Understand basic chemistry - AP Biology

.. ..

:F — B — F: Boron can have a violated octet (6 e-) and each F has 3 lone pairs

.. | .. for a total of 9 pairs of unpaired electrons

:F:

..

Electrons are notably smaller than nucleons (protons and neutrons), however, they have an equal amount of charge to protons. This is why an atom with the same amount of protons as electrons is considered electrically neutral.

The nucleus itself is positively charged, as the electrons are located relatively far away from the atomic center.

Electronegativity is defined as the tendency of an atom to attract an electron in a bond that it shares with another atom. Because oxygen wants to receive two elctrons, while both sodiums wish to lose one electron, oxygen has a higher electronegativity than sodium. Typically, electronegativity can be seen as increasing as you go to the top right of the periodic table. For example, fluorine has a higher electronegativity than nitrogen.

In , the nitrogen is bound covalently to the three oxygens, and the complex has an overall of .

Sodium has a charge of , and is ionically bound to the complex.

When put into water, the compound will dissociate into and .

HCl is an ionic compound, while the other answer choices have only covalent bonds.

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 .

The octet rule requires that each atom in the molecule has eight valence electrons, fully filling the s and p subshells. Atoms that have a full octet tend to be more stable and lower in energy.

In the compound , each fluorine has seven initial valence electrons and boron has three initial valence electrons. Upon forming the compound bonds, boron shares its three electrons with each fluorine through covalent bonds. This givens each fluorine a full octet, but leave boron with only three covalent bonds, resulting in only six valence electrons. Boron does not satisfy the octet rule in this compound.

Each atom in the other listed compounds forms bonds to generate a full octet. Sodium chloride achieves this through an ionic bond. Methanal and diatomic oxygen both use double bonds to help achieve octets.

Ethene is an organic molecule composed of two carbon atoms, joined by a double bond, and four hydrogen atoms.

Ethene, like all molecules, exhibits London dispersion forces. This molecule, however, has no net dipole moment, so it will not exhibit dipole-dipole attraction. Also, even though it contains hydrogens, it does not exhibit hydrogen bonding. To exhibit hydrogen bonding, the hydrogen atoms must be attached to more electronegative atoms, namely nitrogen, fluorine, or oxygen. Finally, ionic bonding is only present in ionic compounds, not organic compounds.

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.

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 identity of an element is determined by the number of protons. One cannot alter the number of protons without altering the identity of the element. By adding a proton, the atomic number increases by one and the element identity changes.

Number of neutrons can be altered to create isotopes. Number of electrons can be altered to create ions.

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).

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 .

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.

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 .

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.

Hydrogen bonding takes place when a hydrogen atom is attracted to a highly electronegative atom in another molecule. Hydrogen bonding takes place between hydrogen and either nitrogen, oxygen, or fluorine. Carbon has an electronegativity similar to hydrogen's, and will not hydrogen bond with hydrogens in other molecules.

Only molecules with -OH, -FH, or -NH groups can form hydrogen bonds.

Ionic bonds most commonly form between metals and non-metals. Non-metals have high electronegativities and metals have low electronegativities. In these type of bonds, electrons are transferred from the metal to the non-metal because of the large difference in electronegativities. The non-metal will try to gain an electron (high electronegativity) and the metal will try to donate an electron (low electronegativity). The result is a complete electron transfer, known as an ionic bond.

Hydrogen bonds are intermolecular forces between hydrogens and adjacent molecules. These adjacent molecules must contain either fluorine, oxygen, or nitrogen, the three most electronegative atoms. These electronegative atoms pull electrons away from the bonded hydrogen, giving it a small positive charge and giving themselves a slightly negative charge. When the positive hydrogen of one molecule come close to a negative charge on another, the opposite charges attract and pull the molecules close together to form a hydrogen bond. The hydrogen must be bonded to oxygen (-OH), fluorine (HF), or nitrogen (-NH) to have this charging effect.