Starter quiz
- Which statement accurately describes the atomic number of any given element?
- the atomic number represents the number of protons + neutrons
- the atomic number represents the number of neutrons
- the atomic number represents the number of protons + electrons
- the atomic number represents the number of protons ✓
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- True or false: The atomic mass number of an element is listed on the periodic table.
- True
- False ✓
- Match each term with its correct definition.
- Atomic Number⇔number of protons in the nucleus of an atom, determining the element ✓
- Atomic Mass Number⇔sum of the number of protons and neutrons in the nucleus of an atoms ✓
- Relative Atomic Mass⇔average mass of an element's isotopes, based on their abundances ✓
- Isotopes of the same element have the same atomic number because they contain the same number of protons. However, they have different relative atomic masses due to varying numbers of ______.
- 'neutrons' ✓
- If an element has an atomic number of 8 and an average atomic mass of 16.0, which element is it?
- 'oxygen' ✓
- The ______ number is always a whole number because it represents the fixed number of protons in the nucleus of an atom.
- 'atomic' ✓
Exit quiz
- What does the relative atomic mass (RAM or Ar) compare the mean mass of an atom to?
- 1/12 of the mass of an oxygen-16 atom
- the mass of an electron
- 1/12 of the mass of a carbon-12 atom ✓
- the mass of a proton
-
- Order the following steps to calculate the RFM of a compound correctly. Start with the periodic table.
- 1⇔use the periodic table to find the relative atomic masses of each type of atom
- 2⇔identify the number of each type of atom in the formula
- 3⇔calculate the number of atoms × the relative atomic mass value for each element
- 4⇔add up the total relative atomic masses of all the atoms
- What is the relative formula mass (RFM) of water (H₂O)?
- 18.0 ✓
- 16.0
- 17.0
- 19.0
- 20.0
-
- Calculate the RFM of carbon dioxide (CO₂)
- '44.0' ✓
- To calculate the percentage by mass of an element in a compound, you need:
- the RFM of the compound and the RAM of the element ✓
- the atomic number of the element
- the total number of electrons in the compound
- the number of protons in the element
-
- What is the percentage by mass of hydrogen in water (H₂O)? Give your answer to four significant figures.
- '11.11 %' ✓
Worksheet
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Lesson Details
Key learning points
- The relative atomic mass is the mean mass of an atom compared to 1/12 of the mass of a carbon-12 atom.
- The relative formula mass (RFM or Mr) is the sum of the relative atomic masses of all the atoms in a chemical formula.
- %mass of an element in a compound = (relative mass of element in compound ÷ RFM of compound) × 100
Common misconception
Pupils may use the atomic number rather than mass when calculating the relative formula mass. Also, the number of atoms can be missed for the percentage of an element in a compound.
Emphasise that atomic mass is the larger number for each element on the periodic table and encourage pupils to use the key present to help them identify the mass.
Keywords
Relative atomic mass - RAM is the mean mass of an atom relative to 1/12th the mass of an atom of carbon–12.
Relative formula mass - (RFM or Mr) is the sum of the relative atomic masses of all the atoms in a chemical formula.
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