Question

Write the formulas and names of the following: (a) An ionic compound whose cation is a transition metal with 25 protons and 22 electrons and whose anion is an oxoanion of nitrogen with two oxygen atoms. (b) A molecule made up of a metalloid in Group 13 and three atoms of a halogen in period 2 . (c) An ionic compound made up of an alkaline earth with 20 protons, and an anion with one hydrogen atom, a carbon atom, and 3 oxygen atoms.

Short answer

Question: Identify and name the compounds described in the step-by-step solution. Answer: The compounds are (a) manganese(III) nitrite with the formula Mn(NO₂)₃, (b) boron trifluoride with the formula BF₃, and (c) calcium bicarbonate with the formula Ca(HCO₃)₂.

Step-by-step solution

(a) Find the cation element

By looking at the periodic table, the element with 25 protons has an atomic number of 25, which corresponds to manganese (Mn). With 22 electrons instead of 25, there will be a charge of +3. Thus, the cation is Mn⁺³.

(a) Identify the oxoanion of nitrogen

An oxoanion is a polyatomic ion that contains oxygen. In this case, we have nitrogen with two oxygen atoms. The most common oxoanion of nitrogen with two oxygen atoms is NO₂⁻, which is called nitrite.

(a) Write the formula and name of the ionic compound

To form a neutral compound, we'll need 3 nitrite ions for every manganese(III) ion. The chemical formula will be Mn(NO₂)₃, and the name of the compound is manganese(III) nitrite.

(b) Identify the metalloid in Group 13

By referring to the periodic table, we can find that the metalloid in Group 13 is boron (B).

(b) Identify the halogen in period 2

Again, using the periodic table, the halogen in period 2 is fluorine (F).

(b) Write the formula and name of the molecule

The molecule is made up of boron and three fluorine atoms, so the chemical formula is BF₃. The name of the molecule is boron trifluoride.

(c) Identify the alkaline earth element with 20 protons

Using the number of protons and referencing the periodic table, the alkaline earth element with 20 protons is calcium (Ca).

(c) Identify the anion with one hydrogen, one carbon, and three oxygen atoms

The polyatomic anion containing one hydrogen, one carbon, and three oxygen atoms is HCO₃⁻, which is called hydrogen carbonate or bicarbonate.

(c) Write the formula and name of the ionic compound

To form a neutral compound, we need one calcium ion and two bicarbonate ions, as calcium has a +2 charge and bicarbonate has a -1 charge. The chemical formula will be Ca(HCO₃)₂, and the name of the compound is calcium bicarbonate.

Key concepts

Transition Metal Cations

Transition metal cations are positively charged ions formed when atoms of transition metals lose electrons. Transition metals are those elements found in the d-block of the periodic table and they often have multiple oxidation states because they can lose varying numbers of d-electrons.

In our example, manganese (Mn) is the transition metal in question. It has 25 protons and ordinarily would have 25 electrons if it was neutral. However, as it has only 22 electrons, it has lost 3 electrons. This loss of electrons results in a positively charged cation, specifically Mn³⁺. Manganese with a +3 charge is denoted as manganese(III), indicating its oxidation state. Understanding the oxidation state is crucial because it determines how these metals will combine with other ions to form compounds.

Oxoanion Identification

Oxoanions are negatively charged polyatomic ions that contain one or more oxygen atoms bonded to a central atom, which is usually a nonmetal. The name of an oxoanion often ends in '-ate' or '-ite,' with '-ate' used for the ion with more oxygen atoms and '-ite' for the one with fewer.

In step 2 of the solution, we identify an oxoanion made of nitrogen and oxygen. Nitrogen can form several oxoanions, but with two oxygen atoms, the ion is the nitrite ion, NO₂⁻. Identifying these ions correctly is important in compound naming and for predicting the reactions they might undergo. For instance, if nitrogen had been bonded with three oxygen atoms, the ion would have been nitrate (NO₃⁻) instead.

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded, or of a metal complex that acts as a single unit with a net charge because the number of electrons lost or gained is not balanced by the number of protons.

These ions are ubiquitous in chemical compounds, and their naming is based on the atoms present and the overall charge. For example, in both step 2 with nitrite (NO₂⁻) and step 8 with hydrogen carbonate (HCO₃⁻), we see how the combination of different nonmetals with oxygen results in polyatomic ions with distinct properties. Recognizing various polyatomic ions is key in understanding chemical formulas and in balancing chemical equations.

Molecular Formulas

Molecular formulas provide vital information about the composition of a compound. They show the types and numbers of atoms that are combined in a single molecule of a compound. In our exercises, we see different types of molecular formulas: ionic compounds such as Mn(NO₂)₃ and Ca(HCO₃)₂, and covalent compounds like BF₃.

Molecular formulas are determined based on the valency of each atom or ion so that the overall charge of the compound is neutral. For instance, Mn³⁺ requires three nitrite ions (NO₂⁻) to achieve neutrality, which is reflected in the chemical formula Mn(NO₂)₃. Understanding how to read and write molecular formulas is fundamental for students to not only name compounds correctly but also to anticipate their physical and chemical properties.