Question

for each of the following elements, provide the correct electron configuration and the valence electron count: 5. h: 6. ar: 7. si: 8. cr: 9. k: 10. br:

Explanation:

Step1: Determine electron - configuration rules

Electrons fill orbitals in order of increasing energy (1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p etc.). The s - orbital can hold 2 electrons, p - orbital 6 electrons, d - orbital 10 electrons and f - orbital 14 electrons. Valence electrons are the electrons in the outermost shell.

Step2: H (Hydrogen)

Hydrogen has 1 electron. Its electron - configuration is $1s^1$. The number of valence electrons is 1.

Step3: Ar (Argon)

Argon has 18 electrons. Its electron - configuration is $1s^22s^22p^63s^23p^6$. The number of valence electrons is 8.

Step4: Si (Silicon)

Silicon has 14 electrons. Its electron - configuration is $1s^22s^22p^63s^23p^2$. The number of valence electrons is 4.

Step5: Cr (Chromium)

Chromium has 24 electrons. Due to the stability of half - filled d - orbitals, its electron - configuration is $1s^22s^22p^63s^23p^64s^13d^5$ instead of the expected $1s^22s^22p^63s^23p^64s^23d^4$. The number of valence electrons is 6.

Step6: K (Potassium)

Potassium has 19 electrons. Its electron - configuration is $1s^22s^22p^63s^23p^64s^1$. The number of valence electrons is 1.

Step7: Br (Bromine)

Bromine has 35 electrons. Its electron - configuration is $1s^22s^22p^63s^23p^64s^23d^{10}4p^5$. The number of valence electrons is 7.

Answer:

1. Electron - configuration: $1s^1$, Valence electrons: 1
2. Electron - configuration: $1s^22s^22p^63s^23p^6$, Valence electrons: 8
3. Electron - configuration: $1s^22s^22p^63s^23p^2$, Valence electrons: 4
4. Electron - configuration: $1s^22s^22p^63s^23p^64s^13d^5$, Valence electrons: 6
5. Electron - configuration: $1s^22s^22p^63s^23p^64s^1$, Valence electrons: 1
6. Electron - configuration: $1s^22s^22p^63s^23p^64s^23d^{10}4p^5$, Valence electrons: 7