Science Vocabulary

Absolute zero temperature

the theoretical temperature at which the volume of an ideal gas is zero and all molecular motion stops

Absorption spectrum

the spectrum produced when atoms absorb specific wavelengths of incoming light and become excited from lower to higher energy levels; this pattern of absorption can be used in identifying an element.

Acids

a class of compounds that produce an excess of hydrogen ions (H^+) when in water solutions; such solutions will test below 7 on the pH scale

Activation energy

in a collision of reactants, the amount of energy required for a reaction to form transition states and proceed to products

Activity series

an arrangement of metals sequenced in decreasing order of their ability to act as a reducing agent in aqueous solutions

Alchemy

a practice that was particularly popular during the Middle Ages that focused on trying to change other metals into gold or silver

Allotrope

one of several possible forms of an element; for instance, carbon can be graphite, diamond, or buckminsterfullerene (commonly called "buckyballs").

Alloy

a solid or liquid mixture of two or more metals; some common alloys include steel, brass, and bronze.

Alpha decay

a type of radioactive decay where the nucleus emits two neutrons and two protons, which is the equivalent of a helium nucleus, 4/2He^2+

Alpha particle

the helium nucleus, 4/2He^2+, emitted in an alpha decay

Amphoteric

describes a substance that can behave as either an acid or base

Anion

any negatively charged ion

Anode

the positive electrode of an electrolytic cell and the site of oxidation

Aqueous solution

a solution made by dissolving a substance in the solvent water

Arrhenius, Svante

Swedish Nobel Laureate chemist known for his theory on acids and bases

Atom

the smallest whole unit of an element that contains a nucleus and electrons around the nucleus and is neutrally charged

Atomic mass

the average mass of an atom of an element; it is the weighted average of the isotopes based on the proportion of each isotope in a given element sample.

Atomic mass unit

Abbreviated amu and also called a Dalton, it is the mass equal to 1/12 the mass of a carbon-12 atom.

Atomic number

the number of protons in the nucleus of an atom; this identifies the type of atom; for example, all atoms with seven protons are nitrogen.

Atomic radius

half the distance between two adjacent atoms in an element's crystal

Avogadro's law

a gas law that states that equal volumes of an ideal gas contain equal numbers of particles at constant temperature and pressure and thus the volume of a gas is directly proportional to the number of moles of the gas

Avogadro's number

a number representing the number of atoms in 12.0 g of C-12; the number is 6.022 x 10^23

Base

any substance that produces an excess of OH^- ions in aqueous solution

Beta decay

radioactive atom decay that emits a charged particle; if this particle is negative, then it is an electron; if it is positive, then it is called a positron.

Beta particle

a negatively charged or positively charged particle with the mass of an electron that is emitted in beta decay

Binary

describes a substance made of two elements

Body-centered cubic

a unit cell of a crystal where there is a particle at each corner of a cube and one in the center

Bohr model of the atom

a model of the atom where electrons orbit the nucleus like planets around the sun, but at predetermined distances; electrons can transition from one orbit to a different empty one.

Boiling point

the temperature at which the vapor pressure of a liquid substance equals the atmospheric pressure; normal boiling points are defined at 1 atmosphere of pressure.

Boltzmann constant

defines the relation between absolute temperature and the kinetic energy contained in each molecule of an ideal gas; it is equal to 1.380649×10^−23 J∙K^−1.

Boyle's law

a gas law stating that the volume of a gas is inversely proportional to its pressure when the number of gas molecules and the temperature remain constant; P1 V1 \= P2 V2

Brass

an alloy of primarily copper and zinc with varying proportions of each metal

Brønsted-Lowry acid-base theory

an acid-base theory based on the transfer of a proton; according to this theory, an acid is a proton donor, and a base
is a proton acceptor.

Buret

a liquid measuring device used in titrations; the liquid is dispensed through the bottom of the device via a stopcock that opens and closes to control the flow of liquid.

Calorimetry

the measurement of heat evolution or absorption in chemical reactions

Calx

the powdery substance that remains after a metal or mineral is burnt; now known as an oxide

Catalyst

a substance that increases the rate of a chemical reaction by lowering the activation energy needed for the reaction by altering the reaction pathway

Cathode

the negative electrode of an electrolytic cell and the site of reduction

Cation

any positively charged ion

Cell potential

electromotive force (emf) or cell voltage; the electrical potential difference between the two electrodes in an electrolytic cell

Charles's law

a gas law that states that at constant pressure, the volume of a fixed amount of gas is proportional to its absolute temperature

Chemical bond

an attractive force that exists between two atoms such that the combination of atoms behaves as a unit that requires force (energy) to break apart

Chemical formula

a written expression using symbols and subscripts to indicate the number and type of each atom in a chemical unit

Chrome plating

the technique of electroplating a thin layer of chrome onto an object

Close-packed hexagonal

a crystal structure based on a hexagonal unit cell layering

Colligative properties

physical properties of solutions that depend on the ratio of the amount of solute to the solvent

Collision model

a model used to explain reaction rates using the number of molecules colliding per second with a certain required minimum energy

Combustion

a reaction involving oxygen as a reactant

Compound

a molecule that contains at least two different elements that are chemically combined in a fixed ratio

Concentration

the measurement of how much solute is in a given amount of solution; depending on the type of problem, different types of concentration units can be used, such as molarity and molality.

Covalent bond

the sharing of a pair of electrons by two atoms in a chemical bond

Covalent network

an extended lattice formed of covalent bonds, such as in SiO2
or diamond

Critical point

the endpoint of the liquid-gas curve on a phase diagram; it is the point at which a vapor and liquid become indistinguishable.

Crystalline

a solid with a well-defined lattice shape due to an orderly arrangement of its particles within the solid

Decomposition

a type of chemical reaction where a substance breaks down into simpler substances; such reactions have one reactant and two or more products.

Diffusion

the movement of one fluid through another from an area of high concentration to an area of lower concentration

Dipole

a polar molecule in which the centers of positive and negative charge are separated

Dipole moment

the product of one of the equal but opposite charges on two atoms in a molecule and the distance separating them

Diprotic

describes an acid capable of donating two
H^+ ions per molecule; for example, sulfuric acid, H2 SO4

Dispersion force

the intermolecular attraction between any two particles resulting from the polarization of the electrons in the electron clouds; also called London dispersion forces

Double replacement

the reaction of two ionic compounds to form two new ionic compounds

Ductile

the property of a metal that describes how easily the metal can be pulled into a wire without breaking

Effusion

the process by which a gas escapes from its container through a tiny hole

Electrochemical reduction

the transformation of metallic cations to metals by electron transfer; when a substance gains an electron, its oxidation state decreases, and thus it is reduced.

Electrochemistry

the division of chemistry that studies the relationship between reactions and electrical parameters such as voltage and current

Electrolysis

the nonspontaneous splitting of a substance by adding electrical energy; an example is the splitting of water into hydrogen and oxygen by applying a voltage and current.

Electron

a fundamental particle of matter that has a negative charge; discovered by J. J. Thompson in 1896

Electron affinity

the energy change, in kJ, when one mole of atoms of an element adds a mole of electrons (one per atom)

Electron "cloud"

the representation of the areas occupied by electrons in the atom; the types of electron clouds include ones with different shapes called "orbitals."

Electronegativity

the ability of an atom to attract shared electrons in relative units

Electroplating

the deposition of a thin coat of a metal onto the surface of an object by passing an electrical current through a salt solution containing the metal ion to be deposited

Electrostatic force

a force created by the attraction of oppositely charged ions or charged particles

Elements

the simplest type of substance with unique physical and chemical properties

Emission spectrum

the line spectrum produced when excited atoms return to lower energy levels and emit photons characteristic of the element; the pattern of emission can be used in identifying an element.

Empirical formula

a chemical formula reduced to lowest terms; for example, C2 H2 reduced to CH

Empiricism

the process of relying on experiments and observations in the natural sciences

Endothermic

describes a chemical reaction that absorbs heat from the surroundings

Endpoint

the point in an acid-base titration when the pH indicator changes color

Enthalpy

a thermodynamic quantity (H) that measures the heat content under constant pressure

Entropy

a thermodynamic quantity (S) that is a measure of the state of order in a substance

Equilibrium

the condition of a chemical reaction when the forward rate and the reverse rate are equal, so there is no apparent change

Equilibrium constant

the number obtained if concentrations and/or pressures of the products are divided by those of the reactants when the reaction is at equilibrium.

Equivalence point

the point in a titration when the moles of the two reactants are equal; in an acid-base titration, the moles of H^+ transferred equals the moles of OH^-

Exothermic

describes a reaction that releases heat to the surroundings

Face-centered cubic

describes a crystal structure that has atoms at each corner of the cube and six atoms at each face of the cube

Force

mass x acceleration or time derivative of momentum; force creates change in a physical system.

Galvanic electrochemical cell

a spontaneous reaction used to generate electrical potential (voltage) and deliver energy

Gas

a state of matter characterized by molecules being spread out from each other and therefore highly compressible; takes the shape of any container it is in, creating uniform pressure in all directions

Gibbs Free Energy

a thermodynamic quantity that indicates whether a reaction will be spontaneous and how much work it can do; a spontaneous reaction has a release of free energy (∆G) found from the equation ∆G \= ∆H-T∆S, where ∆H is the enthalpy change, and ∆S is the entropy change.

Group

a column on the periodic table; for example, alkali metals (group 1) or noble gases (group 18)

Heat

an amount of energy transferred from a hot system to a cooler system resulting in changes in molecular motion; measured in kilojoules

Heat of formation

the enthalpy change that occurs when a unit of mass of a compound is produced from its elements

Heat of fusion

the enthalpy change that occurs when a unit of mass of a solid substance melts

Heat of vaporization

the enthalpy change that occurs when 1 gram of a liquid substance vaporizes

Homogenous

describes a solution that features a uniform dispersion of its components

Hybridization

the process when electron orbitals like s and p mix together to form new orbitals such as sp; the total number of orbitals is conserved, so 1s + 1p electron orbitals yields 2sp hybrids.

Hydration

the process of being surrounded by water solvent molecules; this process can also form solid crystals called hydrates.

Hydrogen bond

a type of dipole-dipole force between molecules involving the attraction of a hydrogen, which is bound to one strongly electronegative atom, either a nitrogen, oxygen, or fluorine atom in another molecule; for example, the bond that occurs when the hydrogen in a water molecule is attracted to the nitrogen atom in an ammonia molecule.

Hydronium ion

a hydrogen ion (H^+) bonded to a water molecule in hydration to form H3O^+

Ideal gas equation

an equation that relates temperature, pressure, volume, and moles of gas together (PV\=nRT)