neutrons. Different atoms of the same element may vary
as to the number of neutrons they contain. That’s what
makes them isotopes.
Both statements are true. Now see if this sentence
makes sense: “The periodic table does not report mass
numbers because a mass number can be assigned to one
isotope of an element but not to an element in general.”
It does, so fill in the oval marked CE.
- F, T Divide and conquer. Look at the first statement on its own, and
decide whether it’s true or false. Electrons are negatively charged, so
if we add an electron to an atom, it becomes a negatively charged ion.
This statement is false. Now look at the second statement; is it true?
Yes. Electrons are negatively charged. The first statement is false, and
the second is true. Do not fill in the CE oval.
- E You know the answer, so don’t fall into the camouflage trap. The
atomic number represents the number of protons in the nucleus, and it gives
the atom its identity. Any sodium atom or ion must have, in its nucleus, the
same number of protons as any other sodium atom; otherwise it isn’t
sodium. Both (A) and (B) are wrong because sodium ions can carry
different charges, depending on how many electrons they’ve gained or lost.
(C) and (D) are wrong because different isotopes of sodium will differ in
the number of neutrons in the nucleus. That means their mass number will
differ. But all sodium atoms or ions must have 11 protons in their nuclei.
That’s why (E) is correct.
- A You know what isotopes are—atoms of the same element that differ
in their number of neutrons. Isotopes may also differ in their number of
electrons. They must differ in their mass numbers since they have different
numbers of neutrons. They can’t differ in their number of protons, or they
wouldn’t be atoms of the same element. (B), (C), (D), and (E) are incorrect,
and (A) is correct.
