Question

For each element, indicate the number of valence electrons, core electrons, and unpaired electrons in the ground state: (a) nitrogen, (b) silicon, (c) chlorine.

Short answer

(a) Nitrogen: 5 valence electrons, 2 core electrons, and 3 unpaired electrons. (b) Silicon: 4 valence electrons, 10 core electrons, and 2 unpaired electrons. (c) Chlorine: 7 valence electrons, 10 core electrons, and 1 unpaired electron.

Step-by-step solution

(a) Nitrogen

1. Electron configuration: Nitrogen has 7 electrons. Its electron configuration is: \( 1s^2 2s^2 2p^3 \) 2. Valence electrons: The outermost shell is the second shell, with 2s and 2p orbitals. There are 5 valence electrons (2 from 2s and 3 from 2p). 3. Core electrons: The first shell has 2 electrons in the 1s orbital. There are 2 core electrons. 4. Unpaired electrons: The 2p orbital has 3 unpaired electrons.

(b) Silicon

1. Electron configuration: Silicon has 14 electrons. Its electron configuration is: \( 1s^2 2s^2 2p^6 3s^2 3p^2 \) 2. Valence electrons: The outermost shell is the third shell, with 3s and 3p orbitals. There are 4 valence electrons (2 from 3s and 2 from 3p). 3. Core electrons: The first and second shells have a total of 10 electrons. There are 10 core electrons. 4. Unpaired electrons: The 3p orbital has 2 unpaired electrons.

(c) Chlorine

1. Electron configuration: Chlorine has 17 electrons. Its electron configuration is: \( 1s^2 2s^2 2p^6 3s^2 3p^5 \) 2. Valence electrons: The outermost shell is the third shell, with 3s and 3p orbitals. There are 7 valence electrons (2 from 3s and 5 from 3p). 3. Core electrons: The first and second shells have a total of 10 electrons. There are 10 core electrons. 4. Unpaired electrons: The 3p orbital has 1 unpaired electron.

Key concepts

Electron Configuration

Understanding the electron configuration of an atom is crucial for predicting its chemical behavior. The electron configuration is a representation of the arrangement of an atom's electrons in its orbitals. Electrons occupy orbitals starting from the lowest energy level moving towards higher ones.

Take nitrogen as an example. Its electron configuration is given by the notation \( 1s^2 2s^2 2p^3 \), signifying that in the first energy level (1s), it has 2 electrons. Subsequently, the second energy level is populated with 2 electrons in the 2s orbital and 3 electrons in the 2p orbitals. This filling order adheres to the aufbau principle, which illustrates how electrons fill the orbitals based on increasing energy levels.

Core Electrons

Distinguishing between core and valence electrons is important when it comes to chemical bonding. Core electrons are those found in the inner shells of an atom; they are not involved in chemical bonding. Instead, they shield the positive charge of the nucleus from the valence electrons.

Using silicon as an example, we can say it has 10 core electrons. These are located in the 1s, 2s, and 2p orbitals (\( 1s^2 2s^2 2p^6 \)). These electrons are closer to the nucleus and thus are held more tightly, differentiating them from the valence electrons in the outermost orbitals.

Unpaired Electrons

The presence of unpaired electrons can have a profound effect on the magnetic and chemical properties of an atom. Unpaired electrons are electrons in an atom's orbitals that do not have a partner with opposite spin. This lone status often makes them responsible for the atom's chemical reactivity.

For instance, in chlorine, the electron configuration (\( 1s^2 2s^2 2p^6 3s^2 3p^5 \) shows that there are 5 electrons in the 3p orbitals; however, since these orbitals can hold a maximum of 6 electrons, one of them remains unpaired. It is this unpaired electron that contributes to chlorine's high reactivity.

Ground State

The ground state of an atom represents its most stable, lowest energy configuration. Electrons are arranged in the lowest available energy levels, following the rules outlined by quantum mechanics. In ground state, nitrogen, silicon, and chlorine all have their electrons arranged in such a way that their net energy is minimized.

When electrons are excited, either by heat or light, they can move to higher energy levels, but when they return to lower levels, the atom is said to be in its ground state. During these transitions, the atom may emit energy in the form of light, which is observable in spectroscopy. Ground state electron configurations serve as a reference point for understanding an atom’s behavior during chemical reactions.