Question

Use an example to illustrate each of the following terms: lone pair, Lewis structure, octet rule, bond length.

Short answer

A lone pair is unshared electrons, Lewis structure shows atom arrangement, the octet rule indicates full valence, and bond length is the distance between bonded nuclei.

Step-by-step solution

Understanding Lone Pair

A lone pair refers to a pair of valence electrons that are not shared with another atom in a molecule. For example, in water (H₂O), oxygen has two lone pairs of electrons.

Drawing a Lewis Structure

A Lewis structure is a diagram that represents the arrangement of atoms within a molecule, showing the bonding between atoms and the lone pairs of electrons. To draw the Lewis structure of water (H₂O): - Place the oxygen atom in the center since it is more electronegative than hydrogen. - Connect each hydrogen atom to the oxygen with a single line, which represents a single covalent bond. - Show the two lone pairs as dots around the oxygen atom.

Applying the Octet Rule

The octet rule states that atoms tend to form bonds in a way that each atom has eight electrons in its valence shell. In the water molecule, oxygen fulfills the octet rule by having two bonds with hydrogen and two lone pairs, making a total of eight electrons around it. Each hydrogen achieves a full valence shell (which is two electrons for hydrogen).

Explaining Bond Length

Bond length is the average distance between the nuclei of two bonded atoms. In water, the bond length of the O-H bond is approximately 95.7 picometers. Bond lengths vary depending on the type of atoms and the type of bond (single, double, triple).

Key concepts

Lone Pair

In chemistry, a lone pair, also known as an unshared pair, refers to a pair of valence electrons that are not involved in chemical bonding. These electrons are localized around a single atom. Here’s an easy way to think of it: while bonded electrons are socially interacting with other atoms, lone pairs stick to themselves!

• Lone pairs are crucial for determining the shape of a molecule.
• They often influence how a molecule behaves chemically during reactions.

Take water (H₂O) as an example. The oxygen atom in water has two lone pairs. These pairs of electrons stay close to the oxygen to help it maintain its shape and stability.
Besides impacting molecular shape, lone pairs affect the polarity of a molecule. So, when studying molecular geometry or predicting molecular interactions, never underestimate the power of lone pairs!

Octet Rule

The octet rule is a fundamental concept in chemistry that helps explain why atoms form certain types of bonds. According to this rule, atoms tend to bond in a manner that results in each atom having eight electrons in its valence shell. This gives the atom stability, similar to the noble gases that naturally have complete valence shells.

• Electrons can be shared (as in covalent bonds) or transferred (as in ionic bonds) to achieve this stable configuration.
• The octet rule particularly applies to main-group elements, especially carbon, nitrogen, oxygen, and the halogens.

In the molecule of water, oxygen achieves the octet by sharing its two extra electrons with hydrogen atoms, while each hydrogen atom shares one electron with oxygen to fulfill their valence of two, thus gaining stability. Although hydrogen is an exception to the octet rule, seeking only two electrons to resemble helium, for most elements, the octet rule is a guiding principle.
Violations or exceptions to the octet rule can occur, particularly in transition metals and in molecules with an odd number of electrons. But for main-group chemistry, this rule is a handy tool for predicting bonding patterns.

Bond Length

Bond length measures how far apart two bonded nuclei are from one another. It's like the peacekeeping distance that atoms maintain when they share electrons. The length of a bond is determined by the types of atoms and the number of bonds they form with each other.

• Single bonds are the longest because they involve just a pair of shared electrons.
• Double bonds are shorter than single bonds, and triple bonds are the shortest, due to the increased sharing of electron pairs.

In the case of the water molecule (H₂O), the O-H bonds are about 95.7 picometers long. This specific bond length results from the sizes of the oxygen and hydrogen atoms and the single covalent bonds between them.
Understanding bond length is crucial for predicting the physical properties of molecules. Shorter bonds are generally stronger, affecting the stability and reactivity of the molecules they compose. Therefore, when calculating energy and anticipating molecular behavior, bond length is a key parameter.