Question

Intepret Data In a methane molecule (CH \(_{4}\) ), there are four single covalent bonds. In an octane molecule \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\), there are 25 single covalent bonds. How does the number of bonds affect the dispersion forces in samples of methane and octane? Which compound is a gas at room temperature? Which is a liquid?

Short answer

The number of covalent bonds affects dispersion forces in molecules, with stronger dispersion forces present in larger molecules with more electrons. Methane (CH$_{4}$) has 4 single covalent bonds and weaker dispersion forces, making it a gas at room temperature. Octane (C$_{8}$H$_{18}$) has 25 single covalent bonds and stronger dispersion forces, making it a liquid at room temperature.

Step-by-step solution

Identify the number of covalent bonds in methane (CH4) molecule

Methane has one carbon atom covalently bonded to four hydrogen atoms. Therefore, there are 4 single covalent bonds in a methane molecule.

Identify the number of covalent bonds in octane (C8H18) molecule

Octane has 8 carbon atoms and 18 hydrogen atoms. There are 7 single covalent bonds between the carbon atoms, forming a continuous chain, and there are 18 single covalent bonds between carbon and hydrogen atoms. So, there are a total of 25 single covalent bonds in an octane molecule. #Step 2: Understand dispersion forces and how they are affected by the number of bonds#

Dispersion forces and their relationship with the number of covalent bonds

Dispersion forces, also known as London dispersion forces or van der Waals forces, are weak intermolecular forces that occur between nonpolar molecules. Dispersion forces are induced by fluctuations in the electron distribution within a molecule, resulting in temporary dipoles that create transient attractive forces with neighboring molecules. The larger the molecule and the greater the number of electrons, the stronger the dispersion forces between molecules. As the number of covalent bonds in a molecule increases, so does the size of the molecule and the number of electrons present. Therefore, a higher number of covalent bonds will increase the dispersion forces between molecules, holding them more tightly together. #Step 3: Compare the dispersion forces in methane and octane#

Comparison of dispersion forces in methane and octane

Methane has four single covalent bonds, while octane has 25 single covalent bonds. Octane is a larger molecule with more electrons than methane, which leads to stronger dispersion forces between octane molecules compared to methane. #Step 4: Deduce the state of compounds at room temperature based on dispersion forces#

Determine the state of methane and octane at room temperature

Since octane has stronger dispersion forces, it is more difficult for its molecules to separate and become a gas compared to methane. Therefore, at room temperature, methane is likely to be a gas, while octane is a liquid. In conclusion, the number of covalent bonds affects the dispersion forces in molecules, with stronger dispersion forces present in larger molecules with more electrons. Methane, with fewer covalent bonds and weaker dispersion forces, is a gas at room temperature, while octane, with more covalent bonds and stronger dispersion forces, is a liquid.

Key concepts

Covalent Bonds

Covalent bonds are a type of chemical bond where two atoms share a pair of electrons. This type of bonding usually occurs between nonmetals. In a covalent bond, each atom contributes one electron to the pair, creating a stable electron configuration similar to that of noble gases. This sharing of electrons helps atoms achieve stability by filling their outermost electron shells.

In the context of our exercise, covalent bonds significantly influence molecular properties by determining molecular size, shape, and the ability of molecules to interact with each other.

• Methane (CH extsubscript{4}) has 4 single covalent bonds, formed by one carbon atom sharing electrons with four hydrogen atoms.
• Octane (C extsubscript{8}H extsubscript{18}) has 25 covalent bonds: 7 between carbon atoms and 18 between carbon and hydrogen atoms, creating a longer chain structure.

The number of covalent bonds, as we'll see, plays a crucial role in affecting intermolecular forces and, consequently, the physical state of the substance.

Methane

Methane, with the chemical formula CH extsubscript{4}, is the simplest alkane and a key component of natural gas. It is a tetrahedral molecule, meaning its atoms are arranged in a three-dimensional shape with a central carbon atom symmetrically surrounded by four hydrogen atoms. This symmetric shape makes methane nonpolar.
Due to its small size and limited number of electrons, methane exhibits very weak dispersion forces. These are the weakest type of intermolecular forces and arise due to temporary changes in electron distribution, which create momentary dipoles. Consequently, at room temperature, methane exists in a gaseous state since its molecules do not stick together strongly enough to form a liquid.
Methane's properties are important in understanding fundamental differences in intermolecular forces when compared to larger molecules like octane.

Octane

Octane, with the chemical formula C extsubscript{8}H extsubscript{18}, is a more complex alkane compared to methane. It is composed of a long chain of carbon atoms, bound together and with hydrogen atoms attached, making it larger and heavier. With 25 single covalent bonds, octane has a greater number of electrons than methane.

The additional electrons and larger molecular size contribute to stronger dispersion forces. These forces make it more difficult for octane molecules to separate from each other, because the temporary dipoles induced by electron movement are more substantial. Consequently, octane remains a liquid at room temperature, unlike methane.

Understanding octane's properties provides insight into how molecular size impacts physical states and the strength of intermolecular forces.

Intermolecular Forces

Intermolecular forces are forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions). In our exercise, the focus is on dispersion forces, which are a type of van der Waals force acting between nonpolar molecules.

• Dispersion forces, or London dispersion forces, are temporary and arise from fluctuations in electron density within molecules, leading to transient dipoles.
• These forces increase with greater numbers of electrons and larger molecular sizes.

For methane, with fewer covalent bonds and electrons, the dispersion forces are weak, causing it to be a gas at room temperature.
Octane, with more covalent bonds, has stronger dispersion forces due to its larger electron cloud, allowing it to exist as a liquid under the same conditions. Understanding these forces is essential for predicting and explaining the physical properties of substances.