Chemistry 121
Mines
Answers: Orbitals and Electron Configurations Practice
1. (50) Write full electron configurations for each of the following elements.
2
2
3
2
2
6
(a) N: 1s 2s 2p
2
(b) S: 1s 2s 2p 3s 3p
4
2. (52) Write full orbital diagrams for each of the following elements and indicate the
number of unpaired electrons in each.
(a) B: ___ ___ ___ ___ ___
1s
2s
2p
(b) N: ___ ___ ___ ___ ___
1s
one unpaired electron
2s
three unpaired electrons
2p
3. (58) Write full (ground state) electron configurations for each of the following elements
and indicate the valence electrons and the core electrons.
(a) Sr: 1s22s22p63s23p64s23d104p65s2
The two electrons in the 5s orbital are the valence electrons. All others (the
remaining 36) are core electrons.
(b) Cl: 1s22s22p63s23p5
The two 3s electrons and the five 3p electrons are the valence electrons. The
remaining 10 electrons are core electrons.
4. (62) How many valence electrons are in each of the following:
(a) Ba: 2 (s2 outer electron configuration)
(b) Al: 3 (s2p1 outer electron configuration)
2
(c) Be: 2 (s outer electron configuration)
(d) Se: 6 (s2p4 outer electron configuration) [NOTE: The 10 d electrons in the fourth
period are part of the third energy level, not the fourth, so they are core
electrons, not valence ones.]
5. (64) Give the outer electron configuration for each of the following columns in the
periodic table (assume ground state atoms):
2 1
(a) 3A: s p
(b) 4A: s2p2
2 4
(c) 6A: s p
(d) 8A: s2p6
6. (68) Use the periodic table to write electron configurations for each of the following
elements (assume ground states):
(a) Se: 1s22s22p63s23p64s23d104p4
(b) Sn: 1s22s22p63s23p64s23d104p65s24d105p2
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Answer Key, Orbitals and Electron Configurations Practice
7. (74) Name an element in the fourth period of the periodic table with:
(a) 5 valence electrons: As (arsenic)
(b) a total of 4 4p electrons: Se (selenium)
(c) a total of 3 3d electrons: V (vanadium)
8. (94) Write electron configurations for any excited state of an atom of each of the
following.
(a) F: 1s22s22p5 would be the ground state configuration, so an excited state would be
anything with the same number of electrons that is not the ground state configuration!
Specifically, at least one electron must be higher in energy than it "could" be (in the
ground state). E.g.:
1s22s12p6; 1s22s22p43s1; 1s02s22p63s1;
1s22s12p55s1, 1s22s12p59s1 etc.
(b) Sc: 1s22s22p63s23p64s23d1 is the ground state configuration, so some excited states
are:
1s22s22p63s23p64s13d2; 1s22s22p63s23p64s24p1; 1s22s12p63s23p64s23d15s1, etc.
As you can see, there are an infinite number of exited states possible for any atom
because there are an infinite number of energy levels!
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