# Video: GCSE Chemistry Higher Tier Pack 1 • Paper 1 • Question 2

GCSE Chemistry Higher Tier Pack 1 • Paper 1 • Question 2

08:20

### Video Transcript

An atom of phosphorus has the symbol 31 P 15. Determine the number of protons, neutrons, and electrons in this phosphorus atom.

Let’s look at the question again. The symbol 31 P 15 is in nuclide notation. Nuclide notation is a way of taking various aspects of an atom or ion and condensing them down into an easy-to-read format. Nuclide notation condenses four different aspects into super- or subscripts. These are charge, the number of atoms, the atomic number of those atoms, and the mass number of those atoms.

In this case 31 P 15, both the charge and the number of atoms are not made explicit. These are implied to be charged zero and to have only one. These are the defaults. So let’s look at what atomic number and mass number actually mean and try and figure out the number of protons, neutrons, and electrons in this atom.

For this atom, the atomic number is 15. The atomic number is the same as the number of protons in the nucleus. Therefore, the number of protons for this answer is 15. The mass number for this atom is 31. This is the same as the number of protons plus the number of neutrons in the nucleus. Therefore, to get the number of neutrons, we just have to subtract 15 from 31. That gives us our answer of the number of neutrons as 16.

But what about the number of electrons? If you recall, the charge of this atom is zero. That means that all the charges of the particles inside the atom must cancel out. If we look at the actual charge of the individual particles, you’ll recall that protons, neutrons, and electrons have a charge of plus one, zero, and minus one, respectively. Therefore, the number of electrons must balance exactly the number of protons. Therefore, the number of electrons in this answer is 15.

So for an atom of phosphorus with the symbol 31 P 15, there are 15 protons, 16 neutrons, and 15 electrons.

Why is phosphorus in group five of the periodic table?

Firstly, let’s review what a group is in the periodic table. A group is the same as a column in the periodic table. All the elements in the same group have the same valence electron configuration. So where is group five? We skip out counting the transition elements and just go one, two jump three, four, five. This is because the transition elements have a much more complicated electronic structure.

So let’s look at the valence electron configuration of each group. The elements in group one have one electron in their outer shell, like lithium. Elements in group three have three electrons in their outer shell, elements like boron.

So how many electrons in the valence shell of phosphorus are there? Well, we know from the previous question that phosphorus has 15 electrons when it’s neutral. This gives it an electron configuration of two from the first shell, eight from the second shell, and five from the third.

Just remember where phosphorus sits, just below nitrogen in group five of the periodic table. Therefore, phosphorus has five electrons in its outer shell. This is why it belongs in group five. Therefore, the answer to why is phosphorus in group five of the periodic table is phosphorus has five electrons in its outer shell.

Shown in table one are selected properties of two halogens and two transition elements. Using your knowledge and the information in table one, compare the chemical and physical properties of the halogens and transition elements.

There are two things detailed in the table for two halogens and two transition elements: the boiling points and the formulas of common compounds. Let’s start with the boiling points.

Fluorine has a boiling point of minus 188 degrees. This means that it is a gas at room temperature. Meanwhile, bromine has a boiling point of 59 degrees, which means that it is at least a liquid at room temperature. The transition elements titanium and vanadium both have very high boiling points. They also have very high melting points, meaning they are solids at room temperature.

The higher boiling point suggests that the bonds between the components of these elements are much stronger for titanium and vanadium than they are for fluorine and bromine.

Now, let’s look at the formulas of common compounds. As we can see from the formulas of sodium, fluoride, and sodium bromide, where sodium has a plus one charge, fluoride and bromide both have minus one charge. This illustrates the fact that halogens generally form negative ions.

On the other hand, the transition elements titanium and vanadium illustrate the transition elements commonly form positive ions. Chloride will have a minus one charge, meaning that the titanium and vanadium ions must have charges of two plus, three plus, and four plus.

If you recall the halogens fluorine and bromine are both strongly colored, while titanium and vanadium in their elemental forms are both silvery like most transition elements. However, when fluorine and bromine react, they tend to form white compounds, while transition elements because of their variable oxidation states have bright colors in their compounds.

There are of course exceptions. For instance, when transition elements are directly bonded to halogens, the substance is probably colored. But this is because of the transition element and not the halogen. Halogens are also highly reactive, whereas transition elements are less so. In addition to all these properties, transition elements are usually hard and dense.

So to answer this question, I’m going to express each of these points as a full sentence one by one. Transition elements generally have much higher boiling points than halogens. Transition elements generally are solids at room temperature, while halogens are generally liquids or gases. There are exceptions to this: mercury is a transition element that is a liquid at room temperature. And iodine is a halogen that’s solid, but generally this holds true.

Halogens react to form ions with minus one charge, while transition elements react to form positive ions with a range of charges. Halogens are generally colored, while transition elements are generally silvery. Halogen compounds are generally white, while transition element compounds are generally colored. Halogens are highly reactive, while transition elements are less so. Transition elements are generally hard and dense.

I gave seven statements. But as this was a six-mark question, you would only need six. You could have also talked about the halogens being diatoms with covalent bonds and the transition elements being metals. You just need to be sure that your answers are clear and concise and make good comparisons between the two groups.