This is Mendeleev's Periodic Table from 1869. Explain why Mendeleev left gaps in his version of the Periodic Table.

Mendeleev left gaps in his version of the periodic table to place elements that were not known at that time. Mendeleev arranged the elements with the increase of their atomic masses and with the repetition of similar properties. On the basis of these chemical and physical properties of the elements next to a gap, Mendeleev could predict the properties of the undiscovered elements. Hence, Mendeleev left spaces for the undiscovered elements. For example, gallium, germanium and scandium were not known during that time but all these elements were discovered later and could be placed in the gaps predicted for them.

E M B I B E

Cambridge Lower Secondary Science Stage 9: Workbook>Chapter 5 - The Periodic Table>Exercise 2>Q 1

MEDIUM

Lower Secondary Stage 9

IMPORTANT

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Neon is in Group $18$ of the Periodic Table. Argon is below neon in the group. Which of these statements is true?

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Important Questions on The Periodic Table

HARD

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Workbook>Chapter 5 - The Periodic Table>Exercise 2>Q 4

Read the following information about three Group $17$ elements.

At room temperature:

• bromine is a brown liquid

• iodine is a purple-black solid

• chlorine is a green gas.

Write down in order of increasing atomic number these three Group $17$ elements. Give a reason for your answer.

HARD

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Workbook>Chapter 5 - The Periodic Table>Exercise 2>Q 5

Magnesium and calcium are both in Group $2$ of the Periodic Table. Magnesium is above calcium. When magnesium is added to hydrochloric acid you can see bubbles of hydrogen gas. Predict what you will observe when calcium is added to some hydrochloric acid.

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Workbook>Chapter 5 - The Periodic Table>Exercise 2>Q 6

Explain why elements in the same group of the Periodic Table have similar chemical properties.

MEDIUM

Lower Secondary Stage 9

IMPORTANT

Cambridge Lower Secondary Science Stage 9: Workbook>Chapter 5 - The Periodic Table>Exercise 2>Q 7

This is Mendeleev's Periodic Table from 1869.

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