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= (a) The table shows data about the physical properties of some elements.

Appearance at Melting point Boiling point

room temperature

in °C

in °C

green gas

red-brown liquid

dark grey solid

shiny solid

shiny solid

shiny solid

Element

Chlorine

Bromine

lodine

Lithium

Sodium

Potassium

-101

-7

114

180

97.8

63.5

-34

59

184

1342

883

759

Does the element

conduct electricity?

no

no

no

yes

yes

yes

Mendeleev put these elements into two groups in the Periodic Table.

He used their similarities and differences to put lithium, sodium and potassium in one group.

He put chlorine, bromine and iodine into another group.

Discuss which data in the table support, and which data do not support, Mendeleev's idea

of organising these elements into the two groups.

a The table shows data about the physical properties of some elements Appearance at Melting point Boiling point room temperature in C in C green

Answer :

Mendeleev's grouping is supported by similarities in appearance, melting, and boiling points, but inconsistencies in conductivity and the properties of iodine challenge his concept of strict periodicity.

Mendeleev's organization of elements into groups was based on similarities in physical and chemical properties. Analyzing the data in the table, several aspects support Mendeleev's grouping while others present challenges.

Melting and Boiling Points:

Mendeleev observed that elements in the same group tend to have similar physical properties. The data for chlorine, bromine, and iodine, all halogens in the same group, shows a progressive increase in melting and boiling points, supporting Mendeleev's idea.

Similarly, lithium, sodium, and potassium, alkali metals in the same group, display a consistent trend of decreasing melting and boiling points.

Appearance at Room Temperature:

Mendeleev considered the appearance of elements. The halogens (chlorine, bromine, iodine) share a similar appearance at room temperature, reinforcing their placement in the same group.

The alkali metals (lithium, sodium, potassium) also share a shiny appearance, supporting their grouping.

Conductivity:

Mendeleev likely considered electrical conductivity. The alkali metals all conduct electricity, aligning with Mendeleev's grouping. However, the halogens do not conduct electricity, which presents a deviation.

Inconsistencies:

The significant difference in melting and boiling points between iodine and the other halogens challenges Mendeleev's concept of strict periodicity.

In summary, Mendeleev's grouping is supported by similarities in appearance, melting and boiling points within each group. However, the variation in conductivity among halogens and the notable anomaly in iodine's physical properties highlight some inconsistencies in Mendeleev's initial organization.

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Rewritten by : Jeany

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