Question

Select all that apply.

Any element can always be identified by its _____.

atomic mass
number of neutrons
number of protons
atomic number

Answer 1

#protons

Answer 2

To answer this, let's consider the periodic table and some of the trends which exist within it. Remember that for every element on the table, the following values are defined:

-Atomic Number: The number of protons in the nucleus of an atom of the element. For any neutral atom, the number of the positively charged protons must be 'balanced' out by negatively charged electrons orbiting the nucleus, so the atomic number also tells us the number of these present.
-Atomic Mass: The number of protons + the number of neutrons existing within the nucleus of an atom of a particular element. On the periodic table, the atomic mass of an element is defined as a weighted average of the masses of all the element's isotopes based on their natural abundance (hence the decimal point figures). It follows that:

The number of neutrons in the nucleus of any particular atom of an element= Atomic Mass (No. of protons + neutrons) - Atomic Number (No. of protons)

As we go along a row (period) from left to right, we see that:
-The atomic number is increasing by 1 on each occasion for each element, and
-The atomic mass is also generally increasing, but there is no defined, repeating pattern to its general increase across the row. This is because whilst the number of protons is increasing by 1 on each occasion, the number of neutrons present is not always increasing to the same strict pattern.

Whilst we can't use the atomic mass or the number of neutrons present to formally identify an element, we can use the number of protons present (i.e. the atomic number), as this is a fixed value for all atoms of a given element which never changes. It is essentially the element's 'fingerprint' which we can use to identify it with (i.e. an atom with 1 proton must be hydrogen).

So, I would say that the no. of protons or atomic number are acceptable answers here, as they are essentially both talking about the same thing.

Answer 3

Cheers mate. Helps a lot. :D

Answer 4

Atomic mass