 Question 2. The diagram represents an atom of nitrogen. Part A. Use the words in the box to label the diagram. Electron, proton, neutron, shell, nucleus. So let's write down what we know about an atom. An atom has a nucleus which is made up of protons and neutrons. This is surrounded by shells and in these shells we find electrons. Protons are the positive, electrons are negative and neutrons are neutral. If we look at the arrows on the diagram we can see that the first arrow is pointing from a part of the atom outside the nucleus. It's pointing to a particle on a shell. Therefore this particle must be an electron. The next two arrows are coming from the central part of the atom, from the nucleus, but they are coming from two individual particles within it. Therefore these must be protons and neutrons. We can tell which is which because the proton has a positive, a charge associated with it. This is indicated by the plus sign. Part B. Draw a ring around the mass number of this atom. Let's write down what we know about the mass number. The mass number is equal to the number of protons plus the number of neutrons. The protons and neutrons are found in the centre of the atom in the nucleus. So if we count up the number of particles in the centre of the atom we find there are seven protons and seven neutrons. Seven plus seven. Fourteen. Therefore the mass number of this atom is fourteen. Part C. Oxygen has an atomic number or proton number of eight. Which diagram A, B, C or D shows the electronic structure of an oxygen atom? Let's write down what we know. The atomic number tells us how many protons are in an atom. The number of protons is equal to the number of electrons. This means we should see eight electrons in the correct diagram. We can therefore eliminate diagram C as it only has six electrons. We can also eliminate diagram D as it has ten electrons. What else do we know? We know that the first eleven atom can only hold a maximum of two electrons. This means we can eliminate diagram A because it has four electrons in its first shell. Therefore diagram B shows the correct electronic structure of an oxygen atom. It has two electrons in the first shell and six electrons in the second shell making up eight electrons. Thank you.