Question #1ef85

The first thing that you have to do in order to write the electron configuration of an atom using noble gas shorthand notation is to identify the noble gas that comes immediately before your atom in the periodic table.

Once you do that, you use the electron configuration of that noble gas to replace the part that's identical for your atom.

• Boron, #B#

Boron is located in group 13, period 2 of the periodic table and has an atomic number equal to 5. This means that its electron configuration must account for 5 electrons.

#"B": 1s^(2) 2s^(2) 2p^(1)#

The noble gas that comes before boron in the periodic table is helium, #He#, which has 2 electrons that surround its nucleus.

#"He": 1s^(2)#

This means that boron's noble gas shorthand notation will be

#"B": underbrace(1s^(2))_(color(blue)("[He]")) 2s^(2) 2p^(1) = ["He"] 2s^(2) 2p^(1)#

• Neptunium, #Np#

Neptunium has an atomic number equal to 93, which means that its electron configuration must account for 93 electrons. The noble gas that comes before neptunium in the periodic table is radon, #Rn#, which has 86 electrons surrounding its nucleus.

If radon's electron configuration accounts for 86 electrons, you only have to add 7 electrons outside of the noble gas core to get neptunium's configuration.

#"Np": underbrace(1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(10) 4s^(2) 4p^(6) 4d^(10) 5s^(2) 5p^(6) 4f^(14) 5d^(10) 6s^(2) 6p^(6))_(color(blue)("[Rn]")) " "5f^(4) 6d^(1) 7s^(2)#

Therefore, the noble gas shorthand notation of neptunium is

#"Np": ["Rn"] 5f^(4) 6d^(1) 7s^(2)#