Question

Write the formulas for the following compounds: (a) rubidium nitrite, (b) potassium sulfide, (c) sodium hydrogen sulfide, (d) magnesium phosphate, (e) calcium hydrogen phosphate, (f) lead(II) carbonate, (g) tin(II) fluoride, (h) ammonium sulfate, (i) silver perchlorate, (j) boron trichloride.

Short answer

(a) RbNO₂, (b) K₂S, (c) NaHS, (d) Mg₃(PO₄)₂, (e) CaHPO₄, (f) PbCO₃, (g) SnF₂, (h) (NH₄)₂SO₄, (i) AgClO₄, (j) BCl₃.

Step-by-step solution

Understand the Compound Composition

To write the formula for a compound, it's necessary to understand the ions or atoms it consists of. Each name specifies the elements and their ratios in the compound, often involving cations (positively charged ions) and anions (negatively charged ions).

Write the Formula for (a) Rubidium Nitrite

Rubidium (Rb) is an alkali metal, so it forms a +1 cation: Rb⁺. Nitrite is a polyatomic ion with the formula NO₂⁻. Combining these gives the formula: RbNO₂.

Write the Formula for (b) Potassium Sulfide

Potassium (K) forms a +1 cation: K⁺. Sulfide is a -2 anion: S²⁻. We need two potassium ions to balance one sulfide ion, leading to the formula: K₂S.

Write the Formula for (c) Sodium Hydrogen Sulfide

Sodium (Na) forms a +1 cation: Na⁺. Hydrogen sulfide involves the HS⁻ ion. Combine one Na⁺ with one HS⁻ to get: NaHS.

Write the Formula for (d) Magnesium Phosphate

Magnesium (Mg) forms a +2 cation: Mg²⁺. Phosphate is a polyatomic ion with the formula PO₄³⁻. Three magnesium ions pair with two phosphate ions, resulting in: Mg₃(PO₄)₂.

Write the Formula for (e) Calcium Hydrogen Phosphate

Calcium (Ca) forms a +2 cation: Ca²⁺. Hydrogen phosphate is HPO₄²⁻. One calcium ion pairs with one hydrogen phosphate ion: CaHPO₄.

Write the Formula for (f) Lead(II) Carbonate

Lead(II) indicates Pb²⁺. Carbonate is CO₃²⁻. One lead(II) ion balances one carbonate ion, forming PbCO₃.

Write the Formula for (g) Tin(II) Fluoride

Tin(II) indicates Sn²⁺. Fluoride is F⁻. Two fluoride ions balance one tin(II) ion, creating SnF₂.

Write the Formula for (h) Ammonium Sulfate

Ammonium is a polyatomic ion NH₄⁺. Sulfate is SO₄²⁻. Two ammonium ions pair with one sulfate ion to balance the charges: (NH₄)₂SO₄.

Write the Formula for (i) Silver Perchlorate

Silver forms a +1 cation: Ag⁺. Perchlorate is ClO₄⁻. One silver ion balances one perchlorate ion, resulting in AgClO₄.

Write the Formula for (j) Boron Trichloride

Boron (B) forms compounds by sharing electrons. Trichloride refers to three chlorine atoms. Together, they form BCl₃.

Key concepts

Ionic Compounds

Ionic compounds are formed by the combination of cations and anions, which are positively and negatively charged ions, respectively. These compounds are typically composed of metals and non-metals. When cations and anions come together, they do so in a way that balances out their charges, creating an electrically neutral compound. To achieve this neutrality, the total positive charge must equal the total negative charge.

• Examples include sodium chloride ( ext{Na}^+ ext{Cl}^-), magnesium oxide ( ext{Mg}^{2+} ext{O}^{2-}), and calcium carbonate ( ext{Ca}^{2+} ext{CO}_3^{2-}).
• The forces holding these ions together are strong electrostatic forces called ionic bonds.
• Properties of these compounds include high melting and boiling points due to the strong bonds.

Recognizing the type of ions involved and their charges is crucial for determining the correct formula for ionic compounds.

Cations and Anions

Cations and anions are essential components of ionic compounds, with each playing unique roles based on their charges. Cations are positively charged ions that usually form from metallic elements. When metals lose electrons, they become cations due to the excess positive charge from protons.

• For example, sodium ( ext{Na}^+) loses one electron to become a cation, and magnesium ( ext{Mg}^{2+}) loses two electrons.

Anions are negatively charged ions formed when non-metals gain electrons. The extra electrons add negative charge to the atom or molecule.

• For example, chloride ( ext{Cl}^-) gains one electron, and sulfide ( ext{S}^{2-}) gains two electrons.

Understanding which are cations and anions in a compound is vital for constructing the accurate chemical formula.

Polyatomic Ions

Polyatomic ions are ions composed of more than one atom. These ions act as a single charged entity, just like a simple ion. They are an important part of many ionic compounds, and recognizing them can simplify the process of writing chemical formulas. Polyatomic ions maintain their charge even when they form compounds and usually require memorization for proper identification.

• Common polyatomic ions include nitrate ( ext{NO}_3^-), sulfate ( ext{SO}_4^{2-}), and phosphate ( ext{PO}_4^{3-}).
• Ammonium ( ext{NH}_4^+) is a frequently encountered polyatomic cation.
• Formulas can include parentheses to denote the number of polyatomic ions as needed, like in ammonium sulfate ext{(NH}_4)_2 ext{SO}_4.

Being able to identify polyatomic ions helps in balancing the overall charges when forming compounds.

Charge Balancing

Charge balancing is a necessary step in writing the formulas of ionic compounds. It ensures that the total positive charge equals the total negative charge, resulting in a neutral compound. This process often involves determining the ratio of each ion required to balance charges.

• If calcium ( ext{Ca}^{2+}) combines with phosphate ( ext{PO}_4^{3-}), we need three calcium ions for every two phosphate ions to balance the charge, leading to the formula ext{Ca}_3( ext{PO}_4)_2.
• In the case of creating potassium sulfide, two potassium ions ( ext{K}^+) are required to balance one sulfide ion ( ext{S}^{2-}), resulting in ext{K}_2 ext{S}.
• Understanding the valency and common charges of ions aids in predicting how many of each ion will be needed.

Correctly balancing these charges is paramount to writing the correct chemical formulas for ionic compounds and predicting their compositions.