Question

1. the valence electrons in an atom of phosphorus in the ground state are all found in the a) first shell b) second shell c) third shell d) fourth shell 3. what is the total number of valence electrons in an atom of selenium in the ground state? a) 8 b) 16 c) 2 d) 6 5) an atom of chlorine and an atom of bromine have the same a) electronegativity b) ionization energy c) atomic radius d) number of valence electrons

Explanation:

1. Phosphorus has an atomic number of 15. Its electron configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}\). Valence electrons are in the outermost shell. Here, the outermost shell is the third shell (\(n = 3\)).
2. Selenium has an atomic number of 34. Its electron configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{4}\). The valence - shell is \(n=4\) and the number of valence electrons is \(2 + 4=6\) (from \(4s^{2}\) and \(4p^{4}\)).
3. Chlorine (\(Cl\), atomic number 17) has an electron configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}\) and bromine (\(Br\), atomic number 35) has an electron configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{5}\). Both are in group 17 (halogens) and have 7 valence electrons. Electron - negativity, ionization energy, and atomic radius differ due to differences in atomic size and nuclear charge.

Answer:

1. C. third shell
2. D. 6
3. D. number of valence electrons