Question

(a) What are valence electrons? (b) How many valence electrons does a nitrogen atom possess? (c) An atom has the electron configuration \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{2}\). How many valence electrons does the atom have?

Short answer

(a) Valence electrons are the electrons in the outermost energy level (shell) of an atom, which participate in chemical reactions and form chemical bonds. (b) A nitrogen atom has 5 valence electrons, as its electron configuration is \(1s^2 2s^2 2p^3\). (c) The given atom, with the electron configuration \(1s^2 2s^2 2p^6 3s^2 3p^2\), has 4 valence electrons, as the outermost energy level contains 2 electrons in the 3s orbital and 2 in the 3p orbital.

Step-by-step solution

(a) Defining valence electrons

Valence electrons are the electrons in the outermost energy level (shell) of an atom. These electrons are important because they are the ones that participate in chemical reactions and form chemical bonds with other atoms.

(b) Valence electrons in a nitrogen atom

A nitrogen atom has 7 electrons residing in its energy levels. The electron configuration of nitrogen is \(1s^2 2s^2 2p^3\). Here, the outermost energy level is the second energy level (n=2), which contains 5 electrons (2 in the 2s orbital and 3 in the 2p orbital). So a nitrogen atom has 5 valence electrons.

(c) Valence electrons in the given atom

The given electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^2\). The outermost energy level is the third level (n=3), containing 4 electrons (2 in the 3s orbital and 2 in the 3p orbital). Therefore, the atom has 4 valence electrons.

Key concepts

Understanding Electron Configuration

Knowing an atom's electron configuration is like having a roadmap of its electrons. It reveals how electrons are distributed among the shells and subshells around the nucleus. Consider it as the distribution of seats in an auditorium that tells you where every person is seated. The configuration follows a set of rules, such as the Pauli exclusion principle which states that no two electrons can have the same set of quantum numbers, and Hund's rule that electrons must occupy every orbital singly before any orbital is doubly occupied.

The configurations help us predict many properties of an atom, such as its magnetism, its reactivity, and even the types of bonds it can form with other atoms. As seen in the exercise solution, we use it to figure out that nitrogen, with the configuration of 1s^2 2s^2 2p^3, has five valence electrons that are key players in chemical interactions.

The Role of Valence Electrons in Chemical Reactions

Valence electrons serve a starring role on the stage of chemical reactions. They are like a character's dialogue in a play, they tell you exactly how that atom will interact with others. The more valence electrons there are, the more lines the atom has in the reaction. These electrons can be shared with other atoms to create covalent bonds or transferred to form ionic bonds.


In the case of nitrogen from our exercise with five valence electrons, it’s eager to form three covalent bonds to fill up its outer shell. This is why nitrogen is often found in ammonia (NH₃), where it shares its valence electrons with three hydrogen atoms. Understanding this concept allows us to predict and explain the mechanisms behind the substances' transformations during chemical reactions.

Chemical Bonds: The Glue that Holds Atoms Together

Chemical bonds are the glue that keeps atoms stuck together in molecules. Based on the behavior of valence electrons, these bonds can be covalent, where atoms share electrons, or ionic, where one atom gives up its valence electrons to another. There's also metallic bonding, which you can think of as a 'sea' of electrons that moves freely between metal atoms.

Understanding Chemical Bonding Through the Exercise

Referring back to our example atom with the configuration 1s^2 2s^2 2p^6 3s^2 3p^2, this atom has four valence electrons, which indicates it might form two covalent bonds. Being able to draw these connections from electron configuration to bond formation is essential for understanding how molecules are constructed, which is crucial for fields ranging from materials science to biochemistry.