You have to check each statement, so this is equivalent to 5 different questions.
Answers:
The true statements are:
b. Si has valence electrons in the n = 3 energy level.d. Xe has valence electrons in the n = 5 energy level.
Explanations:
a. Li has valence electrons in the n = 1 energy level.
False.
Valence electrons are the electrons in the outermost main energy level (shell of electrons).
To determine where the valence electrons are, you build the electron configuration, using Aufbau rules to predict the orbital filling: in increasing order of energy.
The atomic number of lithium (Li) is 3. Hence, you have to distribute 3 electrons, and so its electron confiuration is:
1s² 2s¹
The only valence electron is in the 2s orbital, i.e. in the n = 2 energy level.
b. Si has valence electrons in the n = 3 energy level.
True
Silicon (Si) has atomic number 14, so you have to distribute 14 electrons in increasing order of energy:
1s² 2s² 2p⁶ 3s² 3p²
Thus, Si has five valence electrons, and they are in the n = 3 energy level.
c. Ga has valence electrons in the n = 3 energy level.
False
Gallium has atomic number 31, so you have to distribute 31 electrons, filling the orbitals in increasing order of enery.
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p¹
The highest energy level is 4. This is where the valence electrons are. So, Ga has the valence electrons in the n = 4 level (not n = 3 as the statement describes).
d. Xe has valence electrons in the n = 5 energy level.
True
The atomic number of Xe is 54.
Using the short notation (noble gas notation), and filling the orbitals in increasing order of energy, you get the configuration:
[Kr] 5s² 4d¹⁰ 5p⁶.
Hence, the valence electrons are in the n ) 5 level, such as the statement describes.
e. P has valence electrons in the n = 2 energy level.
False
Phosphorus (P) has atomic number 15, hence there are 15 electrons.
The electron configuration following the increasing order of energy, which you can remember using Aufbau rules, is:
1s² 2s² 3s² 3p³
Then, the valence electrons are in the n = 3 energy level; not in the n = 2 energy level.
