Development of the periodic table - Webflow

Development of the periodic table

1 Describe early attempts to arrange elements in a periodic table.

2 Explain why Mendeleev was able to predict undiscovered elements and their properties.

3 Describe how elements are arranged in the modern periodic table.

Development of the periodic table '

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1:??oI* The periodic table is arranged in I columns called 1gro=up1s.

???I The groups are labelled 1, 2, transition metals, 3, 4, 5, 6, 7 and 0 (or 8).

0

12

34 5 67 1

2

transition metals

3

4

5

6

7

Key

?questions

???I All the elements in a group have similar chemical properties (e.g. group 1

consists of highly reactive metals). As a result they react in the same way. This is because all the elements in a group have the same number of electrons in their outer shell (group 1 metals all have one electron in their outer shell.

20

40

?? The elements in a periodic table are arranged in order of atomic number

calcium

starting with hydrogen at 1. Remember the atomic number is equal to the

number of protons in an atom.

20

40

&?o? TheI rows in a periodic table are called1pe=riod1s. The number of the period

tells you how many energy levels or shells an element has.

Mendeleev and the periodic table

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40

1:?.*?] Mendeleev started by arranging all the elements in order of increasing

atomic weight.

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40

?? Mendeleev would switch the order of elements so that they fitted the

calcium

patterns of elements in the same group.

???I Mendeleev also realised that some elements had not been discovered so he

would leave gaps in the periodic table.

I Summary

1 Development of th- e periodic table

=

1 Mendelee- v's period1 ic table

Key words

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Key questions

. Mendeleev was able to predict the properties of the undiscovered elements based on the other elements in the group.

i

:.*is. When Mendeleev developed his table, protons had not been discovered. The problem with basing the table on atomic weights is that the elements can appear in the wrong order due to the presence of isotopes.

::*oa Mendeleev also did not include group 0. This is because these elements are not

reactive so had not been discovered.

I Summary

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