Problem 120 - Chemistry and Chemical Reactivity

Question

Ionic and molecular compounds of the halogens. (a) What are the names of BaF \(_{2}, \mathrm{SiCl}_{4}\), and \(\mathrm{NiBr}_{2} ?\) (b) Which of the compounds in part (a) are ionic, and which are molecular? (c) Which has the largest mass, 0.50 mol of BaF \(_{2}\) 0.50 mol of \(\mathrm{SiCl}_{4},\) or 1.0 mol of \(\mathrm{NiBr}_{2} ?\)

Step-by-Step Solution

Answer

BaF2: Barium fluoride; SiCl4: Silicon tetrachloride; NiBr2: Nickel(II) bromide. Ionic: BaF2, NiBr2; Molecular: SiCl4. 1.0 mol of NiBr2 has the largest mass.

Step 1: Naming BaF2

BaFequals: Barium fluoride. \(\text{Ba}\) is barium, a metal, and \(\text{F}\) is fluoride, the ion form of fluorine.

Step 2: Naming SiCl4

\(\text{SiCl}_4\) equals Silicon tetrachloride. \(\text{Si}\) represents silicon, and \(\text{Cl}_4\) indicates four chlorine atoms. The prefix "tetra-" is used because there are four chlorine atoms.

Step 3: Naming NiBr2

\(\text{NiBr}_2\) equals Nickel(II) bromide. The \(\text{Ni}^{2+}\) indicates that nickel has a +2 charge, and bromide is the ion form of bromine.

Step 4: Identifying Ionic and Molecular Compounds

Ionic compounds form between metals and nonmetals. \(\text{BaF}_2\) and \(\text{NiBr}_2\) are ionic because they consist of a metal and a nonmetal. \(\text{SiCl}_4\) is a molecular compound as it involves only nonmetals.

Step 5: Calculating Molar Mass

Calculate molar masses:- \(\text{BaF}_2\): \(\text{Ba} = 137.33\), \(\text{F} = 18.998 \times 2 = 37.996\), total = 175.326 \text{g/mol}- \(\text{SiCl}_4\): \(\text{Si} = 28.085\), \(\text{Cl} = 35.453 \times 4 = 141.812\), total = 169.897 \text{g/mol}- \(\text{NiBr}_2\): \(\text{Ni} = 58.693\), \(\text{Br} = 79.904 \times 2 = 159.808\), total = 218.501 \text{g/mol}

Step 6: Compare the Masses

Calculate the mass for given moles. - 0.50 mol \(\text{BaF}_2\): \(0.50 \times 175.326 = 87.663\) grams- 0.50 mol \(\text{SiCl}_4\): \(0.50 \times 169.897 = 84.9485\) grams- 1.0 mol \(\text{NiBr}_2\): \(1.0 \times 218.501 = 218.501\) gramsThe largest mass is from 1.0 mol of \(\text{NiBr}_2\).

Key Concepts

Halogens

The halogens represent Group 17 on the periodic table. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are known for their high reactivity due to having seven electrons in their valence shell.

• Halogens often form salts when combined with metals.
• Typically found as ions, such as fluoride (F⁻), chloride (Cl⁻), and bromide (Br⁻), when paired with positive metal ions.

In chemical nomenclature, the presence of halogens in a compound often results in the use of prefixes or suffixes, such as the addition of "ide" to the halogen's name, indicating it is an anion (like in fluoride or chloride). Their strong electronegativity makes them effective in forming ionic compounds with metals, highlighting their versatility and importance in chemistry.

Molar Mass Calculation

Calculating the molar mass of a compound is important for determining the weight of a substance in a chemical reaction.

• Begin by identifying each element in the compound and its quantity based on the chemical formula.
• Find the atomic weight of each element (listed on the periodic table).
• Multiply the atomic weight by the number of atoms present in the compound.

The sum of all these products gives the total molar mass of the compound. For example:- For BaF\(_2\), compute: Ba with a molar mass of 137.33 g/mol and F with a molar mass of 18.998 g/mol times 2. The total equals 175.326 g/mol.- Practice by comparing between compounds and determining which has the highest mass given different molar quantities as seen when comparing BaF\(_2\), SiCl\(_4\), and NiBr\(_2\), where NiBr\(_2\) has a significantly higher molar mass.

Chemical Nomenclature

Chemical nomenclature is the systematic naming of chemical compounds, providing a standard way to communicate complex information easily.

• Ionic compounds are named by stating the cation (metal) first, followed by the anion (non-metal) with an "ide" suffix.
• In transition metals, Roman numerals indicate the ion charge, such as Nickel(II) in NiBr\(_2\).
• Molecular compounds use prefixes to indicate the number of each type of atom.

For example, in SiCl\(_4\) (Silicon tetrachloride), "tetra" indicates four chlorine atoms bonded to silicon. Clear and consistent naming allows chemists to understand the composition and structure of compounds without ambiguity, crucial for accurate communication and understanding in scientific contexts.