Problem 65 - Chemistry: The Central Science

Question

Predict whether each of the following compounds is molecular or ionic: (a) \(\mathrm{B}_{2} \mathrm{H}_{6}\), (b) \(\mathrm{CH}_{3} \mathrm{OH}\), (c) \(\mathrm{LiNO}_{3}\), (d) \(\mathrm{Sc}_{2} \mathrm{O}_{3}\), (e) \(\mathrm{CsBr}\), (f) \(\mathrm{NOCl}\), (g) \(\mathrm{NF}_{3}\), (h) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\).

Step-by-Step Solution

Answer

(a) Molecular, (b) Molecular, (c) Ionic, (d) Ionic, (e) Ionic, (f) Molecular, (g) Molecular, (h) Ionic.

Step 1: Compound a: \(\mathrm{B}_{2}\mathrm{H}_{6}\)

Compound a is formed between two non-metals, boron (B) and hydrogen (H), which means it is likely to be a molecular compound.

Step 2: Compound b: \(\mathrm{CH}_{3}\mathrm{OH}\)

Compound b consists of carbon (C), hydrogen (H), and oxygen (O), all of which are non-metals. Therefore, this compound is molecular.

Step 3: Compound c: \(\mathrm{LiNO}_{3}\)

Compound c is formed between lithium (Li), a metal, and a group of non-metals (N and O). As such, this compound is ionic.

Step 4: Compound d: \(\mathrm{Sc}_{2}\mathrm{O}_{3}\)

This compound is composed of scandium (Sc), a metal, and oxygen (O), a non-metal. Thus, it is an ionic compound.

Step 5: Compound e: \(\mathrm{CsBr}\)

Compound e is formed between cesium (Cs), a metal, and bromine (Br), a non-metal. This indicates that the compound is ionic.

Step 6: Compound f: \(\mathrm{NOCl}\)

All elements in compound f - nitrogen (N), oxygen (O), and chlorine (Cl) - are non-metals. As a result, the compound is molecular.

Step 7: Compound g: \(\mathrm{NF}_{3}\)

Compound g consists of nitrogen (N) and fluorine (F), both of which are non-metals, making it a molecular compound.

Step 8: Compound h: \(\mathrm{Ag}_{2}\mathrm{SO}_{4}\)

This compound is composed of silver (Ag), a metal, and a group of non-metals (S and O). Therefore, it is an ionic compound.

Key Concepts

Chemical Bonding

Chemical bonding is the process by which atoms combine to form compounds. The nature of the bond formed between atoms is crucial in determining the properties of the resulting compound. There are two predominant types of chemical bonds: ionic and covalent.

Ionic bonds occur between a metal and a non-metal. These bonds involve the transfer of electrons from the metal to the non-metal, resulting in the formation of positively charged metal cations and negatively charged non-metal anions. An example from our exercise is \( \mathrm{LiNO}_{3} \), where lithium (Li) donates an electron to the nitrate group, forming an ionic bond.

Covalent bonds, on the other hand, happen between non-metals and involve the sharing of electron pairs. \( \mathrm{B}_{2}\mathrm{H}_{6} \) is a representative example. The boron (B) and hydrogen (H) atoms share electrons, creating a strong bond and a molecular compound.

Understanding these bonding types helps in predicting properties like melting and boiling points, solubility, and electrical conductivity of compounds.

Compound Classification

Compounds are classified based on the types of elements they contain and the nature of the bond that holds them together. Molecular compounds are composed of non-metals and held together by covalent bonds, as seen in \( \mathrm{CH}_{3} \mathrm{OH} \) where carbon, hydrogen, and oxygen share electrons.

Molecular Compounds

Molecular compounds typically have low melting and boiling points and are often found in gaseous or liquid states at room temperature. They can be polar or non-polar, determining their solubility in various solvents.

Ionic Compounds

Ionic compounds usually consist of a metal and a non-metal. They tend to have high melting and boiling points and form crystalline solids, such as \( \mathrm{CsBr} \). They readily dissolve in water and conduct electricity when melted or dissolved, due to the movement of ions.

The correct classification of compounds aids in predicting their reactivity and suitability for specific applications in industry and research.

Metal and Non-metal Chemistry

The periodic table separates elements into metals and non-metals, which differ significantly in their chemical properties. Metals, like scandium (Sc) in \( \mathrm{Sc}_{2}\mathrm{O}_{3} \), typically lose electrons to form positive ions. They are often shiny, malleable, ductile, and good conductors of heat and electricity. This tendency to lose electrons makes metals reactive, especially with non-metals, leading to the formation of ionic compounds.

Non-metals, such as nitrogen (N) in \( \mathrm{NOCl} \), tend to gain or share electrons to form negative ions or neutral molecules. They are usually not lustrous and are poor conductors of heat and electricity, reflecting their greater electronegativity compared to metals. Non-metals combine with each other to form covalent bonds, resulting in molecular compounds.

Understanding the chemistry of metals and non-metals is vital for grasping how substances interact. This knowledge also explains the diverse range of material properties we observe, from the flexibility of plastic to the conductivity of copper wires.