# What ion/atom/isotope has 24 neutrons and 20 electrons?

Doing chem homework, having a hard time.

Relevance

Ooh, this is a tricky one. Have a periodic table handy.

Since we don't know whether it's an ion or a neutral atom, let's write down some possibilities:

-4 ion, -3 ion, -2 ion, -1 ion, neutral atom, +1 ion, +2 ion, +3 ion, +4 ion

We know we have 20 electrons, so for each of these possibilities, we can determine the number of protons, and from that, the name of the atom or ion:

-4 ion, -3 ion, -2 ion, -1 ion, neutral atom, +1 ion, +2 ion, +3 ion, +4 ion

16 p+, 17 p+, 18 p+, 19 p+, 20 p+, 21 p+, 22 p+, 23 p+, 24 p+

S(4-), Cl(3-), Ar(2-), K(1-), Ca, Sc(1+), Ti(2+), V(3+), Cr(4+)

We also know we have 24 neutrons, so for each of these possibilities, we can determine the mass number (A) for each possibility, and from that, determine the possible isotopes:

-4 ion, -3 ion, -2 ion, -1 ion, neutral atom, +1 ion, +2 ion, +3 ion, +4 ion

16 p+, 17 p+, 18 p+, 19 p+, 20 p+, 21 p+, 22 p+, 23 p+, 24 p+

S(4-), Cl(3-), Ar(2-), K(1-), Ca, Sc(1+), Ti(2+), V(3+), Cr(4+)

A=40, A=41, A=42, A=43, A=44, A=45, A=46, A=47, A=48

S-40(4-), Cl-41(3-), Ar-42(2-), K-43(1-), Ca-44, Sc-45(1+), Ti-46(2+), V-47(3+), Cr-48(4+)

Now check our periodic table to see if any of these possibilities is a stable isotope. S-40, Cl-41, Ar-42, K-43, V-47, and Cr-48 are not stable isotopes, so we can narrow our possibilities down to:

Ca-44, Sc-45(1+), Ti-46(2+)

Finally, check oxidation states. Scandium is usually in the +3 oxidation state. Titanium is usually in the +4 oxidation state. Therefore the calcium-44 isotope, in the neutral metallic state, is the most likely answer.

• Login to reply the answers
• Scandium, Sc+, one electron taken from it, i think

• Login to reply the answers