Kaplan MCAT General Chemistry Review

The effective nuclear charge is calculated by the following equation: Z_eff = Z - S, where Z is the atomic number (the number of protons in the nucleus), and S is the average number of electrons between the nucleus and the valence electrons (which is the equivalent of saying S is the number of inner or non-valence electrons). Because fluorine’s atomic number is 9, there are also 9 electrons in fluorine (not an ion). Of these 9 electrons, 7 are in the outer shell (valence) and 2 electrons are inner electrons, therefore these electrons would have a Z_eff of the following: Z_eff = 9 - 2 = 7. Now for the fluoride ion, there are now 10 total electrons. However, there are still only 2 inner electrons, so these 8 outer electrons would have a Z_eff of the following: Z_eff = 9 - 2 = 7. Without changing the number of inner electrons, the effective nuclear charge will not change. This would affect the radius, however, as fluoride now has 8 valence electrons distributing the same Z_eff of 7, whereas fluorine has only 7 electrons sharing the Z_eff of 7. This is why anions are larger than their respective unionized species.

52. B

(B) is correct because the highest electron shells, or orbitals, are most loosely held by the nucleons and thus are most available for bonding. 3s is higher than any other level (A), but it is unoccupied in the fluoride ion. (C) and (D) are lower energy levels/orbitals than 2p.

1

Information for this entire passage taken primarily from: www.thepigsite.com/articles/4/waste-and-odor/914/manure-to-energy-the-utah-project(C₆H₁₃O₅ + xH₂O → COOH–(CH₂) _n–CH₃ → 4CH₄ + 2CO₂) With contributions from: extension.missouri.edu/xplor/agguides/agengin/g01881.htm (H₂ + CO₂ → H₂O + CH₄) books.google.com/books?id=ndPuyf4BsXYC&pg=PA26&lpg=PA26&dq=methane+and+bacteria+equation&source=web&ots=sbBVmswSMF&sig=6pQeW_uEd6WiSvcgPuHf_YdYQ4M&hl=en&sa=X&oi=book_result&resnum=5&ct=result CH₃COOH → CH₄ + CO₂ CO₂ + 4H₂ → CH₄ + 2H₂O

Glossary

Absolute zero The temperature at which all substances have no thermal energy; 0K or -273.15°C.

Absorption spectrum The series of discrete lines at characteristic frequencies representing the energy required to make an electron in an atom jump from the ground state to an excited state.

Acid A species that donates hydrogen ions and/or accepts electrons. See acidic solution; arrhenius acid; brønsted-lowry acid; lewis acid.

Acid dissociation constant (K_a) The equilibrium constant that measures the degree of dissociation for an acid under specific conditions. For an acid HA,

Acidic solution An aqueous solution that contains more H⁺ ions than OH^- ions. The pH of an acidic solution is less than 7.

Activated complex The transition state of a reaction in which old bonds are partially broken and new bonds are partially formed. The activated complex has a higher energy than the reactants or products of the reaction.

Activation energy (E_a) The minimum amount of energy required for a reaction to occur.

Adiabatic process A process that occurs without the transfer of heat to or from the system.

Alkali metals Elements found in Group IA of the periodic table. They are highly reactive, readily losing one valence electron to form ionic compounds with nonmetals.

Alkaline earth metals Elements found in Group IIA of the periodic table. Their chemistry is similar to that of the alkali metals, except that they have two valence electrons and, thus, form 2⁺ cations.

Amphiprotic species A reaction species that may either gain or lose a proton.

Amphoteric species A species capable of reacting as either an acid or base, depending on the nature of the reactants.

Anion An ionic species with a negative charge.

Anode The electrode at which oxidation occurs. Compare cathode.

Antibonding orbitalMolecular orbital formed by the overlap of two or more atomic orbitals whose energy is greater than the energy of the original atomic orbitals. Compare bonding orbital.

Aqueous solution A solution in which water is the solvent.

Arrhenius acid A species that donates protons (H⁺) in aqueous solution (e.g., HCl).

Arrhenius base A species that gives off hydroxide ions (OH^-) in aqueous solution (e.g., NaOH).

Atom The most elementary form of an element; it cannot be further broken down by chemical means.

Atomic mass The averaged mass of the atoms of an element, taking into account the relative abundance of the various isotopes in a naturally occurring substance. Also called the atomic weight.

Atomic mass units (amu) A unit of mass defined as the mass of a carbon-12 atom; approximately equal to the mass of one proton or one neutron.