Question

Write the formula for each of the following compounds: a. chromium(VI) oxide b. disulfur dichloride c. nickel(II) fluoride d. potassium hydrogen phosphate e. aluminum nitride f. ammonia g. manganese(IV) sulfide h. sodium dichromate i. ammonium sulfite J. carbon tetraiodide

Short answer

a. \(CrO_3\) b. \(S_2Cl_2\) c. \(NiF_2\) d. \(K_2HPO_4\) e. \(AlN\) f. \(NH_3\) g. \(MnS_2\) h. \(Na_2Cr_2O_7\) i. \((NH_4)_2SO_3\) j. \(CI_4\)

Step-by-step solution

a. chromium(VI) oxide

Chromium has a valency of +6 (as given by the roman numeral VI), and oxygen has a valency of -2. We need to balance the charges: Chromium: Cr (+6) Oxygen: O (-2) To balance these charges, we need three oxygen atoms for each chromium atom: Cr2O6 -> Simplify -> CrO3 The formula for chromium(VI) oxide is CrO3.

b. disulfur dichloride

The prefixes "di" mean "two," so we have two sulfur atoms and two chlorine atoms: Sulfur: S2 Chlorine: Cl2 The formula for disulfur dichloride is S2Cl2.

c. nickel(II) fluoride

Nickel has a valency of +2 (as given by the roman numeral II), and fluoride has a valency of -1: Nickel: Ni (+2) Fluoride: F (-1) To balance these charges, we need two fluoride atoms for each nickel atom: NiF2 The formula for nickel(II) fluoride is NiF2.

d. potassium hydrogen phosphate

Potassium has a valency of +1, hydrogen has a valency of +1, and phosphate has a valency of -3: Potassium: K (+1) Hydrogen: H (+1) Phosphate: PO4 (-3) To balance these charges, we need two potassium atoms, one hydrogen atom, and one phosphate ion: K2HPO4 The formula for potassium hydrogen phosphate is K2HPO4.

e. aluminum nitride

Aluminum has a valency of +3, and nitrogen has a valency of -3: Aluminum: Al (+3) Nitrogen: N (-3) Since their valencies are equal and opposite, we need one aluminum atom and one nitrogen atom: AlN The formula for aluminum nitride is AlN.

f. ammonia

Ammonia consists of one nitrogen atom and three hydrogen atoms: N: Nitrogen H3: Three Hydrogen atoms The formula for ammonia is NH3.

g. manganese(IV) sulfide

Manganese has a valency of +4 (as given by the roman numeral IV), and sulfide has a valency of -2: Manganese: Mn (+4) Sulfide: S (-2) To balance these charges, we need two sulfide atoms for each manganese atom: MnS2 The formula for manganese(IV) sulfide is MnS2.

h. sodium dichromate

Sodium has a valency of +1, and dichromate has a valency of -2: Sodium: Na (+1) Dichromate: Cr2O7 (-2) To balance these charges, we need two sodium atoms for each dichromate ion: Na2Cr2O7 The formula for sodium dichromate is Na2Cr2O7.

i. ammonium sulfite

Ammonium has a valency of +1, and sulfite has a valency of -2: Ammonium: NH4 (+1) Sulfite: SO3 (-2) To balance these charges, we need two ammonium ions for each sulfite ion: (NH4)2SO3 The formula for ammonium sulfite is (NH4)2SO3.

j. carbon tetraiodide

Carbon has a valency of +4, and the prefix "tetra" means "four," indicating four iodine atoms: Carbon: C (+4) Iodine: I4 (-4) Since the valencies match, we just combine them into a single formula: CI4 The formula for carbon tetraiodide is CI4.

Key concepts

Valency and Chemical Bonding

Understanding the valency of an element is crucial to forming chemical compounds. Valency reflects an element's capacity to bond with other elements; it indicates the number of electrons an atom will gain, lose, or share to achieve a full outer shell, resembling the nearest noble gas configuration.

The exercise on writing chemical formulas begins by identifying the valency of each element. For instance, in chromium(VI) oxide (CrO3), chromium has a valency of +6, meaning it can accept or share six electrons. Oxygen, on the other hand, typically has a valency of -2. By balancing these valencies, we can deduce that one chromium atom will bond with three oxygen atoms to form a stable compound.

Chemical Bonding Basics

There are different types of chemical bonds, primarily ionic and covalent. Ionic bonds occur between metals and nonmetals when valence electrons are transferred from one atom to another, creating oppositely charged ions that attract one another. Covalent bonds involve sharing of electrons between nonmetals. Comprehending the type of bond helps in predicting the resulting compound's properties and formula structure.

Naming Chemical Compounds

Properly naming compounds is fundamental for clear communication in chemistry. The name can provide vital information about the elements present and their quantities. We use specific rules for ionic and molecular (covalent) compounds. For instance, ionic compounds like nickel(II) fluoride (NiF2) are named by stating the metal first followed by the non-metal with an '-ide' suffix, while the oxidation state of the metal is given in parentheses if the metal has more than one common charge.

Prefixes and Oxidation States

In naming molecular compounds such as disulfur dichloride (S2Cl2), prefixes like 'di-' indicate the number of atoms. Polyatomic ions like ammonium or sulfate have special names that must be memorized, as they behave like single units during bonding. While writing names from formulas or formulas from names, it's important to consider these conventions and the overall context of the compound's structure.

Polyatomic Ions

Polyatomic ions are groups of atoms that behave as a single ion, and they have a charge resulting from the loss or gain of electrons. Common examples from the exercises include the phosphate ion (\(PO_4^{3-}\)) in potassium hydrogen phosphate (K2HPO4) and the dichromate ion (\(Cr_2O_7^{2-}\)) in sodium dichromate (Na2Cr2O7).

Understanding the composition and charge of polyatomic ions is vital when writing chemical formulas. Because they are treated as a single entity, the overall valency of the ion must be balanced with the counterion(s). For example, with ammonium sulfite ((NH4)2SO3), two ammonium ions (NH4+) balance out the charge of one sulfite ion (SO3^{2-}). Memorizing the most common polyatomic ions and their charges is a helpful strategy for students tackling chemical formula writing.