Question

Give the total number of valence electrons in each of the following molecules. a. \(\mathrm{N}_{2} \mathrm{O}\) b. \(\mathrm{B}_{2} \mathrm{H}_{6}\) c. \(\mathrm{C}_{3} \mathrm{H}_{8}\) d. \(\mathrm{NCl}_{3}\)

Short answer

The total number of valence electrons for each molecule is: a. N₂O: 16 valence electrons b. B₂H₆: 12 valence electrons c. C₃H₈: 20 valence electrons d. NCl₃: 26 valence electrons

Step-by-step solution

Identify the atoms in each molecule and their valence electrons

Using the periodic table, we can determine the valence electrons of each element: N (Nitrogen) has 5 valence electrons O (Oxygen) has 6 valence electrons B (Boron) has 3 valence electrons H (Hydrogen) has 1 valence electron C (Carbon) has 4 valence electrons Cl (Chlorine) has 7 valence electrons

Find the total number of valence electrons for each molecule

a. N₂O In this molecule, there are 2 Nitrogen atoms and 1 Oxygen atom. Total valence electrons = (No. of Nitrogen atoms x valence electrons for Nitrogen) + (No. of Oxygen atoms x valence electrons for Oxygen) = (2 x 5) + (1 x 6) = 10 + 6 = 16 valence electrons b. B₂H₆ In this molecule, there are 2 Boron atoms and 6 Hydrogen atoms. Total valence electrons = (No. of Boron atoms x valence electrons for Boron) + (No. of Hydrogen atoms x valence electrons for Hydrogen) = (2 x 3) + (6 x 1) = 6 + 6 = 12 valence electrons c. C₃H₈ In this molecule, there are 3 Carbon atoms and 8 Hydrogen atoms. Total valence electrons = (No. of Carbon atoms x valence electrons for Carbon) + (No. of Hydrogen atoms x valence electrons for Hydrogen) = (3 x 4) + (8 x 1) = 12 + 8 = 20 valence electrons d. NCl₃ In this molecule, there are one Nitrogen atom and three Chlorine atoms. Total valence electrons = (No. of Nitrogen atoms x valence electrons for Nitrogen) + (No. of Chlorine atoms x valence electrons for Chlorine) = (1 x 5) + (3 x 7) = 5 + 21 = 26 valence electrons

Present the final answer

The total number of valence electrons for each molecule is: a. N₂O: 16 valence electrons b. B₂H₆: 12 valence electrons c. C₃H₈: 20 valence electrons d. NCl₃: 26 valence electrons

Key concepts

Chemical Bonding

Understanding the concept of chemical bonding is fundamental in chemistry, as it is the key to how atoms or groups of atoms interact and join to form molecules. At its core, chemical bonding is all about the valence electrons.

Valence electrons are the outermost electrons of an atom and are primarily responsible for the chemical properties of that atom. When atoms bond, they do so to achieve a more stable electronic configuration, often by either sharing, losing, or gaining valence electrons to attain a full outer electron shell.

There are different types of chemical bonds, including ionic, covalent, and metallic. Ionic bonding occurs when atoms transfer electrons, while covalent bonding happens through the sharing of electrons. Metallic bonds are found in metals, where electrons are delocalized and able to move freely throughout the lattices of metal atoms.

The exercise given illustrates the counting of valence electrons, which is crucial in predicting how atoms will bond and what molecular structure will result. For example, in a molecule of N₂O, there are 16 valence electrons which dictates its molecular shape and how its constituent atoms bond together.

Periodic Table

The periodic table is an organized chart of chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. Its structure reflects the periodic law which states that certain properties of the elements repeat periodically when arranged by atomic number.

Key to understanding the periodic table is recognizing that elements are grouped into periods (horizontal rows) and groups (vertical columns) with elements in the same group having similar chemical and physical properties, most notably the number of valence electrons. For instance, all elements in group 1 have one valence electron, making them highly reactive.

In the context of our exercise, the periodic table helps in quickly identifying that Nitrogen, as a group 15 element, has 5 valence electrons, while Oxygen in group 16 has 6. This consistent pattern means that with practice, predicting the valence electrons of an atom becomes more intuitive, leading to easier assessments of molecular composition.

Molecular Composition

Molecular composition describes the numbers and types of atoms present in a molecule and how they are arranged. It reveals the exact number of atoms of each element a molecule contains and thus gives insight into the molecule's properties and reactions it may undergo.

The calculation of valence electrons, as shown in the exercise, plays an instrumental role in predicting the molecular composition. For example, knowing that Carbon has 4 valence electrons and Hydrogen has 1 allows us to understand why propane (C₃H₈) has 3 Carbon atoms bonded together, with each Carbon also bonded to Hydrogen atoms.

Besides satisfying the octet rule, which states that atoms typically prefer having eight valence electrons in their outermost shell, molecular composition is also influenced by how these electrons can be shared between atoms to achieve chemical stability. Thus, molecular composition not only tells us about the quantities of atoms but also hints at the possible three-dimensional shape of the molecule and how it might interact with other molecules.