Question

*remember: isoelectronic means the same # of electrons, which also means identical electron configuration!

1. **which ion is isoelectronic to mg⁺²?

a. ca⁺² b. cl⁻¹ c. na⁺¹ d. s⁻²

1. **which pair has identical electron configurations?

a. s⁻² and cl⁻¹ c. k⁰ and na⁺¹
b. s⁰ and ar⁰ d. cl⁻¹ and k⁰

1. *how do you know?
2. *why might it be important to identify isoelectronic ions/atoms?

for each of the following atoms, write the full electron configuration.

1. selenium atom 2. selenium ion with a charge of +4
2. fluorine atom 4. fluoride ion with a charge of -1
3. silver atom 6. silver ion with a charge of +1

Explanation:

1. Which ion is isoelectronic to \(Mg^{+2}\)?

• Step 1: Determine the number of electrons in \(Mg^{+2}\)

The atomic number of \(Mg\) is \(12\). For \(Mg^{+2}\), the number of electrons \(=12 - 2=10\)

• Step 2: Calculate the number of electrons for each option
• For \(Ca^{+2}\): Atomic number of \(Ca\) is \(20\). Number of electrons \(=20 - 2 = 18\)
• For \(Cl^{-1}\): Atomic number of \(Cl\) is \(17\). Number of electrons \(=17+1 = 18\)
• For \(Na^{+1}\): Atomic number of \(Na\) is \(11\). Number of electrons \(=11 - 1=10\)
• For \(S^{-2}\): Atomic number of \(S\) is \(16\). Number of electrons \(=16 + 2=18\)

2. Which pair has identical electron configurations?

• Step 1: Determine the electron - configuration for each species
• For \(S^{-2}\): Atomic number of \(S\) is \(16\). \(S^{-2}\) has \(16 + 2=18\) electrons. Electron - configuration: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}\)
• For \(Cl^{-1}\): Atomic number of \(Cl\) is \(17\). \(Cl^{-1}\) has \(17+1 = 18\) electrons. Electron - configuration: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}\)
• For \(K^{0}\): Atomic number of \(K\) is \(19\). Electron - configuration: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}\)
• For \(Na^{+1}\): Atomic number of \(Na\) is \(11\). \(Na^{+1}\) has \(11 - 1 = 10\) electrons. Electron - configuration: \(1s^{2}2s^{2}2p^{6}\)
• For \(S^{0}\): Atomic number of \(S\) is \(16\). Electron - configuration: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{4}\)
• For \(Ar^{0}\): Atomic number of \(Ar\) is \(18\). Electron - configuration: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}\)

3. How do you know?

• For isoelectronic species (question 1), we calculate the number of electrons for the given ion (\(Mg^{+2}\)) and for each of the options. Two species are isoelectronic if they have the same number of electrons.
• For identical electron - configurations (question 2), we write out the full electron - configuration (using the Aufbau principle: filling electrons in the order \(1s<2s<2p<3s<3p<4s<3d\) etc.) for each species in the pair. If the sequence of filled orbitals is the same, they have identical electron configurations

4. Why might it be important to identify isoelectronic ions/atoms?

Answer:

s:

1. Question 1: \(c. Na^{+1}\)
2. Question 2: \(a. S^{-2}\) and \(Cl^{-1}\)