Page 65 - Science Coursebook

4.2 More about the structure of the atom

Look carefully at the diagrams as the atoms get bigger.

Beryllium. Boron. Carbon.

The arrangement of electrons in an atom is often written as numbers. For example,
the electron arrangement for an atom of boron can be written as 2,3. This means
there are two electrons in the first shell and three in the next shell. The first shell

always fills up before electrons go into the second shell.

Questions
1 How many electrons are there in an atom of carbon?
2 How many protons are there in an atom of beryllium?
You will need to look at the Periodic Table to answer the following questions.
A+I 3 How many neutrons are there in an atom of boron?
A+I 4 Draw a diagram to show the structure of an atom of magnesium.
A+I 5 What is the name of the element that has electrons arranged 2,8,2?

A+I 6 Draw a labelled atomic diagram of the element fluorine.
Activity 4.2

A model of an atom

In this activity you will build a model of an atom of a particular element.
1 Cut a circle of card about 6 cm diameter; this will act as the base for the nucleus. string
2 Cut out enough small circles of about 1.5 to 2 cm in diameter to represent
twice the number of protons in red coloured paper or card, and twice the electron
number of neutrons in blue coloured card. Stick these onto both sides of
the nucleus. card
3 Cut out concentric rings of card to represent the shells of electrons.
The circles should be about 2 cm wide. proton
4 Cut out small circles, in green coloured paper, to represent twice the neutron
number of electrons. Stick these on both sides of the appropriate ring.
Assemble the model as shown in the diagram. Make a label for your atom.

Summary
• The atomic number tells you how many protons are in the atom.
• The mass number tells you how many protons + neutrons there are.

• Electrons are arranged in shells. A shell must be filled before starting
on the next one.

4 Material properties 63