Question

Which of the following compounds are likely to be ionic? Which are likely to be molecular? \(\mathrm{CH}_{4},\) NaBr, \(\mathrm{BaF}_{2}, \mathrm{CCl}_{4}, \mathrm{ICl}, \mathrm{CsCl}, \mathrm{NF}_{3}\)

Short answer

Ionic: NaBr, BaF₂, CsCl; Molecular: CH₄, CCl₄, ICl, NF₃.

Step-by-step solution

Understanding Ionic Compounds

Ionic compounds typically form between atoms with large differences in electronegativity. Generally, this means a metal atom and a nonmetal atom combine, where the metal loses electrons to become a cation, and the nonmetal gains electrons to become an anion.

Identifying Molecular Compounds

Molecular (or covalent) compounds form between nonmetals, where atoms share electrons to achieve full outer shells. These are usually composed of nonmetal atoms bonded together.

Analyze Each Compound

Now let's evaluate each given compound based on the above definitions: - **CH₄ (Methane):** Composed entirely of nonmetals (carbon and hydrogen), so it's likely molecular. - **NaBr (Sodium bromide):** Composed of a metal (sodium) and a nonmetal (bromine), so it's likely ionic. - **BaF₂ (Barium fluoride):** Contains a metal (barium) and a nonmetal (fluorine), indicating an ionic compound. - **CCl₄ (Carbon tetrachloride):** Composed of nonmetals (carbon and chlorine), suggesting it is molecular. - **ICl (Iodine monochloride):** Only involves nonmetals (iodine and chlorine), which classifies it as molecular. - **CsCl (Cesium chloride):** Includes a metal (cesium) and a nonmetal (chlorine), so it is likely ionic. - **NF₃ (Nitrogen trifluoride):** Composed of only nonmetals (nitrogen and fluorine), indicating a molecular compound.

Classify Compounds

Based on the analysis in Step 3: - Ionic Compounds: NaBr, BaF₂, CsCl - Molecular Compounds: CH₄, CCl₄, ICl, NF₃

Key concepts

Electronegativity

Electronegativity is a measure of how strongly an atom attracts electrons in a chemical bond. It plays a crucial role in determining the type of bond that forms between atoms. When two atoms have a significant difference in electronegativity, the more electronegative atom will attract the electron more strongly. This often results in one atom fully taking an electron from the other, leading to ionic bonding. For molecules with similar electronegativities, electrons are shared more equally, often resulting in covalent bonding.

• Elements with higher electronegativity, like fluorine, attract electrons more strongly.
• Elements with lower electronegativity, such as sodium, have a weaker pull on electrons.

Understanding electronegativity differences helps predict whether a bond is likely to form as ionic or covalent.

Metal and Nonmetal Bonding

Metal and nonmetal bonding predominantly leads to the formation of ionic compounds. Metals, which are typically characterized by low electronegativity, tend to lose electrons easily, forming positively charged ions or cations. Nonmetals, with higher electronegativities, tend to gain these electrons, forming negatively charged ions or anions. This transfer of electrons from metals to nonmetals generates a strong electrostatic attraction between the oppositely charged ions, forming what we call ionic bonds. Consider sodium bromide (NaBr) as an example. Here, sodium (a metal) donates an electron to bromine (a nonmetal), resulting in an ionic bond.

Covalent Bonding

Covalent bonding occurs when two nonmetal atoms share electrons with each other. Unlike ionic bonds, where electrons are transferred, covalent bonds are formed by the sharing of electrons to achieve a full outer electron shell, resembling that of the closest noble gas. This type of bond is typically found in molecular compounds. For instance, methane (CH₄) is a covalent compound where carbon shares electrons with four hydrogen atoms. This sharing allows each hydrogen to achieve a helium-like electron configuration, and carbon achieves a stable arrangement similar to neon.

Ionic Bonding

Ionic bonding is a type of chemical bond where electrons are transferred from a metal to a nonmetal, creating ions that attract each other. The metal loses electrons to form a positive ion, while the nonmetal gains electrons to form a negative ion. This results in a strong electrical attraction between the ions, generating a stable ionic compound. Take cesium chloride (CsCl) as an example. Cesium donates an electron to chlorine, resulting in a cation (Cs⁺) and an anion (Cl⁻). The ionic bond forms due to the electrostatic attraction between these oppositely charged ions.

Compound Classification

Compounds can be broadly classified into ionic and molecular (covalent) compounds based on the types of elements involved and the bonding nature.

• Ionic compounds are generally formed between metals and nonmetals, with a transfer of electrons resulting in a crystalline lattice structure. Examples include sodium bromide (NaBr) and barium fluoride (BaF₂).
• Molecular compounds, typically formed between nonmetals, involve electron sharing and are often characterized by discrete molecules, such as methane (CH₄) and nitrogen trifluoride (NF₃).

Recognizing the nature of the constituent elements helps in predicting whether a compound is ionic or molecular, thus aiding in understanding their chemical behavior and properties.