Elements and Compounds - 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).

Isotopes are variations of an element that differ by the number of neutrons in the nucleus. Neutrons are neutrally charged, so adding or removing them from a nucleus does not alter the charge of the atom. The atomic number is the number of protons in an atom, and the mass number is the sum of both protons and neutrons in the nucleus. As a result, the mass number will change by adding a neutron.

The number of protons is equal to the atomic number of the element. Adding or subtracting protons will change the element's identity. Ions can be created by changing the number of electrons and isotopes can be created by changing the number neutrons, but changing the number of protons changes the element.

Ions are atoms that have gained or lost electrons. This results in an atom with a charge. Atoms with a neutral charge have an equal number of protons and electrons. Changing the electron number will result in a charge on the atom.

For example, adding an electron to chlorine creates a chlorine anion.

Carbon is an element with six protons (atomic number six), and most commonly has six neutrons. This brings the total mass of carbon to twelve atomic mass units (12amu). There are isotopes of carbon with seven or eight neutrons, which are radioactive. These isotopes correspond to carbon-13 and carbon-14. The true atomic mass of carbon on the periodic table is 12.011amu, accounting for small contributions by these heavier isotopes.

Carbon-6, cabron-7, carbon-8, and carbon-9 imply isotopes with zero, one, two, and three neutrons respectively. Though these isotopes could theoretically exist, they would be extremely unstable and do not occur in nature.

Two atoms are isoelectric if they each have the same number of electrons. In its ground state, bromine has 35 electrons, equal to the number of protons in order to have a neutral atom. In order to become a bromide ion, the bromine atom must gain one electron. This gives it a charge of negative one, but allows it to satisfy the octet rule, making it a very stable ion. With the ionization, the atom now has 36 electrons.

Krypton has atomic number 36, meaning that it will also have 36 electrons in its ground state.

Two atoms are isoelectric if they each have the same number of electrons. In its ground state, oxygen has 8 electrons, equal to the number of protons in order to have a neutral atom. In order to become a stable ion, the oxygen atom must gain two electrons. This gives it a charge of negative two, but allows it to satisfy the octet rule, making it a very stable ion. With the ionization, the atom now has 10 electrons.

Neon has atomic number 10, meaning that it will also have 10 electrons in its ground state.

Two atoms are isoelectric if they each have the same number of electrons. Ions of an element will vary in the number of electrons, but isotopes will vary in the number of neutrons only. In its ground state, fluorine has 9 electrons, equal to the number of protons in order to have a neutral atom. Any ground state isotopes of fluorine will also have 9 electrons, making them isoelectric.

Isoelectronic atoms are atoms or ions that contain the same number of total electrons. is not isoelectronic with the rest of the ions and atoms listed because it contains a total of ten electrons, while the rest in the series contain thirty-six.

Positively charged ions (cations) are formed when electrons are removed from the outer shell of the atom. Removing a negatively charged electron gives the ion a positive charge. For example, the element rubidium, , in its ground state contains thirty-seven electrons. The ion contains one less, thirty-six, making it isoelectronic with krypton and the other ions and atoms in the series.

Negatively charge ions (anions) are formed when electrons are added to the outer shell of the atom. Adding a negatively charged electron gives the ion a negative charge. For example, ground state selenium, , contains thirty-four electrons. The ion , has two added electrons giving it a total of thirty-six electrons. The ion is isoelectronic with the other ions and atoms in the series.

The general isotopic notation is as follows: , where is the mass number, which is equal to the number of neutrons plus protons, and is the atomic number, which is equal to the number of protons. We know that the atomic number determines the identity of an element, thus an atom with 19 protons must be potassium . Following the isotopic notation mentioned above, our mass number is 39.

The general isotopic notation is as follows: , where is the mass number, which is equal to the number of neutrons plus protons, and is the atomic number, which is equal to the number of protons. We know that the atomic number determines the identity of an element, thus an atom with a mass number of 197 and 118 neutrons must have 79 protons. Thus the element is gold .

The atomic number of aluminum is 13, which means it has 13 protons. All atoms with 13 protons are called aluminum. The mass number of aluminum is 27 and is the sum of neutrons and protons. We simply subtract the number of protons from the mass number to get the number of neutrons. Normally there are an equal number of electrons and protons. But since this aluminum exists as an ion with a +3 charge, it has lost three electrons and has only 10 electrons.

Chlorine-35 and chlorine-37 are isotopes of each other. Isotopes are atoms of the same element that have different masses due to different numbers of neutrons.