Molecular Formulas

1
Molecular Formulas Relative Atomic Mass

• The Use of Avogadros Hypothesis

2
Avogadros Hypothesis (1811)

• Equal volumes of gases contain equal numbers of
  particles.

3
Waters Formula

• Two volumes of hydrogen combine with precisely
  one of oxygen.
• This meant waters molecular formula was H2O.
• Molecular formula how elements combine and in
  what ratios to form compounds.

4
The Mole

• Mole an amount of a substance
• Another way to measure atoms
• 2 moles of H combine with 1 mole of O to form 1
  mole of water

5
Relative Atomic Mass

• Avogadros hypothesis also provided a way of
  determining relative atomic masses.
• H atom relative mass of 1
• O atom relative mass of 16
• O atoms weighed 16 times that of H atoms.

6

• By 1860, a list of 60-some elements had been
  developed including their
• Properties
• Relative atomic masses
• Known molecular formulas that they formed
• It was found that
• Oxygen usually combined with 2 atoms of another
  element
• Nitrogen with 3
• Carbon with 4

7
The Periodic Table

• Dmitri Mendeleev tried to make sense of this list
  organize all the elements into a useful table.
• But, it was no easy task.