Question

30 using a periodic table, write the full electron configuration of bromine (br) so that all the subshells in each principal energy shell are grouped together. go online for more practice problems.

Explanation:

Step1: Determine bromine's atomic number

Bromine (Br) has an atomic number of 35, which means it has 35 electrons.

Step2: Fill electron - subshells

We fill the subshells in the order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p.

• 1s can hold 2 electrons: $1s^{2}$.
• 2s can hold 2 electrons: $2s^{2}$.
• 2p can hold 6 electrons: $2p^{6}$.
• 3s can hold 2 electrons: $3s^{2}$.
• 3p can hold 6 electrons: $3p^{6}$.
• 4s can hold 2 electrons: $4s^{2}$.
• 3d can hold 10 electrons: $3d^{10}$.
• After filling the above sub - shells, we have used $2 + 2+6 + 2+6 + 2+10=30$ electrons. We need to place the remaining $35 - 30 = 5$ electrons in the 4p sub - shell: $4p^{5}$.

Step3: Group subshells by principal energy shell

The full electron configuration grouped by principal energy shell is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{5}$.

Answer:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{5}$