Question

A chlorine atom in its ground state has a total of seven electrons in orbitals related to the atom’s third energy level. How many of the seven electrons occupy p orbitals? How many of the 17 electrons in a chlorine atom occupy p orbitals?

Short answer

In a chlorine atom, there are 5 electrons in the p orbitals of the 3rd energy level in its ground state, and a total of 11 electrons occupy p orbitals throughout the entire atom.

Step-by-step solution

Understand the electron configuration of a chlorine atom

To find the number of electrons in the p orbitals in a chlorine atom, we first need to know the electron configuration of a chlorine atom. Chlorine has a total of 17 electrons and its electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^5\).

Identify the p orbitals in the 3rd energy level

In the electron configuration, the value of the principal quantum number, n, indicates the energy level. In the case of chlorine, we are interested in the 3rd energy level (n=3). The 3rd energy level orbitals are represented by \(3s^2 3p^5\). Among these, the p orbitals are represented by the term \(3p^5\), which indicates that there are 5 electrons in the 3p orbitals.

Determine the total number of electrons in the p orbitals

Now that we have found the number of electrons in the p orbitals of the 3rd energy level, we need to find the total number of electrons in the p orbitals. To do this, we need to consider the p orbitals in all energy levels. From the electron configuration, we can see that there are 6 electrons in the 2p orbitals (\(2p^6\)) in addition to the 5 electrons in the 3p orbitals (\(3p^5\)). Therefore, the total number of electrons in the p orbitals for a chlorine atom is 6 + 5 = 11 electrons. Answer: There are 5 electrons in the p orbitals of the 3rd energy level of a chlorine atom in its ground state, and a total of 11 electrons in the p orbitals for the entire chlorine atom.

Key concepts

Electron Orbitals

Electron orbitals are regions around the nucleus of an atom where electrons are most likely to be found. They are not fixed paths but rather probability distributions that define where an electron might be at any given time. Each orbital can be visualized as a cloud-like region and can hold a maximum of two electrons with opposite spins.

There are several types of orbitals, known as s, p, d, and f, each with a characteristic shape. For instance, s orbitals have a spherical shape, while p orbitals have a dumbbell shape. Within each energy level of an atom, the orbitals are filled with electrons in a specific order, following the Aufbau principle, which states that each electron occupies the lowest energy orbital available.

In the context of a chlorine atom, the p orbitals become significant in the electron filling order after the 1s and 2s orbitals have been filled. With 17 electrons, it's the 3p orbitals that will not be completely filled, as they can accommodate a total of 6 electrons but in chlorine's case, they hold only 5 electrons in its ground state.

Principal Quantum Number

The principal quantum number, symbolized by the letter 'n', is one of four quantum numbers used to describe the unique quantum state of an electron. It is a positive integer that indicates the relative size and energy level of an electron's orbital. The value of 'n' begins at 1 and increases as the energy level of the orbital becomes higher, also generally increasing the distance the electron is from the nucleus.

For each value of the principal quantum number, there are n² orbitals. For example, when n=1 (the first energy level), there is only one s orbital, where n=2 has four orbitals (one s and three p orbitals), and so on. The principal quantum number is fundamental in determining the electron configuration of an atom, that is, the arrangement of electrons in orbitals around the nucleus.

In the example of the chlorine atom, the third energy level (n=3) contains 3s and 3p orbitals. The chlorine atom fills these up partially, leading to its electron configuration which influences its chemical properties and reactivity.

Ground State

The term 'ground state' refers to the lowest energy state of an atom or molecule, where all of the electrons are in the lowest available energy levels. It is the most stable and common state for an atom. Electrons fill up orbitals starting from the lowest energy level and then moving up to higher levels according to rules such as the Aufbau principle, Hund's Rule, and the Pauli Exclusion Principle.

The ground state electron configuration is particularly important because it determines the chemical properties of the atom, including how it will interact with other atoms. An excited state is the opposite of ground state, where one or more electrons have absorbed energy and moved to a higher energy orbital.

In the exercise, the chlorine atom's electron configuration represents its ground state configuration. With a full 1s, 2s, 2p, 3s orbitals and partially filled 3p orbitals, it showcases precisely how the chlorine atom's electrons are distributed in the lowest energy configuration possible under normal conditions.