This is Mendeleev's Periodic Table from 1869. 

Explain why Mendeleev left gaps in his version of the Periodic Table. 

The nucleus of an atom contains $3$ protons and $4$ neutrons. Which statement about the atom is true? 

This is a diagram of a lithium atom. Label the diagram by choosing words from this list. 

The symbol for carbon in the Periodic Table is ${}_6{}^{12}\mathrm{C}$. Describe the electronic structure of a carbon atom. 

These diagrams show two different models of the atom. 

State two similarities and one difference between the two models.

Sodium has atomic number $11$ chlorine has atomic number $17$. Compare the structure of a sodium atom with that of a chlorine atom. 

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

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.