Question

List the steps you take to decide (a) whether or not. a covalent bond is polar and (b) whether or not a molecule is polar.

Short answer

To determine whether a covalent bond is polar or not, follow these steps: 1) Find the electronegativity values of the atoms forming the bond; 2) Calculate the electronegativity difference (if < 0.5, bond is non-polar; if between 0.5 and 1.9, bond is polar, and if ≥ 2, bond is ionic). To determine whether a molecule is polar or not, follow these steps: 1) Determine the molecule's geometry based on VSEPR theory; 2) Identify polar bonds within the molecule; 3) Analyze the molecular geometry and bond polarity (if no polar bonds, molecule is non-polar; if polar bonds are symmetrically distributed, molecule is non-polar, if polar bonds are not symmetrically distributed, the molecule is polar).

Step-by-step solution

Find the electronegativity values of the atoms involved in the covalent bond

Look up the electronegativity values of the two atoms involved in the covalent bond from a periodic table or a reference book. Electronegativity represents an atom's ability to attract electrons in a covalent bond.

Calculate the electronegativity difference

Subtract the smaller electronegativity value from the larger one to find the electronegativity difference between the two atoms.

Determine the polarity of the covalent bond

Based on the electronegativity difference, determine if the covalent bond is polar or non-polar: - If the electronegativity difference is less than 0.5, the bond is considered non-polar covalent. - If the electronegativity difference is between 0.5 and 1.9, the bond is considered polar covalent. - If the electronegativity difference is equal or greater than 2, the bond is considered ionic, not covalent. #b. Determining whether a molecule is polar or not#

Determine the molecule's geometry

Examine the molecule's structure and identify its shape based on the arrangement of atoms and the number of regions of electron density around the central atom (VSEPR theory). Some common molecular geometries include linear, bent, trigonal planar, tetrahedral, and trigonal bipyramidal.

Identify polar bonds within the molecule

Using the same process mentioned in section (a), identify if the molecule contains polar covalent bonds or not.

Analyze the molecular geometry and bond polarity

Analyze the distribution of polar bonds and the overall molecular shape. If the molecule has no polar bonds, it is a non-polar molecule. If the molecule has polar bonds but they are symmetrically distributed (resulting in no net dipole moment), it is a non-polar molecule. If there are polar bonds and they are not symmetrically distributed, the molecule is polar. So, to determine whether a molecule is polar or not, consider both the distribution of polar covalent bonds and the overall molecular geometry.

Key concepts

Electronegativity

Understanding the concept of electronegativity is fundamental when studying the polarity of molecules. Electronegativity refers to the ability of an atom to attract shared electrons in a covalent bond towards itself. It's a qualitative measure, and while it doesn't have a standardized unit, it offers crucial insight into how electrons are distributed in a molecule.

Elements on the periodic table have varying electronegativity values, with fluorine being the most electronegative element. These values can be found in a variety of reference sources. When two atoms form a covalent bond, the difference in their electronegativity values can determine the type of bond formed. A large difference suggests a polar bond, as electrons are more attracted to one atom, while a minor difference indicates a non-polar bond where electrons are more evenly shared.

Covalent Bonds

Covalent bonds are the glue that holds molecules together. They involve the sharing of electron pairs between atoms, and the distribution of these shared electrons is based on the electronegativity of each atom involved. If the atoms have similar electronegativity values, the electrons are shared more or less equally, resulting in a non-polar covalent bond.

However, if one atom is significantly more electronegative than the other, it will attract the shared electrons more strongly. This creates a polar covalent bond, where one end of the bond has a slight negative charge and the other end has a slight positive charge. Understanding this concept is crucial in predicting how molecules will interact with each other and their environment.

Molecular Geometry

The 3D arrangement of atoms within a molecule is known as its molecular geometry. This structure is vital for understanding the physical and chemical properties of the molecule, including its polarity. Even if a molecule contains polar bonds, the overall geometry can influence whether the molecule is polar or non-polar.

The symmetry of the molecule plays a key role here. A symmetric molecule with polar bonds may end up being non-polar overall because the individual polarities cancel out. Conversely, an asymmetric molecule with polar bonds will likely be polar. For instance, in a bent molecule like water, the polar O-H bonds contribute to an overall dipole, making water a polar molecule.

VSEPR Theory

VSEPR theory, which stands for Valence Shell Electron Pair Repulsion theory, explains molecular geometry based on the repulsion between electron pairs in the valence shell of the central atom. By predicting the arrangement of these electron pairs, the theory helps determine the shape of the molecule which, in combination with bond polarity, decides the overall polarity of the molecule.

For example, carbon dioxide (CO₂) is linear, so the polarities of the C=O bonds cancel each other out, leading to a non-polar molecule. Conversely, the bent shape of water (H₂O) prevents the polar O-H bonds from cancelling, making water polar. VSEPR theory is an indispensable tool when studying molecular shapes and their impact on the physical properties and behaviors of substances.