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
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.