Question

periodic table. the atomic number of an element is 15. what is the likely arrangement of the valence and core electrons in a neutral atom of this element? a. there are 3 valence electrons and 12 core electrons. b. there are 4 valence electrons and 11 core electrons. c. there are 5 valence electrons and 10 core electrons. d. there are 6 valence electrons and 9 core electrons.

Explanation:

Step1: Recall electron - configuration concept

The atomic number of an element is equal to the number of electrons in a neutral atom. For an element with atomic number \(Z = 15\), the electron - configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}\).

Step2: Distinguish between core and valence electrons

Core electrons are the electrons in the inner shells, and valence electrons are in the outermost shell. The first - two shells (\(n = 1\) and \(n=2\)) are filled: \(1s^{2}2s^{2}2p^{6}\), which gives \(2 + 2+6=10\) core electrons. The electrons in the \(n = 3\) shell (\(3s^{2}3p^{3}\)) are valence electrons, and there are \(2 + 3=5\) valence electrons.

Answer:

C. There are 5 valence electrons and 10 core electrons.