Which of the following species are isoelectronic? Select all that apply.
1) S^2-
2) Be^2+
3) Cl^-
4) K^+
5) Ca^2+
6) Se^2-
Isoelectronic means the same number of electrons.
I would suggest you write out the electron configuration of each, then compare. For example, #1 is
16S = 1s2 2s2 2p6 3s2 3p4; therefore,
take away two outside electrons and
16S^-2 becomes 1s2 2s2 2p6 3s2 3p2
etc.
For S^2- why are taking away electrons? Are suppose to add electrons?
So far I have S^2-, Cl^-, K^+, and Ca^2+ instead the other two as the answer. Please tell me if I have these answers correct.
To determine which species are isoelectronic, we need to compare the number of electrons in their outermost energy level or valence shell. Isoelectronic species have the same number of electrons.
Let's analyze each option and determine their number of electrons:
1) S^2-
To find the number of electrons for an ion, we need to subtract the charge from the number of electrons in the neutral atom. Sulfur (S) has an atomic number of 16, so it has 16 electrons. The charge is 2-, so we need to add 2 electrons to neutral sulfur, giving us a total of 18 electrons.
2) Be^2+
Beryllium (Be) has an atomic number of 4, which means it has 4 electrons. The charge is 2+, so we need to subtract 2 electrons from neutral beryllium, giving us a total of 2 electrons.
3) Cl^-
Chlorine (Cl) has an atomic number of 17, so it has 17 electrons. The charge is 1-, so we need to add 1 electron to neutral chlorine, giving us a total of 18 electrons.
4) K^+
Potassium (K) has an atomic number of 19, so it has 19 electrons. The charge is 1+, so we need to subtract 1 electron from neutral potassium, giving us a total of 18 electrons.
5) Ca^2+
Calcium (Ca) has an atomic number of 20, so it has 20 electrons. The charge is 2+, so we need to subtract 2 electrons from neutral calcium, giving us a total of 18 electrons.
6) Se^2-
Selenium (Se) has an atomic number of 34, so it has 34 electrons. The charge is 2-, so we need to add 2 electrons to neutral selenium, giving us a total of 36 electrons.
After determining the number of electrons for each species, we can see that options 1), 3), 4), 5), and 6) all have 18 electrons, making them isoelectronic. Therefore, the correct options are:
1) S^2-
3) Cl^-
4) K^+
5) Ca^2+
6) Se^2