Compounds and Bonding - AP Chemistry

Sulfate is a polyatomic ion that is composed of one sulfur atom and four oxygen atoms. The ion has a net charge of .

Since sodium ions have a charge of , we must use two atoms of sodium in order to result in a neutrally charged compound.

This makes the neutral chemical compound .

Since we know the percentages by mass, we can convert them into grams by imagining a 100-gram sample of the mystery compound. At that point, we can determine how many moles are present for each element:

By dividing each molar amount by the smallest molar amount (in this case 3.33), we can find the elemental ratios.

This means that the empirical formula for this compound is .

Since we were told that the molecular formula is six times as heavy as the empirical formula, we need to multiply each elemental amount in the empirical formula by six. After doing this, we find that the molecular formula is .

Carboxylic acids are formed by a carbon atom with a double bond to an oxygen atom, as well as an -oh substituent. This leaves one remaining bond for the carbon atom, allowing it to bind to a larger molecular component. The name for a carboxylic acid bound to a larger molecule is a "carboxyl group."

Carbonyl groups are formed when a carbon atom forms a doubl bond with an oxygen atom and any two other substituents. Carboxylic acids, aldehydes, ketones, esters, and amides are all carbonyl functional groups.

An ester is formed when a carbon forms a double bond with an oxygen and a single bond with a second oxygen atom. The second oxygen is generally incorporated into the backbone structure of the molecule, rather than as a single substituent to the carbon.

An ether is formed by an oxygen atom bound to two other atoms (usually carbons).

Ionic bonds generally occur between metal and nonmetal ions, while covalent bonds usually occur between two nonmetal atoms. The compounds containing sodium, iron, silver, calcium, and rubidium will all contain ionic bonds involving these elements.

The answer is the only answer without any metal atoms, indicating that the bonds in these molecules will be covalent.

Hydrogen bonds are present in molecules in which hydrogen atoms are bound to highly electronegative atoms, namely oxygen, fluorine, or nitrogen. These bonds are extremely polar, resulting in a partial positive charge on the hydrogen atoms and a partial negative charge on the more electronegative atom.

Of the given answer options, methane (), is the only one that does not involve a hydrogen atom bound to an oxygen, nitrogen, or fluorine. It cannot demonstrate hydrogen bonding.

Note that glucose (), as well as most other sugars, contain aldehyde or hydroxyl groups. These consist of -OH bonds, which allow for hydrogen bonding.

In an ammonia molecule, the nitrogen is bonded to three hydrogen atoms and also has a lone electron pair. This lone pair will repel the three hydrogens out of a planar orientation, which results in a trigonal pyramidal geometry.

Compounds with the general formula AX3 and one lone pair will be trigonal pyramidal.

Compounds with the general formula AX3 and no lone pairs will be trigonal planar.

Compounds with the general formula AX4 and no lone pairs will be tetrahedral.

Compounds with the general formula AX5 and no lone pairs will be trigonal bipyramidal.

Methane has a carbon atom attached to four hydrogen atoms. In order to be as far as possible from one another, the hydrogen atoms will orient themselves around the carbon in a tetrahedral geometry. Tetrahedral geometries have bond angles of between each constituent.

Generally, a central atom bound to two peripheral atoms will result in a linear shape, as exemplified by carbon dioxide. Exceptions come into play, however, with the introduction of lone pairs of electrons. These lone pairs carry a negative charge, pushing other atoms (and their negatively-charged electrons) farther away. In water, the central oxygen atom is bound to two hydrogen atoms and carries two lone pairs of electrons. As a result, the lone pairs propel the hydrogen atoms away from the linear structure, "bending" the molecule. The result is known as a bent molecular geometry, according to VSEPR theory. Any molecule in which the central atom is bound to two atoms and carries two lone pairs will result in a bent shape.

Carbon dioxide and cyanide are both linear. Ammonia is trigonal pyramidal. Methane is tetrahedral.

In the water molecule, there are four electron pairs. Two of them are bonded and two of them are lone pairs. This causes the water molecule to have a tetrahedral shape (it is important to note that it is a bent tetrahedral shape due to the two lone pairs).

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).

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.

We should first remember the difference between sulfate, sulfite, and sulfide. Sulfate is , sulfite is ` and sulfide is .

The only answer choices that could be right must have in them. We then need to see that barium usually has a charge of , as the periodic table shows us, and so we need a charge of to cancel that out. The answer is .

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

The molecule 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 prefix di- 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 .

is a molecular compound (a compound that contains two non-metals), so we must name it according to the rules for naming molecular compounds. These are different from the rules to name ionic compounds.

In molecular compounds we use prefixes (mono-, di-, tri- etc) at the beginning of each element to indicate the subscript for the element; however, we only use the prefix mono- for the second element in the compound. Mononitrogen dioxide is an incorrect answer choice because the compound name will never begin with mono-. We also need to change the ending of the last element in molecular compounds to -ide. Together, the name becomes "nitrogen dioxide."

Nitrate refers to the complex ion . Nitrogen oxide is simply . Nitrous acid is also known as hydrogen nitrite, and is formed from a hydrogen ion and a nitrite ion with an ionic bond: .

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: . Similarly, in carbon dioxide we put carbon first because it is farther to the left in the period: .

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

is a molecular compound, composed entirely of non-metallic elements with covalent bonds. Normally, these compounds follow a specific set of naming rules that would lead to this compound being called "nitrogen trihydride," however this particular compounds is an exception to normal naming rules.

is an example of a molecular compound that is given a non-systematic common name. The common name for is ammonia. Ammonium is incorrect, and refers to the complex ion .

Other exceptions to the naming rules include water () and methane ().

is an binary ionic compound because it contains one cation species and one anion species, connected by ionic bonds. Compounds with this structure should be named according to the rules for naming binary ionic compounds, which differ from the rules for naming molecular compounds. For these types of compounds the cation (usually a metal) should be listed first and the anion (non-metal) should be listed second with the suffix -_ide_added to the end.

Answer choices containing prefixes (mono-, di-, tri- etc) are incorrect because prefixes should only be used when naming molecular compounds.

Answer choices containing roman numerals are incorrect because roman numerals are only used to designate the charge of the cation when the cation is a transition metal, which are generally capable of multiple oxidation states and require the charge designation to differentiate. Magnesium is and alkaline earth metal, not a transition metal, and will always have a charge of positive two.

Using the proper naming conventions, refers to magnesium chloride.

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 and oxygen (O) has a charge of . 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.

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

Since beryllium is a cation metal and phosphorus is a anion non-metal, they can be combined to create an ionic compound.

In ionic compounds, the cation is always written before the anion in the formula so answer choices with phosphorus as the first element ( and ) are incorrect.

Ionic compounds must have a net charge of zero. Beryllium is an alkaline earth metal and has a charge of , since it is a member of group 2. Phosphorus has a charge of since it is a member of group 15. To create a molecule with a net charge of zero there must be three beryllium ions for every two phosphorus ions.

is not a correct answer choice because the net charge of the molecule does no equal zero.

is the balanced ionic formula for beryllium phosphate, but contains oxygen as well as beryllium and phosphorus.