1.) How many unpaired electrons are there in the Fe3+ ion when it is in its ground state?

2.) Which of these ions have noble gas electron configurations? (Give the electron configuration of each ion.)

Cr3+
Al3+
Se2−

3.) Which of the following sets of species is/are isoelectronic?

S2−, Cl−, K+
Na+, Mg2+, Al3+
Na+, K+, Li+

For any that are isoelectronic, put them in order of increasing radius.

4.) Using the Periodic Table classify each of these elements as a metal, nonmetal, or metalloid. Does the element form an ion? If so, what will the charge of the ion be?

Pb
K
Xe
Al
I (iodine)

⇒The electron configuration for the Fe3+ ion is 1s2 2s2 2p6 3s2 3p6 3d5. ⇒The positive charge of three in this ion shows that the atom lost three electrons.

⇒Electrons are taken from the outermost electron shell first, eliminating the two in the 4s sublevel. The other lost electron is then taken from the 3d sublevel.

⇒d subshell can occupy 10 electrons (in 5 orbitals). Pairing of electrons take place only after each orbital is singly occupied (Hund’s rule).

⇒ So, there are 5 electrons in the d subshell. So, each d orbital is singly occupied (unpaired).

⇒ This means there are 5 unpaired electrons in Fe3+

2) noble gas configuration means they have 8 electrons on the the outer shell.

⇒Cr3+ : Cr has 24 electrons of which 1 electron on the outer shell, so Cr3+ is not in the noble gass electron configuration

⇒1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 0 3 d 3

⇒Note that it is 4 s 1 3 d 5 and not 4 s 2 3 d 4 because a half filled d orbital is more stable than a partially filled d orbital.

⇒Al3+: Al has 13 electrons, of which 3 are on the outer shell. Al3+ has 3electrons less, this means it loses the 3 electrons on the outer shell. So Al3+ has 10 electrons, of which 8 on the outer shell. This means it's in the noble gas electron configuration.

⇒The electron configuration of an aluminum ion, Al3+, is 1s2, 2s2, 2p6

⇒Se2-: Se has 34 electrons, of which 6 are on the outer shell. Se2- has 2 electrons more, this means it gains 2 electrons on the outer shell. So Se2- has 36 electrons, of which 8 on the outer shell. This means it's in the noble gas electron configuration.

⇒1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 10 4 s 2 4 p 6

3) Isoelectronic species means those species which have same no. of total electrons :

S2-, Cl-,K+ :

⇒S has 16 electrons, S2- has 2 electrons more so 18 electrons

⇒Cl has 17 electrons,Cl- has 1 electron more so 18 electrons

⇒K has 19 electrons, K+ has 1 electron less so 18 electrons

⇔This is an isoelectronic set because they all have 18 electrons

⇔in order of increasing radius : S2- > Cl- > Al3+ : because in Sé- are the most electrons added.

Na+,Mg2+,Al3+

⇒Na has 11 electrons, Na+ has 1 electron less so 10 electrons

⇒Mg has 12 electrons, Mg2+ has 2 electrons less so 10 electrons

⇒Al has 13 electrons, Al3+ has 3 electrons less so 10 electrons

⇔This is an isoelectronic set because they all have 10 electrons

⇔in order of increasing radius : Na+ >Mg2+ > Al3+ : because in Sé- are the most electrons added.

Na+,K+,Li+

⇒Na has 11 electrons, Na+ has 1 electron less so 10 electrons

⇒K has 19 electrons, K+ has 1 electron less so 18 electrons

⇒Li has 3 electrons, Li+ has 1 electron less so 2 electrons

⇔This is no isoelectronic set

4) ⇒Pb is a metal. It's part of the p-block and the carbon group. It forms a Pb-ion ( Pb2+)

⇒ K is an alkalimetal ( so part of the metals). It forms K-ion (K+)

⇒ Xe is a nonmetal and part of the noble gasses. It doesn't form an ion, because it has 8 electrons on the outer shell, why it's stable.

⇒Al is a metal. It forms an Al3+ ion

⇒Iodine is a halogene., so a nonmetal. It forms I-, ion