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What does it mean?

What does it mean?. 11 This is the atomic number :-the no. of protons Na This is the symbol for the element 23 This is the relative atomic mass. Objectives. To be able to read data from the periodic table To learn how to calculate relative molecular masses

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What does it mean?

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  1. What does it mean? 11 This is the atomic number :-the no. of protons Na This is the symbol for the element 23 This is the relative atomic mass

  2. Objectives • To be able to read data from the periodic table • To learn how to calculate relative molecular masses • To understand the significance of Avogadro’s number and the mole • To carry out calculations on numbers of particles

  3. Give the Relative Atomic Masses of the Following • Sulphur • Chlorine • Barium • Nitrogen • Uranium • Potassium

  4. What does Relative mean? The mass of an atom is measured relative to 1/12 the mass of a carbon 12 atom. It needs to be measured against 1 so why not use hydrogen which has a mass of 1? Hydrogen is a reactive colourless gas and is difficult to work with. Carbon is a stable abundant element and so is used as a comparison

  5. Relative Molecular Mass This is the masses of all the atoms in a formula added up. Eg carbon dioxide has the formula CO2 C has RAM 12 O has RAM 16 So 12 +(2 x 16) = 44 RMM of CO2 = 44

  6. Relative Molecular Mass:- Work out the following • NaCl • MgO • H2SO4 • HNO3 • Al2(SO4)3 • NH4Cl

  7. Activity:- Measure the mass of a crystal of sugar • Use the balance to measure the mass of a single crystal • Can you do it? • Talk to your partner and work out a way to do it.

  8. How did you get on? I’m guessing you all weighed out quite a lot of sugar and did some simple arithmetic???????? Well, atoms are too small to weigh out so chemists use a large number of of them for convenience This called AVOGADRO’S NUMBER after the clever bloke who thought the scheme up. The NUMBER IS 6 X 10 23 That’s 6 and 23 zeros! The other name for this number is a MOLE

  9. The Mole Not a small furry animal:- It’s a really important measurement in chemistry! It is 6 x 10 23 particles It is also the Relative Molecular mass in grams of a compound or element Eg. 6 X 10 23 atoms of Mg = 1 mole of magnesium metal atoms 6 x 10 23 molecules of CO2 = 1 mole of carbon dioxide 6 x 10 23 Br- ions = 1 mole of bromide ions

  10. Avogadro’s number How many particles in 2 moles of particles? 2 x (6 x 10 23) = 12 x 10 23 How many atoms in 0.5 moles Mg atoms? 0.5 x (6 x 10 23) = 3 x 10 23 How many atoms in 1 mole of CO2 molecules? CO2 has 3 atoms in a molecule so 3 x (6 x 10 23) = 18 x 10 23

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