons make no difference to chemical reactivity

2. ATOMIC (PROTON) NUMBER - the number of protons in the nucleus of an atom

3. ISOTOPES - atoms of the same element with different numbers of neutrons

4. MASS (NUCLEON) NUMBER - the number of particles in the nucleus

5. ION - a +ve or -ve charged atom or (covalently bonded) group of atoms (molecular ion)

6. Atomic masses

   • Relative Isotopic Mass
     • Same as a mass number for an isotope
   • Relative Atomic Mass
     • 'Weighted mean mass' to account for the contribution of each isotope to overall mass of an element
     • Contribution made by isotope depends on:
       • % abundance of isotope
       • Relative mass of isotope
   • Relative molecular mass
     • Mass of a molecule measured as the realtive molecular mass by comparison with carbon-12
     • Add together relative atomic masses of each atom in the molecule
   • Relative formula mass
     • Compounds with giant structures don't exist as simple molecules
     • Add together relative atomic masses of each atom making up formula unit

7. RELATIVE ISOTOPIC MASS - the mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12

8. RELATIVE ATOMIC MASS - the weighted mean mass of an atom of an element compared with one-twelfth on the mass of an atom of carbon-12

9. RELATIVE MOLECULAR MASS - the weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12

10. RELATIVE FORMULA MASS - the weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12

11. Amount of substance and the mole

    • Amount of substance
      • Symbol, n
      • Measured using unit called the 'mole'
      • Based on standard count of atoms
        • Avagadro's constant
          • No. of atoms per mole of the carbon-12 isotope
    • Mass of 1 mole of atoms of any element = the relative atomic mass in grams
    • A 'mole' is the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope
    • Molar mass - add together all relative atomic masses for each atom that makes up a formula unit
    • n = m/M

12. Types of formula

    • Empirical formula
      • Always used for compunds with giant structures
    • Molecular formula
      • Used for compounds that exist as simple molecules
        • Tells you no. of each type of atom that makes up a molecule

13. AMOUNT OF SUBSTANCE - the quantity whose unit is the mole. Chemists use it as a means of counting atoms

14. AVAGADRO CONSTANT - the no of atoms per mole of the carbon-12 isotope

15. MOLE - the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope

16. MOLAR MASS - the mass per mole of a substance. Units = g mol-1

17. EMPIRICAL FORMULA - the simplest whole-number ratio of atoms of each element present in a compound

18. MOLECULE - small group of atoms held together by covalent bonds

19. MOLECULAR FORMULA - the actual no of atoms of each element in a molecule