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Atomic Structure and the Periodic Table

Development of the periodic table

  • 3 things to know
  • Paper 1

Overview

How early tables ordered elements by atomic weight and why they were faulty, Mendeleev's gaps and reordering, how his predictions were confirmed, and how isotopes explained the anomalies.

What you need to know

Answer each one before you reveal it.

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Key term

Besides leaving gaps, what else did Mendeleev do to make his table work?

Key term

What eventually happened to the gaps Mendeleev left?

Key term

Which later discovery explained why ordering by atomic weight was not always correct?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Before protons, neutrons and electrons were known, in what order did scientists arrange the elements?

    Model answer

    They arranged them in order of their atomic weights.

  2. 2

    Why could the earliest classifiers of the elements not use atomic number?

    Model answer

    Because subatomic particles had not yet been discovered, so proton numbers were unknown.

  3. 3

    Give two faults with the early periodic tables.

    Model answer

    They were incomplete, and some elements ended up in groups where their properties did not fit.

  4. 4

    Why were some elements misplaced when strict atomic weight order was followed?

    Model answer

    Because that order did not always put elements with similar properties in the same column.

  5. 5

    Why were the early tables incomplete?

    Model answer

    Because many elements had not yet been discovered, so there was nothing to place in those positions.

  6. 6

    What did Mendeleev do about elements he believed had not yet been discovered?

    Model answer

    He left gaps for them in his table.

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Atomic Structure and the Periodic Table
Bonding, Structure, and the Properties of Matter
Chemical Analysis
Chemical Changes

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ALithium compounds produce a crimson flame.
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Base means any substance that neutralises an acid.
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