Question

Which of the substances \(\mathrm{CdBr}_{2}, \mathrm{P}_{4}, \mathrm{BrF}_{3}, \mathrm{MgO}, \mathrm{NF}_{3}, \mathrm{BaCl}_{2}\) \(\mathrm{POCl}_{3}\), and LiBr are: (a) largely ionic? (b) nonpolar covalent? (c) polar covalent?

Short answer

Largely ionic: \(\mathrm{CdBr}_2, \mathrm{MgO}, \mathrm{BaCl}_2, \mathrm{LiBr}\). Nonpolar covalent: \(\mathrm{P}_4\). Polar covalent: \(\mathrm{BrF}_3, \mathrm{NF}_3, \mathrm{POCl}_3\).

Step-by-step solution

Identify Ionic Compounds

Ionic compounds are typically formed between metals and non-metals and involve the transfer of electrons from the metal to the non-metal. Look for compounds involving elements from the first two groups (alkali and alkaline earth metals) with other non-metals or halogens. In the list, - \(\mathrm{CdBr}_2\) (cadmium is a transition metal and forms ionic bonds with bromine), - \(\mathrm{MgO}\) (magnesium is an alkaline earth metal bonding with oxygen), - \(\mathrm{BaCl}_2\) (barium is an alkaline earth metal bonding with chlorine), - \(\mathrm{LiBr}\) (lithium is an alkali metal bonding with bromine) are largely ionic.

Identify Nonpolar Covalent Compounds

Nonpolar covalent compounds are typically formed between non-metals with similar electronegativities, often involving the same atom or symmetrical structures where dipole moments cancel out. In this list, - \(\mathrm{P}_4\), where phosphorus molecules are bonded to themselves symmetrically, is a nonpolar covalent compound.

Identify Polar Covalent Compounds

Polar covalent compounds are those formed between non-metals with different electronegativities, leading to unequal sharing of electrons and the creation of dipoles. Analyze the remaining substances:- \(\mathrm{BrF}_3\) has a trigonal bipyramidal shape causing net dipoles,- \(\mathrm{NF}_3\) has a trigonal pyramidal shape with a net dipole,- \(\mathrm{POCl}_3\) forms a tetrahedral structure where there is unequal sharing of electrons between central phosphorus and surrounding oxygens and chlorines.These are polar covalent compounds.

Key concepts

Ionic Compounds

Ionic compounds are a fascinating aspect of chemical bonding. These compounds form when electrons transfer from one atom to another, typically involving a metal and a nonmetal. This exchange produces ions: the metal loses electrons to become a positively charged cation, while the nonmetal gains those electrons to become a negatively charged anion. The electrostatic attraction between these oppositely charged ions forms a strong bond, resulting in an ionic compound.

For example, compounds like \(\text{CdBr}_2\), \(\text{MgO}\), \(\text{BaCl}_2\), and \(\text{LiBr}\) are largely ionic. The metal elements like cadmium, magnesium, barium, and lithium bond with nonmetals bromine, oxygen, and chlorine. This results in compounds with high melting and boiling points and typically solid states at room temperature.

Knowing characteristics like these helps determine if a given compound is ionic:

• Formation involves metals and nonmetals.
• High melting and boiling points.
• Typically solid at room temperature.
• Conducts electricity when dissolved in water, as ions are free to move.

Covalent Compounds

Covalent compounds form when atoms share electrons, typically between nonmetals. This type of chemical bond occurs because the atoms involved have similar electronegativities, allowing for an equal or nearly equal sharing of electrons. This results in molecules rather than the three-dimensional lattices seen in ionic compounds.

There are different types of covalent bonds, which are influenced by the molecular geometry and the atoms involved:

• Nonpolar Covalent Bonds: These occur when atoms share electrons equally. A classic example is \(\text{P}_4\), where phosphorus atoms form a nonpolar, symmetrical molecule.
• Polar Covalent Bonds: In these bonds, the electrons are not shared equally due to a difference in electronegativity between the two atoms. These result in a molecule having a positive and a negative pole. Compounds like \(\text{BrF}_3\), \(\text{NF}_3\), and \(\text{POCl}_3\) fall into this category because they involve atoms with differing electronegativities, creating dipoles within the molecule.

Understanding how atoms share electrons in covalent compounds is crucial for predicting molecular properties and reactivities.

Polarity in Molecules

Polarity in molecules is a key concept in understanding molecular behavior and interactions. It describes how electrons are distributed in a molecule, which affects its dipole moment. This uneven sharing of electrons arises due to differences in electronegativity between bonds within a molecule, leading to polar covalent bonds and resulting in polar molecules.

Here's how you can determine the polarity of a molecule:

• If a molecule has a \(\text{symmetric shape}\) and the bond polarities cancel out (like in some nonpolar covalent compounds), the molecule is nonpolar.
• If a molecule has an \(\text{asymmetric shape}\) or has polar bonds that do not cancel out, it becomes polar. For example, in \(\text{BrF}_3\) and \(\text{NF}_3\), the shapes cause the dipoles not to cancel, resulting in polar molecules.

Polarity influences properties like solubility, boiling and melting points, and interaction with other molecules. Polar molecules tend to dissolve well in polar solvents (like water), whereas nonpolar molecules do not. This principle is crucial in predicting how substances interact in various environments.