Writing Formulas And Naming Compounds Answers

All High School Chemistry Resources

Which answer choice shows the correct chemical formula for barium sulfate?

Correct answer:

BaSO_4

Which of the following chemical compounds is written incorrectly?

Correct answer:

ClNa

Explanation:

Ionic chemical compounds are always named with the metal before the non-metal. The correct way to name sodium chloride would be NaCl , and not ClNa , because sodium is the metal and chloride is the non-metal.

All the other examples have the metal before the non-metal. The other answer choices correspond to potassium chloride, magnesium sulfate, hydrogen chloride (hydrochloric acid), and calcium fluoride.

Name the following compound:

$Fe_{2}O_{3}$

Possible Answers:

Iron(II) oxide

Iron oxide

Iron(III) oxide

Iron trioxide

Correct answer:

Iron(III) oxide

Explanation:

Because iron has multiple oxidation states, we need to follow the cation with the roman numeral that signifies how many electrons each iron ion has donated to oxygen. Since oxygen gains two electrons in order to satisfy its octet, the three oxygens will accept a total of six electrons from two iron atoms. This means that each iron must donate three electrons, so that each atom donates electrons equally. As a result, the name of the ionic compound is iron(III) oxide.

Another acceptable name for the compound would be ferric oxide. The term "ferric" refers to iron(III) and the term "ferrous" refers to iron (II).

Name the following compound:

$PF_{5}$

Possible Answers:

Monophosphorus pentafluoride

Phosphorus fluoride

Phosphorus tetrafluoride

Phosphorus pentafluoride

Correct answer:

Phosphorus pentafluoride

Explanation:

When naming covalent compounds, it is important to use a prefix before each element in order to designate how many atoms are in the compound. One key exception is when you only have one atom at the beginning of the compound (such as in this question). You will never start a covalent compound with "mono-". The prefix for five is "penta-", so the name of this covalent compound is phosphorus pentafluoride. The name indicates that there is one phosphorus atom bound to five fluorine atoms.

Which of the following molecular formulas is written incorrectly?

Correct answer:

Cl_2N_2

Explanation:

When naming molecular compounds, the rule is to put the element farthest to the left of the period table and closest to the bottom of the periodic table first.

For example, in sulfur dioxide, since sulfur and oxygen are both in group 6A, we put sulfur first since it is below oxygen in the group: SO_2 . Similarly, in carbon dioxide we put carbon first because it is farther to the left in the period: CO_2 .

Cl_2N_2 is written incorrectly because nitrogen is farther left on the periodic table than chlorine. Written correctly, this compound would be dinitrogen dichloride: N_2Cl_2 .

Choose the correct name for the following compound.

S_2Cl_2

Possible Answers:

Sulfur chlorate

Disulfur dichloride

Diasulfur diachloride

Sulfur dichloride

Sulfur chloride

Correct answer:

Disulfur dichloride

Explanation:

The molecule S_2Cl_2 is a molecular compound because it contains two non-metals; therefore, it contains no ionic bonds. We use prefixes to describe the subscript for each element in molecular compounds. The molecule in this question has a subscript of two for each of the elements, so the prefixdi- should be added to both sulfur and chlorine.

For molecular compounds, we change the ending of the final element to-ide, giving us the name "disulfur dichloride."

It is important to note that "chlorate" has a separate meaning, and refers to the complex ion ClO_3^- .

Choose the formula that corresponds to sodium oxide.

Correct answer:

$Na_{2}O$

Explanation:

We know that sodium oxide is a binary ionic compound because it contains one metal cation and one non-metal anion. To write the ionic formula we must write the cation first, followed by the anion, and make sure the net charge of the molecule is zero.

From the periodic table, we know that sodium (Na) has a charge of $\small +1$ and oxygen (O) has a charge of $\small -2$ . We know that the final charge on the molecule must be zero. To balance the charge, there must be two sodium atoms for every oxygen atom.

$Na^{_{^{+}}} + Na^{_{^{+}}} + O^{2-}= 0$

$Na_{2}O$

The other answer choices do not have a net charge of zero.

$Na_{2}O_{2}$

$Na^{_{^{+}}}+Na^{_{^{+}}}+O^{2-} +O^{2-}= -2$

$NaO_{2}$

$Na^{_{^{+}}}+O^{2-} +O^{2-}= -3$

NaO

$Na^{_{^{+}}} + O^{2-}= -1$

$Na_{3}O_{}2$

$Na^{_{^{+}}}+Na^{_{^{+}}}+Na^{_{^{+}}}+O^{2-} +O^{2-}= -1$

Which of the following ionic compounds is written incorrectly?

Correct answer:

LiSe

Explanation:

Ionic compounds are written with the cation (metal) first, followed by the anion (non-metal). All of the answer choices satisfy this requirement.

Next, we must look at the net charge on each molecule. All of the ionic compounds have a net charge of zero except for LiSe , which has a charge of $\small -1$ as written.

LiSe

$Li^{+}+Se^{2-}=-1$

The correct ionic formula for a compound containing these two elements is:

$Li_{2}Se$

$Li^{+}+Li^{+}+Se^{2-}=0$

Name the compound and determine the type of molecule.

${H_2}$

Possible Answers:

This molecule cannot exist

Hydrogen monohydride; binary ionic compound

Hydrogen; binary molecular compound

Hydrogen monohydride; diatomic molecular compound

Hydrogen; diatomic molecular compound

Correct answer:

Hydrogen; diatomic molecular compound

Explanation:

The given compound is the formula for gaseous hydrogen. Hydrogen atoms have only one valence electron and will form covalent bonds with other hydrogen atoms to fill the s orbital, generating a covalent bond. This tells us that it is a molecular bond, since no ionic bonds are present.

Binary compounds always contain two elements. This compound contains only one element, and cannot be considered binary. Instead, it is referred to as "diatomic," meaning that the molecule is composed of two atoms of the same element. Most diatomic molecules are gaseous, and include O_2 , N_2 , and Cl_2 (among others). The noble gases will not form diatomic particles.

Naming diatomic molecules is simple, since there is only one element involved. Most commonly, ${H_2}$ is simply named hydrogen or gaseous hydrogen. Keep this in mind when working with reactions. If a reaction occurs between nitrogen and oxygen, it is occurring between their diatomic molecules, not the individual atoms themselves.

Which of the following statements is false regarding the nomenclature and formulas of binary molecular compounds?

Possible Answers:

Molecular compounds can contain only non-metals

The element farthest to the left in the periodic table and closer to the top of a group appears first in the name and formula

The prefixmono- should only be used on the second element

The prefix hepta- means seven

The ending of the second element is replaced with the suffix -ide

Correct answer:

The element farthest to the left in the periodic table and closer to the top of a group appears first in the name and formula

Explanation:

Binary molecular compounds contain two non-metal elements joined by covalent bonds. Conventions for naming these compounds require that prefixes be used to denote the subscript of each element in the compound, telling the number of atoms in the name. The prefix for one, mono-, is only applied to the second element in the name, assuming that it has no subscript (one atom per molecule). The suffix -ide is attached to the second element in the compound to complete the name.

When determining which element should be first, you must reference the periodic table. Elements located more to the left and toward the bottom of the non-metals will appear first in the compound name. Carbon monoxide is a simple example of the leftmost element coming first, while bromine monochloride is an example of the bottommost element coming first.

The following is a list of prefixes used in naming molecular compounds:

One: mono-

Two: di-

Three: tri-

Four: tetra-

Five: penta-

Six: hexa-

Seven: hepta-

Eight: octa-

Nine: nona-

Ten: deca-

All High School Chemistry Resources

Report an issue with this question

If you've found an issue with this question, please let us know. With the help of the community we can continue to improve our educational resources.

DMCA Complaint

If you believe that content available by means of the Website (as defined in our Terms of Service) infringes one or more of your copyrights, please notify us by providing a written notice ("Infringement Notice") containing the information described below to the designated agent listed below. If Varsity Tutors takes action in response to an Infringement Notice, it will make a good faith attempt to contact the party that made such content available by means of the most recent email address, if any, provided by such party to Varsity Tutors.

Your Infringement Notice may be forwarded to the party that made the content available or to third parties such as ChillingEffects.org.

Please be advised that you will be liable for damages (including costs and attorneys' fees) if you materially misrepresent that a product or activity is infringing your copyrights. Thus, if you are not sure content located on or linked-to by the Website infringes your copyright, you should consider first contacting an attorney.

Please follow these steps to file a notice:

You must include the following:

A physical or electronic signature of the copyright owner or a person authorized to act on their behalf; An identification of the copyright claimed to have been infringed; A description of the nature and exact location of the content that you claim to infringe your copyright, in \ sufficient detail to permit Varsity Tutors to find and positively identify that content; for example we require a link to the specific question (not just the name of the question) that contains the content and a description of which specific portion of the question – an image, a link, the text, etc – your complaint refers to; Your name, address, telephone number and email address; and A statement by you: (a) that you believe in good faith that the use of the content that you claim to infringe your copyright is not authorized by law, or by the copyright owner or such owner's agent; (b) that all of the information contained in your Infringement Notice is accurate, and (c) under penalty of perjury, that you are either the copyright owner or a person authorized to act on their behalf.

Send your complaint to our designated agent at:

Charles Cohn Varsity Tutors LLC
101 S. Hanley Rd, Suite 300
St. Louis, MO 63105

Or fill out the form below: