Draw a diagram that represents the electronic arrangement of a fluorine atom.

Electrons are arranged in different shells (sometimes described as an energy levels) around the nucleus with the innermost shell being filled first and then working outwards. The first shell can hold a maximum of 2 electrons before it is full and the next shells can hold up to a maximum of 8 electrons. For most GCSE courses only configurations up to calcium are required: 2,8,8,2.

To work out how many electrons an atom has just look at the atomic number on the periodic table, from this we can see that fluorine atoms have 9 electrons.
From the number of electrons, the electronic configuration can be worked out using the two different methods below:

Method 1: Look at the atomic number of fluorine on the periodic table = 9.
If the first shell can only hold 2 electrons then the second shell must hold 7 electrons.

Method 2: Find the element in the periodic table. Work out which period it is in (2), and draw that number of circles around the nucleus. Work out which group the element is in and draw that number of electrons in the outer circle/shell (7)

Therefore, fluorine would have 2 shells around the nucleus. The first shell holds 2 electrons and the second shell holds 7 electrons.
The diagram would use dots/crosses to represent the electrons.