Question

Tetrafluoroethylene, \(\mathrm{C}_{2} \mathrm{~F}_{4}\) is the starting material for the synthesis of the polymer polytetrafluoroethylene (PTFE), one form of which is known as Teflon. Tetrafluoroethylene has a dipole moment of zero. Propose a structural formula for this molecule.

Short answer

Answer: The structural formula for tetrafluoroethylene is given as: F F \ / C = C / \ F F This structure has a zero dipole moment due to its symmetrical arrangement, with each fluorine atom's polarity canceling out the others, thus making tetrafluoroethylene nonpolar.

Step-by-step solution

Understand dipole moment

A molecule's dipole moment is a measure of its overall charge distribution and polarity. In a simple molecule, the dipole moment is the product of the charge and the distance between the centers of positive and negative charge. If the dipole moment is zero, that means the molecule is nonpolar, and the net charge distribution is symmetrical.

Determine the number of atoms in the molecule

Since tetrafluoroethylene has a chemical formula of C2F4, it consists of 2 carbon atoms and 4 fluorine atoms.

Determine possible arrangements of the atoms in the molecule to have a zero dipole moment

To find the structure with a zero dipole moment, we need to arrange the atoms in such a way that the electronegativity difference has a symmetrical distribution. Given that carbon and fluorine form single bonds, we can create a carbon-carbon double bond with two fluorine atoms bonded to each carbon atom. Recalling that fluorine is more electronegative than carbon, these bonds should be oriented oppositely to make sure the polarities cancel each other out.

Propose a structural formula for the molecule

Based on our analysis in Step 3, the structural formula for tetrafluoroethylene is: F F \ / C = C / \ F F With two carbon atoms bonded by a double bond, and two fluorine atoms bonded to each carbon atom, oriented oppositely, the dipole moments cancel each other out, resulting in a zero dipole moment. The proposed molecule is also symmetrical, which is consistent with a zero dipole moment.

Key concepts

Dipole Moment

Understanding dipole moment is crucial for students delving into the world of chemistry, especially when it involves molecular polarity. The dipole moment is an indicator of the separation of charge within a molecule and is measured in Debye units. It is a vector quantity, which means it has both magnitude and direction. Essentially, it's the product of the amount of charge separated and the distance between the charges.

For instance, in a water molecule (H_2O), the oxygen atom is more electronegative than the hydrogen atoms, leading to a partial negative charge near the oxygen and a partial positive charge near the hydrogens. This separation creates a dipole moment. However, in molecules like tetrafluoroethylene (C_2F_4), the symmetry of the molecule means that any local dipoles cancel out, resulting in a total dipole moment of zero. This property has profound implications on the molecule's reactivity and interaction with other substances.

Chemical Structure

The chemical structure of a compound tells us about the arrangement of atoms and can explain many of its properties. In tetrafluoroethylene (C_2F_4), the chemical structure is a linear chain of two carbon atoms joined by a double bond, with fluorine atoms bound to each carbon. This layout is crucial because it creates a balanced molecule where the pull of the highly electronegative fluorine atoms is equally distributed.

Understanding a molecule's structure is not just limited to knowing its shape or form; it’s about recognizing how the arrangement impacts the molecule's overall polarity and why some molecules, despite having polar bonds, end up being nonpolar due to their symmetrical structural organization.

Polarity in Molecules

When exploring polarity in molecules, it's important to differentiate between polar bonds and polar molecules. A polar bond is a result of a significant difference in electronegativity between two atoms, leading to an uneven distribution of electrons. However, a molecule may contain polar bonds and still be nonpolar, as is the case with tetrafluoroethylene (C_2F_4).

The overall polarity of a molecule is determined not just by the presence of polar bonds, but also by the geometry of the molecule. If the shape of the molecule allows for the dipole moments of each polar bond to cancel out, as seen with the symmetric arrangement in C_2F_4, the molecule itself is nonpolar. This understanding is key to predicting the behavior of molecules in different chemical reactions and in their interactions with other substances.

Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE), better known by its trade name, Teflon, is a polymer formed through the polymerization of tetrafluoroethylene (C_2F_4). This polymer is renowned for its remarkable properties, such as non-reactivity, low friction, and high thermal stability, making it ideal for a wide array of applications, from non-stick cookware to aerospace engineering.

PTFE’s extraordinary characteristics are a direct result of its chemical structure. Each repeating unit of PTFE consists of a carbon backbone flanked by fluorine atoms. The strength of the carbon-fluorine bonds and the covering of the carbon chain by the fluorine atoms confer PTFE its resistance to chemicals and heat. Its creation and the understanding of its properties are perfect examples of how a molecule's structure can determine its practical uses in everyday life.