Detailed explanation of AP Chemistry Question of the Day is posted on YouTube. Check it out. The link is https://youtu.be/ihBBlbooU-E
All the best!
Ling
Wednesday, February 5, 2020
Tuesday, February 4, 2020
AP Chemistry Question of the Day --69
I was reviewing atomic structure with my students and find the following question confusing to quite some people and I decided to share it here.
Which of the following transition metal ions has the most unpaired electrons?
A. Co (2+)
B. Mn (2+)
C. Zn (2+)
D. Fe (2+)
The answer is B. For transition metals electrons fills in the 4s subshell first before they fill the 3d subshell due to Aufbau Rule which states that electrons fill in orbital with lower energy first. Since 4s has lower energy than 3d, they fill in 4s first. There are 5 orbitals in 3d subshell, according to Hund's Rule, which state that electrons will fill separate orbitals before they pair up to avoid repulsions, as a result, Co has 7 electrons in 3d, 3 unpaired and 4 paired up, Mn has 5 unpaired in 3d, Zn has no unpaired in 3d and Fe has 4 unpaired and 2 paired electrons in 3d.
Now comes the tricky part, when transition metals form cations, they always lose their outmost electrons first. As a result, the 4s electrons are lost and the number of electrons remain the same as the original atoms if the charge of the ions are +2. Only when you are losing more than 2, addition electrons in 3d will be removed.
Hope this is helpful to you.
All the best!
Ling
Which of the following transition metal ions has the most unpaired electrons?
A. Co (2+)
B. Mn (2+)
C. Zn (2+)
D. Fe (2+)
The answer is B. For transition metals electrons fills in the 4s subshell first before they fill the 3d subshell due to Aufbau Rule which states that electrons fill in orbital with lower energy first. Since 4s has lower energy than 3d, they fill in 4s first. There are 5 orbitals in 3d subshell, according to Hund's Rule, which state that electrons will fill separate orbitals before they pair up to avoid repulsions, as a result, Co has 7 electrons in 3d, 3 unpaired and 4 paired up, Mn has 5 unpaired in 3d, Zn has no unpaired in 3d and Fe has 4 unpaired and 2 paired electrons in 3d.
Now comes the tricky part, when transition metals form cations, they always lose their outmost electrons first. As a result, the 4s electrons are lost and the number of electrons remain the same as the original atoms if the charge of the ions are +2. Only when you are losing more than 2, addition electrons in 3d will be removed.
Hope this is helpful to you.
All the best!
Ling
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