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MCAT G. CHEM
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Solution equilibrium


When a solute is dissolved in a solvent, it will dissociate until reaching an equilibrium point at which the rate of dissociation equals the rate of precipitation of the solute, regardless of any additional solute introduced into the mixture


solvation


sol, a chemical process in which solvent molecules and molecules or ions of the solute combine to form a compound


Solvent


substance in which a solute is dissolved to form a solution


Acid dissociation constant


An equilibrium expression used to measure weak-acid strength, given by the ratio of the product of the products' molar concentrations to the product of the reactants' molar concentrations, with each term raised to the power of its stoichiometric coefficient. Denoted Ka.


Amphoteric


having characteristics of both an acid and a base and capable of reacting as either


Common ion effect


The molar solubility of one salt is reduced when another salt, having a common ion is brought into the same solution


Molar solubility


The molar amount of a solute that can dissolve in 1L of solvent until equilibrium-saturation-is reached


Arrhenius Definition


defined acids as subtsances that produced H ions in water, while bases produced OH ions. When they reacted together, H and OH neutralise to make water


Bronsted-Lowry definition


Common definition of acids as proton (H+) donors and bases as proton acceptors


Buffer


an ionic compound that resists changes in its pH


Conjugate acids and Bases


Systematic pairing of a deprotonated species (base) with its protonated form (conjugate acid). Conjugates appear on opposite sides of a chemical equation.


Diprotic Base


A base that can accept two moles of H+ per mole of itself (ex: SO₄²-).


Equivalence point


The point during a titration when the number of H+ ions and OH- ions are equal. This is at the middle of the steepest part of the titration curve.


Azeotrope


mixture of 2 or more substances that distills at a constant temperature and with constant composition, even though seperately the components have different boiling points


Colligative properties


A physical property of a solution that depends on the number, but not the identity, of the disswolved solute particles; example properties include vapor pressure lowering, boiling point elevation, osmotic pressure, and frezzing point depression


Phase diagram


a graph of pressure versus temperature that shows the conditions under which the phases of a substance exist


Ion


an atom, radical, or molecule that has gained or lost one or more electrons and has a negative or positive charge


Ion product


Product of the molar concentrations of dissociated ions in solution at any point in the reaction other than equilibrium or saturation, where each ion is raised to the power of its stoichiometric coefficient. Denoted IP.


Molality


The ratio of the number of moles of solute dissolved in one kilogram of solvent. molality (M = moles solute/kg of solution)


Alkaline earths


Slightly less reactive than alkali metals, comprise group II


Graham's Law


temperature is constant; effusion and temperature are proportional to the square root of their masses


Effusion


The process by which a gas escapes from one container to another at lower pressure through a tiny hole in the container.


Raoult's Law


The vapor pressure of solution is the product of the mole fraction of the solvent and the vapor pressure of the pure solvent. P_a=X_aP_total


Nucleus


the center of the atom which contains the protons and neutrons; in cells, structure that contains the cell's genetic material (DNA) and controls the cell's activities


Net ionic equation


A representation of a displacement reaction showing only the reactive species and omitting the spectator ions.


Percent composition


The Percent by mass of each element in a compound.


Percent yield


the ratio of the actual yield to the theoretical yield for a chemical reaction expressed as a percentage; a measure of the efficiency of a reaction


single displacement reaction


a reaction in which atoms of one element take the place of atoms of another element in a compound


Theoretical yield


the amount of product that can be made in a chemical reaction based on the amount of limiting reactant


Titration


a measured amount of a solution of unknown concentration is added to a known volume of a second solution until the reaction between them is just complete


Water dissociation Constant


Expression of auto-ionization of water into H+ and OH-at a certain temperature, given by the product of the ions' molar concentrations. Denoted by Kw and equal to 10-¹⁴ at 25˚C. Kw = [H+][OH-]


Dispersion Forces


attractions between molecules caused by the electron motion on one molecule affecting the electron motion on the other through electrical forces; these are the weakest interactions between molecules


Formal Charge


Charge assigned to an atom in a molecule or polyatmic ion, calculated by (# valence electrons) - (# 1/2 bonding electrons) - (# nonbonding electrons). Molecules containing atoms with lower formal charges tend to be more stable than those with higher formal charges.


Hydrogen bonding


the intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule


Intermolecular forces


Attractive and repulsive forces between molecules that are weaker than forces within molecules.


Ionic Bond


a chemical bond in which one atom loses an electron to form a positive ion and the other atom gains to electron to form a negative ion


Half equivalence point


where half of the acid is neutralized by the base on a titration curveAn acid dissociation constant, Ka, (also known as acidity constant, or acid-ionization constant) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions. The equilibrium can be written symbolically as: HA A− + H+, where HA is a generic acid that dissociates by splitting into A−, known as the conjugate base of the acid, and the hydrogen ion or proton, H+, which, in the case of aqueous solutions, exists as a solvated hydronium ion.


Nonpolar covalent bond


A covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge


Octet Rule


atoms react by gaining or losing electrons so as to acquire the stable electron structure of a noble gas, usually eight valence electrons


Atomic weight


The weight in grams of one mole of a given elementand is expressedin tems of grams per mole.


Avagadros number


the number of atoms in exactly 12 g of pure 12c and equal to 6.022 x 10^23 is called


atomic theory


(chemistry) any theory in which all matter is composed of tiny discrete finite indivisible indestructible particles


quanta


Small discrete increments of energy.


quantum


(physics) the smallest discrete quantity of some physical property that a system can possess (according to quantum theory) E=hf


Planck's Constant


A fundamental constant, h, that relates the energy of light quanta to their frequency: h = 6.6 X 10^-34 joule·second


The bohr model


1913, Niels Bohr, said that electrons formed specific layers instead or random ones, said atoms atoms absorb and give off energy when the electrons move from one shell to another


angular momentum in the bohr model


nh/2π The angular momentum changes only in discete amounts with respect to the quantum number. Also E=-R_h


Rydberg constant


2.18 x 10^-18 J/electron


Ground state


the lowest allowable energy state of an atom


electromagnetic energy of photons emmited from electrons at ground state


E=hc/λ


atomic emission spectrum


a set of frequencies of electromagnetic waves given off by atoms of an element; consists of a series of fine lines of individual colors


Balmer series


A set of spectral lines that appear in the visible light region when a hydrogen atom undergoes a transition from energy levels n>2 to n=2.


Lyman series


Set of spectral lines appearing in the UV region when a hydrogen atom undergoes a transition from energy levels n>1 to n=1.


Atomic absorption Spectra


Spectrum of certain absorbed wavelengths of light corresponding to an atom's spectrum of emitted frequencies of light. Unique to each element. AAS can be used to indentify an element.


heisenberg uncertainty principle


states that it is impossible to determine simultaneously both the position and momentum of an electron or any other particle


quantum numbers


numbers that specify the properties of atomic orbitals and of their electrons


Pauli exclusion principle


no two electrons or protons or neutrons in a given system can be in states characterized by the same set of quantum numbers


energy state


a definite stable energy that a physical system can have


Principle quantum number


The quantum number that indicates the main energy level occupied by the electron. Can theoretically take on any positive interger. Denoted by the letter n.


azimuthal quantum number


Second quantum number, designated by the letter "l." This "angular momentum" refers to the subshells within each principle quantum energy level. It can take on the value of an integer in the 0 to (n-1) range. The four subshellscorresponding to l=0,1,2,3 and are known as s,p,d,and f subshells.


Magnetic quantum number


specifies the specific orbital in which the electron is most likely to be found., Third quantum number, designated as ml. Describes a particular orbital within a subshell where an electron is very likely to be found. Possible values are integers in the -1 to 1 range, including 0.


Spin quantum number


The quantum number that has only two possible values, +1/2 and -1/2, which indicate the two fundamental spin states of an electron in an orbital


electron configuration


the ways in which electrons are arranged in various orbitals around the nuclei of atoms


hund's rule


orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin


representative elements


an element in an "A" group in the periodic table; as a group these elements display a wide range of physical and chemical properties. In their atoms, the s and p sublevels in the highest occupied energy level are partially filled


lathanide series


rare earth element group (elements 58-71)


actinide series


(chemistry) a series from actinium to lawrencium of 15 radioactive elements with increasing atomic numbers


transition elements


Elements in the middle of the periodic table, in groups 3-12.


atomic radius


one-half the distance between the nuclei of two atoms of the same element when the atoms are joined


indicator


(chemistry) a substance that changes color to indicate the presence of some ion or substance


Lewis definition


Acids defined as electron-pair acceptors and bases as electron-pair donors.


Neutralization reaction


the reaction of the ions that characterize acids and the ions that characterize bases to form water molecules and a salt


Normality


Gram equivalent weight of solute per liter of solution, often denoted by N.


pH


(chemistry) p(otential of) H(ydrogen)


pI


pH of a molecule at which it contains no net electric charge, isoelectric point.


Strong acid


An acid that will completely dissociate in aqueous solution, like HCl, HI, HClO₄ HBr.


Triple point


the point on a phase diagram that represents the only set of conditions at which all three phases exist in equilibrium with one another


Molarity


a concentration unit of a solution expressed as moles of solute dissolved per liter of solution


Henderson Hasselbalch Equation


pH=pka+log[base/acid] Used in titration based problems that relates the pH or pOH of a solution to the pK and the ratio of the dissociated species.


Neutron


an elementary particle with 0 charge and mass about equal to a proton


Resonance structure


structure that occurs when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion


VSEPR


Valence Shell Electron Pair Repulsion theory, stating that the three-dimensional molecular geometry about some central atom is determined by the elctronic repulsion between its bonding and nonbonding electron pairs.


Combination Reaction


a reaction in which two or more substances combine to form a single substance A+B>>>>>>>C


Decomposition reaction


(chemistry) separation of a substance into two or more substances that may differ from each other and from the original substance C>>>>A+B


Disproportionation


Redox reaction, in which the same species is both oxidized and reduced.


Covalent Bond


a chemical bond that involves sharing a pair of electrons between atoms in a molecule


Effective nuclear charge


Resulting positive nuclear charge an outer electron senses after accounting for the shielding effect of inner core electrons. Abbreviated as Z(eff). Increases from left to right, and bottom to top on the Periodic Table.


Charles and Gay Lussac's Law


At a constant pressure, the volume of an ideal gas is directly proportinal to its temperature: V (a) T


Diffusion


process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated


electron affinity


Energy released when an atom or ion in the gaseous state gains an electron. Increases from left to right and from bottom to top on the Periodic Table.


Electronegativity


the tendency for an atom to attract electrons to itself when it is chemically combined with another element


Free radical


an uncharged molecule with a single unpaitred electron in its outer ring, very unstable, exists for only about 10 seconds


Halogens


Contains nonmetals, 7 valence electrons in it's outermost energy level. Very reactive


Ionization energy


the energy required to remove an electron from a gaseous atom; generally increases in moving from left-to-right across a period and decreases in moving down a group


Mass number


Sum of the protons and neutrons in an element often denoted by the letter A


Emperical Formula


simplest whole # ration of atoms in a compound


Concentration


tells you how much solute is present compared to the amount of solvent


Electrolyte


a substance that, when dissolved in water, results in a solution that can conduct electricity


Redox Half Reaction


The hypothetical equation showing only the species that is oxidized or reduced in a redox reaction and the correct number of electrons transferred between the species in the complete, balanced equation.


Lewis structure


a structural formula in which electrons are represented by dots; dot pairs or dashes between two atomic symbols represent pairs in covalent bonds.


Molecular orbital


Region in a molecule where atomic orbitals overlap, resulting in either a stable low-energy bonding orbital or an unstable high-energy antibonding orbital.


Formula weight


Sum of all the masses, in AMU, present in one molecule of a molecular compound.


STP


Standard Temperature and Pressure. 273 Kelvin (0 Celsius), 1 atmosphere (760 torr, 760 kPA).


Vapor pressure


the pressure exerted by a vapor in equilibrium with its liquid or solid phase


Aqueous Solution


a solution in which water is the solvent


Henry's Law


the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid


Solubility Product Constant


Product of the molar concentrations of dissociated ions in solution at saturation, where each ion is raised to the power of its stoichiometric coefficient. Denoted Ksp.


Solute


in a solution, the substance that dissolves in the solvent


Proton


a subatomic particle that has a positive charge and that is found in the nucleus of an atom Charge of +1 and mass of 1.0073 amu


Activation energy


The amount of energy that reactants must absorb before a chemical reaction will start; also called free energy of activation.


Chemical Kinetics


the area of chemistry that is concerned with reaction rates and reaction mechanisms


Collision theory of chemical Kinetics


Theory stating that the rate of a reaction is directly proportional to the number of collisions that take place between reactants per second.


Equilibrium


a dynamic condition in which two opposing changes occur at equal rates in a closed system


Equlibrium constant


Keq describes the ratio of product concentration to reactant concentration, with each raised to the power corresponding ot its coefficient ion in the balanced equation


Le chateliers Principle


States that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress.


Rate determining step


the slowest elementary step which is the limit for the rate of the other steps


Rate law


An emperimentally determined mathmatical expression showing the rate of a reaction as a function of the concentration of its reactants


Reaction mechanism


Play-by-play showing the individual steps of a reaction, including the formation and destruction of any reaction intermediates that may occur.


Reaction order


The sum of the exponents in a rate law, where each exponent provides the reaction order with respect to its reactants


Dipole


a pair of equal and opposite electric charges or magnetic poles separated by a small distance


Dipole Dipole interaction


When polar molecules orient themselves such that the positive region of one molecule is close to the negative region of another molecule.


Ion dipole interactions


When dipoles are dissolved in a solution where ions are present ions wil arrange themselves with the opposite charged end of the dipole.


hydrogen bonding


the intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule


London forces


the weak attractive forces between molecules resulting from the small, instantaneous dipoles that occur because of the varying positions of the electrons during their motion about nuclei


compound


(chemistry) a substance formed by chemical union of two or more elements or ingredients in definite proportion by weight


molecule


two or more atoms held together by covalent bonds


molecular weight


(chemistry) the sum of the relative atomic masses of the constituent atoms of a molecule


empirical formula


a chemical formula showing the ratio of elements in a compound rather than the total number of atoms


mole


the amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12


gram equivalent weight


the weight in grams of compound that can be substituted by 1 atom of Hydrogen. GEW = MW / # of acidic Hyrdogens


law of constant composition


Any sample of a given compound will contain the same elements in the identical mass ratio.


percent composition


the percent by mass of each element in a compound


electrolysis


The process of decomposing a chemical compound by the passage of an electric current.


decomposition reaction


(chemistry) separation of a substance into two or more substances that may differ from each other and from the original substance


single displacement reaction


a reaction in which atoms of one element take the place of atoms of another element in a compound


redox reaction


A chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.


Period


a horizontal row of elements in the periodic table


Group 1A


Alkali metals: highly reactive, therefore always compounds., 1 valence electron +1 ion, Hydrogen H⁺, Lithium Li⁺, Sodium Na⁺, Potassium K⁺, Rubidium Rb⁺, Cesium Cs⁺


Group 2A


Alkaline Earth Metals, 2 valence electrons +2 ions, Magnesium Mg²⁺, Calcium Ca²⁺, Stronium Sr²⁺, Barium Ba²⁺less reactive than alkali metals


Group 3A


have three valance electrons. In certain instances, some elements will loose three electrons , but they will also share electrons with another element to attain stability.


Group 4A


4 valence electrons +4, -4 ions., Carbon Group can form covalent bonds with nonmetals. Only carbon forms strong pi bonds


pi bonds


Side-to side parallel orbitals overlap to share electrons, the 2nd/3rd covalent bond between two atoms, cannot rotate and maintain the bond.


Group 5A


5 valence electrons -3 ions, Nitride N³⁻, Phosphide P³⁻ - gain 3 electrons to become a noble gas - s2p3 can form 3 covalent bonds all but Nitrogen can form 5 covalent bonds using d orbitals. Can further bond with a lewis base to form asixth bond.


lewis base


an atom, ion, or molecule that donates an electron pair to form a covalent bond.


Group 6A


chalcogens,, Oxide O²⁻, Sulfide S²⁻, Selenide Se²⁻ - chalcogens - gain 2 electrons to become a noble gas - s2p4 Oxygen is the second most electronegative element.


Group 7A


halogens; ns2np5,, 2nd most reactive group, The Halogens; very active because of need to fill; form -1 ions; 7 electrons in valence shell; tend to form salts with elements from groups 1A and 2A


Noble gases


Contains nonmetals that are non-reactive. Full outermost energy level except helium which has 2.


s orbital


have the shape of a sphere, with the center of the sphere at the nucleus; completely symmetrical along all axes; 1s orbital is spherically symmetric and has no nodes; 2s orbital is also spherical but contains a node and is higher in energy


sigma bond


a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei


d orbital


5 different orbitals shaped like clover leaves and max electrons is 10


Ion


an atom or group of atoms that has a positive or negative charge


effective nuclear charge


The nuclear charge experienced by the outermost electrons of an atom (actual charge minus the shielding caused by inner shells: Z-eff)


subshell


A subdivision of an energy level in an atom. They are divided into orbitals.


periodic trends


property of the elements that can be predicted from the arrangement of the periodic table


atomic radius


one-half of the distance between the center of identical atoms that are not bonded together. Since effective nuclear charge increases when moving from left to right each additional electron is pulled more strogly toward the nucleus.


bond energy


the energy required to break a chemical bond and form neutral isolated atoms


bond length


the average distance between the nuclei of two bonded atoms


ionic cmpound


named after their cation and anion


physical reaction


a reaction where a compound does NOT change its molecular structure.


chemical reaction


the process by which one or more substances change to produce one or more different substances


theoretical yield


the maximum amount of product that can be produced from a given amount of reactant


redox reaction


A chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.


Bronsted Lowry


A model of acids and bases which an acid is hydrogen ion donor and base is a hydrogen ion acceptor.


Lewis acid base reaction


the formation of one or more covalent bonds between an electron pair donor and an electron pair acceptor


crystalline solid


solids in which the particles are arranged in a repeating, 3-D pattern, has a specific melting point, classified as ionic network covalent, metallic or molecular.


Network covalent


large molecular structures, strong covalent bonding, share qualities of IONIC AND COVALENT


polymer


a naturally occurring or synthetic compound consisting of large molecules made up of a linked series of repeated simple monomers


amorphous solid


A solid made up of particles that are not arranged in a regular pattern.