Question

Explain how carbon tetrachloride can have polar bonds but still be a nonpolar molecule.

Short answer

Though Carbon Tetrachloride (CCl4) has polar bonds, due to its symmetrical tetrahedral shape, the individual dipole moments of the C-Cl bonds cancel each other out, resulting in a nonpolar molecule.

Step-by-step solution

Explore the concept of polar bonds

Polar bonds are formed when two different atoms share electrons unequally in a covalent bond. In the case of Carbon Tetrachloride (CCl4), the bond between Carbon (C) and Chlorine (Cl) is polar because Cl is more electronegative than C and attracts the shared pair of electrons closer to itself.

Discuss the structure of carbon tetrachloride

Carbon Tetrachloride has a tetrahedral geometry, which means the central carbon atom is bonded to the four chlorine atoms in a way that they are roughly positioned at the corners of a tetrahedron, symmetrical around the carbon atom.

Understand molecule polarity

A molecule is considered polar if it has a net dipole moment. However, in the case of CCl4, the symmetry of the tetrahedral shape ensures that the individual polar C-Cl bonds cancel each other out. Thus, despite having polar bonds, CCl4 does not have an overall dipole moment and is therefore a nonpolar molecule.

Key concepts

Polar Bonds

A polar bond is a type of covalent bond in which the electrons shared between two atoms are not shared equally. This unequal sharing occurs because the atoms involved in the bond have different electronegativities. Electronegativity is the measure of an atom's ability to attract and hold electrons. When one atom is more electronegative than the other, it will draw the shared electrons closer to itself, creating a polar bond. The atom with higher electronegativity gains a slight negative charge, while the other atom acquires a slight positive charge.

• Example: In a carbon tetrachloride molecule, each chlorine atom (Cl) has a higher electronegativity than the central carbon atom (C).
• As a result, the electrons spend more time closer to the chlorine atoms, making each C-Cl bond polar.

This results in a bond with partial charges at each end, creating a dipole moment along each C-Cl bond.

Tetrahedral Geometry

The tetrahedral geometry is a common molecular shape where a central atom is connected to four other atoms, placed at the corners of a tetrahedron. This shape is highly symmetrical and plays a crucial role in determining the overall polarity of a molecule. In the case of carbon tetrachloride (CCl4), the central carbon atom forms four polar bonds with chlorine atoms.

• The arrangement is such that it equally distributes these bonds in 3D space.
• Each bond angle is approximately 109.5 degrees, which helps maximize the distance between the chlorine atoms.

Due to the tetrahedral symmetry, the polarities of the C-Cl bonds cancel each other out. This symmetry eliminates any net dipole moment, causing CCl4 to be a nonpolar molecule, despite having polar bonds.

Electronegativity

Electronegativity is a fundamental concept in chemistry that helps predict how atoms will interact with each other in a molecule. It describes an atom's ability to attract and hold onto electrons within a chemical bond. Generally, atoms with higher electronegativities tend to attract electrons more strongly than those with lower electronegativities.

• For instance, chlorine is more electronegative than carbon, making it better at pulling shared electrons towards itself in a C-Cl bond.
• Electronegativity differences between bonding atoms lead to bond polarity, where electrons are unequally shared.

This concept is crucial in understanding why certain molecules have polar bonds or are nonpolar. As in CCl4, although each C-Cl bond is polar due to chlorine's higher electronegativity, the symmetrical tetrahedral arrangement cancels these effects, rendering the molecule nonpolar overall.