The following nuclear equation shows neutron emission by boron-18. Boron-18 decays to an element X and emits a neutron. What is the name of element X? What element symbol should replace X?
Okay, so in this question, as we’ve mentioned already, we’ve got a decay equation showing how boron-18 decays. What that specifically means is that we’ve got an atom of boron which has a mass number of 18. And it decays to another element which has a mass number of 17 and also emits a neutron. Now, the two questions that we’ve been asked here both pertain to the element X in this reaction. Specifically, what the element’s name is and which element symbol should be replacing the letter X in the decay equation.
Now, to answer that question, let’s first recall that an element is defined by the number of protons in its nucleus. And the number of protons in an atomic nucleus is given by the atomic number which is written to the bottom left-hand side of the element symbol. Which, in this case, is B standing for boron. And we know, by the way, that this atom is representing boron because the top statement tells us that the nuclear equation shows new neutron emission by boron-18. And so, this is a boron-18 atom which also has an atomic number of five.
Now, because the atomic number refers to the number of protons in the nucleus of, let’s say, an atom. This means that if this atom with five protons is boron, then this atoms with five protons, once again, must also be boron. In other words then, in response to the first question, the name of element X is boron.
Now, moving on to the second question, we’ve been asked to find which element symbol should replace X. Now, because we know X is representing an atom of boron, we could look at the periodic table to find the element symbol of boron. But luckily for us, we know it already. Specifically, we know that this atom is also an atom of boron because, once again, we’ve been told that the nuclear decay equation shows neutron emission by boron-18. So whatever is on the left-hand side must be boron-18. And, hence, we know that the element boron will have an element symbol B.
Which means that all that’s happening here is that an atom of boron-18 — which, in other words, means five protons and 18 minus five neutrons or 30 neutrons — is turning into a boron-17 atom with one fewer neutrons. It’s now got 12 neutrons and still five protons because it’s still boron. And the neutron that is lost from the boron nucleus is the neutron that’s released.
And so, at this point, we’ve answered both our questions. The name of element X is boron. And the element symbol that should replace X in the nuclear equation is B.