Problem 114 - Chemistry The Molecular Science

Question

For each substance, (i) through (viii), (a) Write the correct formula. (b) Decide whether the substance is ionic or molecular. (i) \(\quad\) Sodium hypochlorite (ii) \(\quad\) Tetraphosphorus decaoxide (iii) \(\quad\) Potassium permanganate (iv) \(\quad\) Potassium dihydrogen phosphate (v) \(\quad\) Chlorine trifluoride (vi) \(\quad\) Boron tribromide (vii) \(\quad\) Calcium acetate (viii) Sodium sulfite

Step-by-Step Solution

Answer

(i) NaClO, ionic; (ii) P4O10, molecular; (iii) KMnO4, ionic; (iv) KH2PO4, ionic; (v) ClF3, molecular; (vi) BBr3, molecular; (vii) Ca(CH3COO)2, ionic; (viii) Na2SO3, ionic.

Step 1: Sodium Hypochlorite Formula

Sodium hypochlorite has sodium (Na) and hypochlorite (ClO) ions. The chemical formula for sodium hypochlorite is \( NaClO \).

Step 2: Sodium Hypochlorite Type

Since it is composed of a metal (sodium) and a polyatomic ion (hypochlorite), sodium hypochlorite is an ionic compound.

Step 3: Tetraphosphorus Decaoxide Formula

Tetraphosphorus decaoxide consists of phosphorus and oxygen with prefixes indicating the number of atoms: \( \text{P}_4\text{O}_{10} \).

Step 4: Tetraphosphorus Decaoxide Type

This compound is formed by non-metals (phosphorus and oxygen), making it a molecular compound.

Step 5: Potassium Permanganate Formula

Potassium permanganate is composed of potassium (K) and permanganate (MnO4) ions, with the formula \( KMnO_4 \).

Step 6: Potassium Permanganate Type

With a metal (potassium) and a polyatomic ion (permanganate), this is an ionic compound.

Step 7: Potassium Dihydrogen Phosphate Formula

Potassium dihydrogen phosphate has potassium (K), dihydrogen (H2), and phosphate (PO4) ions, leading to the formula \( KH_2PO_4 \).

Step 8: Potassium Dihydrogen Phosphate Type

As it contains a metal (potassium) with other ions, potassium dihydrogen phosphate is ionic.

Step 9: Chlorine Trifluoride Formula

Chlorine trifluoride is composed of chlorine and three fluorine atoms, written as \( ClF_3 \).

Step 10: Chlorine Trifluoride Type

This compound consists of two non-metals, classifying it as a molecular compound.

Step 11: Boron Tribromide Formula

Boron tribromide consists of boron and three bromine atoms, leading to the formula \( BBr_3 \).

Step 12: Boron Tribromide Type

With only non-metal elements, boron tribromide is a molecular compound.

Step 13: Calcium Acetate Formula

Calcium acetate is made from calcium (Ca) and acetate (CH3COO) ions, with the formula \( Ca(CH_3COO)_2 \).

Step 14: Calcium Acetate Type

Comprising a metal (calcium) and an organic ion (acetate), calcium acetate is ionic.

Step 15: Sodium Sulfite Formula

Sodium sulfite involves sodium (Na) and sulfite (SO3) ions, giving the formula \( Na_2SO_3 \).

Step 16: Sodium Sulfite Type

Consisting of a metal (sodium) and a polyatomic ion (sulfite), sodium sulfite is ionic.

Key Concepts

Molecular Compounds

Molecular compounds, also known as covalent compounds, are formed when two or more non-metal elements share electrons, creating a stable bond. This sharing of electrons allows each atom to achieve a full outer shell, mimicking the electron configuration of noble gases. Due to the covalent bonding, molecular compounds have some distinct properties. They typically have lower melting and boiling points compared to ionic compounds.
They are often gases or liquids at room temperature, but they can also be solids. Another characteristic property of molecular compounds is their poor electrical conductivity in their pure form.The naming of molecular compounds relies on using prefixes that signify the amount of each atom present in the compound:

• "Mono-" for one
• "Di-" for two
• "Tri-" for three
• "Tetra-" for four
• "Penta-" for five
• ...and so on.

These prefixes are essential when writing formulas, as seen in compounds like tetraphosphorus decaoxide (\( \text{P}_4\text{O}_{10} \)) and chlorine trifluoride (\( ClF_3 \)).Recognizing these compounds is key to understanding their chemical behavior and reactions.

Ionic Compounds

Ionic compounds are the result of the electrostatic attraction between oppositely charged ions. Typically, these ions are a metal losing electrons to become positively charged cations, and a non-metal gaining electrons to form negatively charged anions.
Because of this strong attraction, ionic compounds generally have high melting and boiling points, and they tend to be solid at room temperature. Additionally, they are known for conducting electricity when dissolved in water or molten, due to the free movement of ions.The composition of ionic compounds is expressed as a simple ratio of each type of ion so that the overall charge is neutral. For example, sodium hypochlorite (\( NaClO \)) and calcium acetate (\( Ca(CH_3COO)_2 \)) have well-defined stoichiometry balanced for neutrality.
Recognizing these compounds can often be achieved by noting the presence of at least one metal and a polyatomic ion or a non-metal counterion.Examples include substances like potassium permanganate (\( KMnO_4 \)), where potassium (a metal) binds with permanganate ions, and sodium sulfite (\( Na_2SO_3 \)), which combines sodium with sulfite ions.

Chemical Formulas

Chemical formulas are a succinct way to represent the chemical composition of a compound. They involve using chemical symbols, numbers, and sometimes additional subscript numbers to convey information about each element's presence. For molecular compounds, the chemical formula reflects the actual number of atoms of each non-metal element per molecule.
This is very useful in compounds like boron tribromide, represented as \( BBr_3 \).In the case of ionic compounds, the chemical formula reflects the simplest whole number ratio of ions that results in an overall neutral charge. This is seen with compounds such as potassium dihydrogen phosphate (\( KH_2PO_4 \)) and sodium sulfite (\( Na_2SO_3 \)).The formulation of both molecular and ionic compounds relies on recognizing both elemental symbols and understanding the common ions and their charges. Through these formulas, chemists and students alike can derive rich information about the compound, including its constituent atoms and the proportion of each. Understanding chemical formulas is crucial for studying chemical reactions, as they provide a basis for balancing equations and predicting reaction outcomes.