Question

$$ \text { How many unpaired electrons are in a chlorine atom? } $$

Short answer

The chlorine atom has one unpaired electron.

Step-by-step solution

Write Electron Configuration for Chlorine

The electron configuration of chlorine can be written following the (n+l) rule (also known as Madelung's rule). For chlorine with atomic number 17, the electron configuration will be: 1s² 2s² 2p⁶ 3s² 3p⁵.

Identify Unpaired Electrons

Look specifically at the highest energy level (3), the p orbital has 5 electrons. The p orbital can hold up to six electrons. However, it only starts to pair up after each of the 3 p orbitals has one electron, therefore there is one unpaired electron in chlorine.

Key concepts

Electron Configuration

The electron configuration of an atom is a systematic arrangement of its electrons in orbitals around the nucleus. To find the electron configuration for chlorine, we use its atomic number, which is 17. This number tells us that chlorine has 17 electrons to arrange. Electrons are organized by filling from lower energy to higher energy orbitals. For chlorine, the electron configuration is written as:

• 1s²: 2 electrons in the first energy level
• 2s² 2p⁶: A total of 8 electrons in the second energy level, filling the 2s and 2p orbitals
• 3s² 3p⁵: 7 electrons in the third energy level, filling the 3s and partially filling the 3p orbitals

This detailed configuration helps in predicting the chemical properties of the element. Particularly, the electrons in the outermost energy levels matter the most for chemical reactivity.

Atomic Number

The atomic number of an element is the number of protons in the nucleus of its atoms. It also equals the number of electrons in a neutral atom, which is crucial for determining the electron configuration. Chlorine, with an atomic number of 17, has 17 protons and 17 electrons when neutral. The atomic number not only helps us identify elements but also gives insight into the element's position in the periodic table.
For instance, chlorine's atomic number places it in group 17 of the periodic table, classifying it as a halogen. This has implications for its reactivity and properties, as halogens are known for being highly reactive.
Thus, knowing the atomic number allows us to predict how chlorine behaves in chemical reactions, especially in forming bonds with other elements.

P Orbital

The p orbital is a type of atomic orbital that can hold a maximum of 6 electrons. In each energy level above the first, the p orbitals are present, forming part of the electron cloud where electrons might be found around the nucleus. Each p orbital has a unique shape, often described as a pair of lobes on opposite sides of a node.
For chlorine, the 3p orbital contains 5 of the 6 possible electrons. Electrons are filled according to Hund's rule, meaning that one electron occupies each p orbital before any pairing occurs. Thus, in the 3p orbital of chlorine, five electrons distribute as follows:

• 3px with 1 electron
• 3py with 1 electron
• 3pz with 2 electrons

This distribution results in one unpaired electron, which impacts chlorine's ability to form bonds and participate in chemical reactions.