chemistry regents

Acid

An electrolyte that produces H+ (H3O+) as the only positive ion in solution and has a low pH.

Activation Energy

The minimum amount of energy that is needed to initiate a reaction by producing an activated complex.

Activated Complex

The temporary, unstable molecule that forms when reactants receive sufficient activation energy.

Alloy

A homogeneous mixture (solution) of 2 or more metals.

Solution

A homogeneous mixture.

Alpha Decay

A transmutation in which a helium nucleus (alpha particle) is released by the nucleus of an unstable atom resulting in a decrease in atomic number by 2amu and mass number by 4amu.

Anion

A negatively charged ion.

Cation

A positively charged ion.

Aqueous

A solution in which water is the solvent. For example, NaCl(aq).

Atomic Mass

The weighted average mass of all naturally occurring isotopes of an element based on percent abundance.

Atomic Mass Unit (amu)

A relative mass scale based on 1/12 the mass of a Carbon 12 atom.

Atomic Number

The number of protons in the nucleus of an atom. Used for identification of elements and organization of the Periodic Table of Elements.

Atom

The smallest particle of an element that has all of the properties of that element. It is electrically neutral because the number of protons equals the number of electrons in atoms.

Avogadro's Hypothesis

Equal volumes of gases under the same conditions of temperature and pressure have the same number of molecules regardless of their identities.

Base

An electrolyte that yields hydroxide ions (OH-) as the only negative ions in solution and has a high pH. May also be described as accepting H+ from solution.

Beta Particles

High velocity streams of electrons emitted from the nucleus of unstable atoms during a transmutation and causing an increase in atomic number by 1amu.

Boiling Point

The temperature at which the vapor pressure of a liquid is equal to the pressure exerted on the liquid. The normal boiling point is measured at standard pressure (1 atm or 101.3 kPa).

Calorimeter

An apparatus for measuring the quantity of heat released or absorbed during a reaction.

Catalysis

A change in the rate of a reaction by the presence of a substance that is unchanged at the end of the reaction.

Catalyst

A substance that increases the rate of a reaction by lowering the activation energy needed to form an activated complex. It affects both the forward and reverse reaction and is not altered during the reaction.

Cathode Rays

Streams of negatively charged particles (e-) that emanate from the cathode of a discharge tube. Led to the discovery of electrons in atoms.

Celsius Scale

Temperature scale based on the freezing and boiling points of water. Uses the same size units as the absolute (Kelvin) scale, which is based on absolute zero.

Absolute Temperature Scale

Temperature scale based on absolute zero. Measured in Kelvin's which have the same size units as degrees Celsius.

Intramolecular Chemical Bond

Associations that form between atoms that are attracted to the same electrons. May be ionic (transfer of electrons from metal to nonmetal followed by attraction of oppositely charged ions), covalent (sharing of electron pairs between 2 nonmetal atoms), or metallic (cations immersed in a sea of mobile (delocalized) electrons). Intramolecular Bonds form molecules/formula units).

Intermolecular Forces of Attraction

Associations that form between molecules. Examples include dipole-dipole (attraction between partial charges on neighboring polar molecules), molecule-ion (attractions between polar molecules and neighboring ions of opposite charge), London Dispersion (van derWaal's or weak) Forces (attractions between molecules based on temporary dipoles formed due to electron movement), and Hydrogen Bonds (H with F, O, or N in 2 or more molecules).

Chemical Change

A change in the composition of substances with accompanying changes in properties due to a chemical reaction.

Chemical Equilibrium

The dynamic condition in which a reversible reaction has reached a state of equal rates of the forward and reverse reactions and constant concentrations of reactants and products (RECC).

Chemical Property

The ability of a substance to react or not react with another substance.

Coefficients

The numbers preceding the formulas in a balanced chemical equation that are used to indicate the smallest mole ratios of reactants and products in a chemical reaction.

Collision Theory

Assumption that particles must collide with sufficient energy and at the correct angle in order for a chemical reaction to occur.

Combustion

A chemical reaction that combines a reactant with oxygen and releases light and heat energy among other products.

Compound

A substance of definite composition that may be decomposed into 2 or more elements by chemical change.

Concentration

The quantity of a substance in a given volume of solution, expressed as molarity, percent, or ppm.

Condensation

The physical process by which a a gas or vapor changes to a liquid by releasing heat energy.

Law of Conservation of Matter

The total mass, charge, and energy of the reactants must be equal to the total mass, charge, and energy of the products in a chemical or physical change.

Crystal

The solid form of a substance in which there is a definite shape due to the arrangement of molecules/atoms/ions in a definite, repeated pattern

Radioactive Decay

The spontaneous transmutation of an unstable nucleus into a more stable nucleus through the emission of energy and/or particles.

Decomposition

A chemical change in which a single substance breaks down to form 2 or more simpler substances. aka analysis.

Deposition

The change in state of a substance in the gaseous stand directly to a solid without a liquid phase.

Sublimation

The change in state of a substance in the solid state directly to the gaseous state without a liquid phase. Substances that sublime have weak intermolecular forces of attraction.

Density

The amount of mass per unit of volume. Units are g/cm3 or g/ml. Water has a density of 1g/ml.

Diatomic

Molecules that consist of 2 atoms. In nature, there are 7 elements that exist as diatomic molecules when they are not combined in compounds. HOFBrINCl

Monatomic

Molecules that exist as single atoms that are stable alone. These are the Noble Gases which are stable due to their full valence electron shells.

Dipole

A polar molecule, which is a molecular compound with asymmetrical charge distribution. Has partial positive and negative charges. Examples: HCl, H2O, NH3, CH3Cl etc.

Dissociation

Separation of ions in an ionic compound (electrolyte) when it is either melted (fused) or dissolved in water (aqueous). Dissociated ions are able to conduct electricity due to their movement. "Moving Charged Particles."

Distillation

The separation of a mixture of substances due to their differences in boiling points.

Double Bond

A covalent bond between 2 nonmetals in which 2 pairs of electrons (4 total electrons) are shared.

Double Replacement Reaction

A type of chemical reaction in which 2 ionic compounds exchange their anions and form 2 different ionic compounds. One of the products must be molecular (water), a gas (H2S), or a precipitate (insoluble on Table F).

Ductility

The physical property of metals that allows them to be drawn into wires.

Electrical Conductivity

Ability to allow electrical charge, such as ions in solution or electron in wires, to move from one place to another.

Electrolyte

A substance (acid, base, or salt) whose water solution conducts electric current.

Electron

A subatomic particle with a mass of 0amu and charge of -1. It is found in the orbitals/energy levels/electron cloud of an atom.

Electronegativity

A measure of the attraction of a nucleus for the electrons in a bond. The higher the electronegativity value the greater the attraction for an electron. Found on Table S.

Electron Configuration

A notation that indicates how many electrons are in each energy level around an atom. The electron configuration shown of the Periodic Table is for atoms in the ground state, which is the lowest energy and most stable arrangement.

Lewis Electron Dot Diagrams

Representations of atoms or ions showing the symbol of the element surrounded by the valence electrons shown in pairs. Ions either show a positive charge and empty outer shell due to loss of valence electrons or a negative charge, full outer shell, and brackets due to gain of electrons.

Element

A substance that cannot be decomposed by chemical or physical means.

Empirical Formula

A formula showing the simplest ratio of elements in a compound.

Endothermic Reaction

A reaction in which the products have greater potential energy than the reactants. Enthalpy (^H) is positive.

Energy

The ability to do work or cause change. It may be transferred and transformed but may not be gained or lost.

Enthalpy

Heat of Reaction (^H). A measure of the difference of potential energy between reactants and products. Endothermic reactions have a positive value and exothermic reactions have a negative value, making them spontaneous.

Entropy

A measure of the randomness or disorder of particles. Systems in nature favor higher entropy.

"Lazy and Crazy"

Systems in nature tend to move toward low energy and high entropy.

"BARF"

BREAK bonds ABSORB energy; RELEASE energy when bonds FORM.

"RECC"

At equilibrium, RATES are EQUAL and CONCENTRATIONS are CONSTANT.

Evaporation

The physical change in which a substance in the liquid state changes to the gaseous state by absorbing heat energy.

Exothermic Reaction

A reaction in which the reactants have greater potential energy than the products.

Families/Groups

Vertical columns on the Periodic Table in which the members have similar chemical properties due to having the same number of valence electrons.

Periods

Horizontal rows of the Periodic Table in which there is a repetition of properties from metal to transition metal to metalloid (semimetal) to nonmetal to noble gas at each level.

Excited Atom

The state of an atom when it has gained energy and an electron has moved to a higher energy level. This electron will release light energy as it returns to ground state. The release of energy will create a unique set of spectral lines that can be used to identify the element.

Filtration

A method using a porous barrier to separate insoluble solids from a mixture.

Nuclear Fission

A nuclear reaction in which large unstable nucleus (such as Uranium) is bombarded with neutrons that split it into smaller nuclei releasing a large amount of energy.

Nuclear Fusion

A nuclear reaction in which light nuclei (such as hydrogen) combine to form a heavier nucleus (such as helium), releasing a large amount of energy.

Formula Mass (Gram Formula Mass or Molecular Mass)

The sum of all of the atomic masses in the formula of a compound (the mass of each element is multiplied by its subscript and then added together).

Freezing Point

The temperature at which both the solid and liquid phases of a substance can exist in equilibrium.

Freezing Point Depression

The lowering of the normal freezing point of a liquid by the addition of solute. Ionic substances (salts) have a great impact that molecular substances due to dissociation into multiple particles.

Gamma Rays

Electromagnetic waves with the shortest wavelengths and highest frequencies; emitted by all nuclear reactions.

Gas Phase

The phase of matter with no definite shape or volume. It will assume the shape and volume of its container. Particles have constant,random, straight-line motion, little attraction to each other, elastic collisions, and virtually no size compared to the volume that they occupy.

Ground State

The condition of an atom in which electrons occupy the lowest available energy levels.

Half-life

The length of time needed for one-half of a given radioactive substance to undergo decay.

Halogen

A member of group 17 of the Periodic Table, the only group to have a 3 states of matter represented (F and Cl are gases, Br is liquid, and I is solid). All members have 7 valence electrons and tend to gain 1 from metals in groups 1 or 2 to form ionic compounds (halides...salts).

Heat

The most random form of energy. Moves from hot to cold.

Heat of Fusion

The amount of heat needed to change 1g of a substance from solid to liquid or the amount of heat released when 1g of a liquid changes to solid. For water, the value is 334J/g.

Heat of Vaporization

The amount of heat needed to change 1g of a substance from liquid to gas or the amount of heat released when 1g of a gas changes to liquid. For water, the value is 2260J/g.

Heterogeneous Mixture

A non-uniform mixture that has large particle size and uneven particle distribution.

Homogeneous Mixture

Solution; a uniform mixture with small particle size and even particle distribution.

Hydrogen Bond

An attraction that occurs between molecules that both have Hydrogen with one of the following elements that have a small radius and high electronegativity: Fluorine, Oxygen, or Nitrogen. This creates strong intermolecular attractions (due large to partial charges) that require large amounts of energy to separate. Responsible for the high boiling point of water and lower density of ice than liquid water.

Ideal Gas

Small gases with no attractions, negligible volume, perfectly elastic collisions, and constant random, straight-line motion. These do not exist in nature but, Hydrogen and Helium are the closest. To make any gas act more like an ideal gas, raise the temperature and lower the pressure. Ideal gases exhibit all of the principles of the Kinetic Molecular Theory.

Insoluble

A substance that does not dissolve in water. These substances tend to form precipitates in water.

Ion

A charged atom or group of atoms that have gained or lost electrons and are now charged.

Polyatomic Ion

A group of covalently bonded atoms that have collectively gained or lost electrons so that there is an overall charge on the group. This group can form ionic bonds with oppositely charged atoms.

Ionization Energy

The amount of energy needed to remove an electron from the valence shell of a neutral atom. Highest for Noble Gases, then nonmetals. Lowest for metals.

Isotopes

Nuclei of a given element that have the same number of protons but, a different number of neutrons and therefore, a different mass number.

Joule

Unit of energy. It takes 4.18 J to raise the temperature of 1 g of water by 1 degree Celsius.

Kernel

The nucleus and nonvalence electrons of an atom. Represented as the symbol of an element in a Lewis Electron Dot diagram.

Kinetic Energy

Energy of Motion.

Liquid

A phase of matter having definite volume but, taking the shape of its container.

Litmus

An indicator that turns red in acid and blue in base.

Malleable

A physical property of metals in that they can be flattened into sheets by hammering. Not brittle.

Mass Defect

The difference between the mass of an atom and the sum of the masses of its individual components. Atoms usually weigh a little less than if you added up the weights of all the particles. This is because that extra mass was converted into the energy during nuclear reactions.

Mass Number

The sum of the protons and neutrons in the nucleus of an atom.