Question

activity a: isotope notation get the gizmo ready: set protons to 2 and neutrons to 2. check that show isotope notation is selected. question: how are isotopes written down? 1. explore: below the helium atom you see the isotope notation for helium - 4. add and subtract protons and neutrons a few times using the arrow buttons. notice how the isotope notation changes when you do this. a. what does the top number equal? b. which particle determines the atomic number? d. what percentage of the element consists of this isotope?

Explanation:

Step1: Recall isotope notation concept

In isotope notation, the top - number is the mass number. The mass number ($A$) of an atom is the sum of the number of protons ($p$) and neutrons ($n$). Given protons = 2 and neutrons = 2, then $A=p + n$.

Step2: Calculate the mass number

$A=2 + 2=4$. The atomic number ($Z$) of an element is determined by the number of protons.

Answer:

A. 4
B. Protons