Strike a nucleus and its contents can change: a particle added, a particle knocked out. Afterward, one count decides what atom remains.
From earlier science you know that the number of protons fixes which element an atom is. This lesson turns the fact into a quick sort you can run on any nucleus change.
Here is a carbon nucleus: six protons and six neutrons.
The carbon nucleus gains one neutron, so it now holds six protons and seven neutrons.
Is it still carbon? Yes: the proton count has not changed, so it is the same element.
Now the same nucleus loses one proton instead, leaving five protons and seven neutrons.
Is it still carbon? No: the proton count has changed, so it is a different element.
Change the neutron count, and the element stays the same.
Change the proton count, and the element changes.
Gaining or losing makes no difference to the sort; only the proton count matters.
An aluminum nucleus gains one neutron. Is the result the same element or a different element?
The sort looks only at the proton count.
Gaining a neutron leaves the proton count unchanged.
The proton count alone fixes the element.
The same element: the nucleus is still aluminum.
The same aluminum nucleus now loses one proton. Is the result the same element or a different element?
The sort looks only at the proton count.
Losing a proton changes the proton count.
A changed proton count means a changed element.
A different element: the nucleus is no longer aluminum.
A nitrogen nucleus gains one neutron. Is the result the same element or a different element?
An oxygen nucleus loses one proton. Is the result the same element or a different element?
A helium nucleus gains one proton. Is the result the same element or a different element?
A lithium nucleus loses one neutron. Is the result the same element or a different element?
A fluorine nucleus gains two neutrons. Is the result the same element or a different element?
A neon nucleus loses one proton. Is the result the same element or a different element?
Which change turns a sodium nucleus into the nucleus of a different element?
A zinc nucleus gains one neutron, and the atom is still zinc. Which count fixes the element?
An oxygen nucleus holds 8 protons and 8 neutrons, and then one change happens to it. Which result shows it became a different element?