Question #6706a

2 Answers
Aug 31, 2017

Answer:

#n=4, l=0, m=0, s=1/2#

Explanation:

For Chromium,

#Z=24#

Electronic configuration

#1s^2,2s^2,2p^6,3s^2,3p^6,3d^5,4s^1#

So, for the last electron,

#n=4#

#l=0#

#m=0#

#s=1/2#

Aug 31, 2017

Answer:

The quantum numbers are #n = 3, l = 2, m_l = "+2", m_s = "+½"#.

Explanation:

Chromium has atomic number 24.

You can write its electron configuration as

#"[Cr] 1s"^2 color(white)(l)"2s"^2 "2p"^6 color(white)(l)"3s"^2 "3p"^6color(white)(l) "4s" color(white)(l)"3d"^5# or

#"[Cr] 1s"^2color(white)(l) "2s"^2 "2p"^6color(white)(l) "3s"^2 "3p"^6 "3d"^5color(white)(l)"4s"#

However you write it, you must remember that the #"3d"# orbitals have the highest energy and are filled last in the Aufbau process.

images.tutorvista.com

The quantum numbers of the first five #"3d"# electrons are

#bbul(ncolor(white)(m)lcolor(white)(m)m_lcolor(white)(m)m_s)#
#3color(white)(m)2color(white)(ml)"-2"color(white)(m)"+½"#
#3color(white)(m)2color(white)(ml)"-1"color(white)(m)"+½"#
#3color(white)(m)2color(white)(mll)0color(white)(m)"+½"#
#3color(white)(m)2color(white)(m)"+1"color(white)(m)"+½"#
#color(red)(3color(white)(m)2color(white)(m)"+2"color(white)(m)"+½")#

Thus, the quantum numbers of the last electron added to chromium are

#3, 2, "+2, +½"#.