Glossary
A B C D E F G H I L M N O P Q R S T V
- acid
- a chemical that has a sour taste when aqueous, changes the color of acid-base indicators, reacts with bases to form salts and water, and conducts electric current. Arrhenius acids are chemical compounds that increase the concentrations of positive hydrogen ions in aqueous solution. Brønsted-Lowry acids are molecules or ions that are proton donors. A Lewis acid is an atom, ion or molecule that accepts an electron pair to form a covalent bond.
- anion
- a negatively-charged ion
- aqueous
- in solution with water as the solvent
- atom
- the smallest particle of a chemical element that still exhibits the characteristics of that element. An atom constitutes protons and neutrons in its nucleus and levels of orbiting electrons.
- atomic mass (or weight)
- the mass of one atom of a particular element, expressed in atomic mass units
- atomic mass units
- units used to express the mass of an atom, relative to the mass of a standard C-12 atom. One atomic mass unit equals one-twelfth the mass of a C-12 atom, or about 1.661 × 10-24 grams.
- atomic name
- the name of a chemical element
- atomic number
- indicates the number of protons in an element
- atomic radius
- the distance from the center of the nucleus of an element to the outer edge of its electron cloud. This characteristic follows a trend on the periodic table.
- atomic symbol
- the standard group of letters that represent an element. Most elements have only one- or two-letter symbols. These symbols are generally abbreviations of the scientific or common name of the element.
- base
- a chemical that has a bitter taste when aqueous, changes the color of acid-base indicators, feels slippery in dilute aqueous solutions, reacts with acids to produce salts and water, and conducts electric current. An Arrhenius base is a chemical compound that increases the concentration of hydroxide ions (OH-) in aqueous solution. Brønsted-Lowry bases are molecules or ions that are proton acceptors. A Lewis base is an atom, ion or molecule that donates an electron pair to form a covalent bond.
- boiling point
- the temperature at which the equilibrium vapor pressure of a liquid equals the atmospheric pressure
- bond energy
- the amount of energy required to break a certain bond
- bonds
- forces that hold atoms together
- cation
- a positively-charged ion
- charge
- the electrical energy present in an atomic particle
- chemical element
- the simplest form of matter; cannot be broken down; comprise only one type of atom
- compound
- matter that can be broken down by chemical methods; the products have different properties than the original compound
- conductors
- a thing that transmits heat, electricity, light, sound or other form of energy; most references to conductors on this website refer to those that transmit electricity
- constituent
- any component that makes up a whole
- covalent bonds
- bonds that have an electronegativity difference of less than 1.7. Covalent bonds involve a sharing of electrons and generally join two nonmetals.
- crystal lattice
- a three-dimensional arrangement of particles made up of unit cells. Crystalline solids comprise particles in an orderly, geometric, repeating pattern that is the crystal structure, or lattice.
- delocalized
- a state in which a particle has no particular orbit or domain
- density
- a ratio of mass and volume
- diatomic molecule
- a molecule comprising two atoms
- diffusion
- spontaneous mixing of particles of two substances caused by random motion
- dipole-dipole attraction
- an intermolecular force found between neutral, polar molecules
- ductile
- the ability to be drawn into wire form
A B C D E F G H I L M N O P Q R S T V
- effusion
- pressurized passing of particles through a tiny opening
- electron
- a negatively charged particle found in atoms
- electron affinity
- the energy change that occurs when an atom gains an electron
- electronegativity
- the attraction of an atom in a compound for an electron
- electron shells
- another term for energy levels
- endothermic
- a characteristic meaning an intake of energy, especially heat
- energy
- the capacity or ability to do work. Energy can exist in many forms including heat, light and electricity.
- energy (electron) levels
- simply put, rings around the nucleus of an atom in which specific electrons are most probably located. Particular electrons orbit in their own ring, or shell, with exceptions when they are excited or used in bonds. Electrons always fill the lowest possible energy level to its maximum extent before beginning to orbit (fill) a higher (farther from the nucleus) energy level. The general rule is that two electrons may occupy the first energy level, and eight in several subsequent levels.
- equilibrium vapor pressure of a liquid
- the pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature
- exothermic
- a characteristic meaning a release of energy, especially heat
- formula unit
- the smallest unit of a crystal lattice that still exhibits that properties of the structure. Also known as a unit cell.
- freezing point
- temperature at which the solid and the liquid of an element, compound, or mixture are in equilibrium at one standard atmosphere, also known as the melting point
- gas
- one of the four states of matter. Gases expand to fill their container, having no definite shape or volume. Intermolecular forces are insignificant, allowing particles to glide easily past each other (gases are fluids). Gases have low density, are compressible, and diffuse and effuse easily.
- group
- columns on the periodic table that contain elements with similar chemical properties
- hydrogen bonds
- special instances of dipole-dipole intermolecular forces. These IMFs — they are not bonds! — are very strong. They occur between molecules that both contain an oxygen, fluorine, or nitrogen. One molecule must also contain a hydrogen. This hydrogen is strongly attracted to one of the mentioned electronegative elements on the other molecule.
- intermolecular forces
- forces of attraction between molecules. IMFs are generally weaker than bonds.
- ion
- an atom or covalently-bonded molecule with an overall charge. Ions form ionic bonds with other ions
- ionic bonds
- bonds that have an electronegativity difference of greater than or equal to 1.7. Ionic bonds involve a strong attraction between two charged atoms or groups of atoms, resulting in a transfer of electrons, and usually involve a metal and a nonmetal when diatomic.
- ionic radius
- the distance from the center of the nucleus of a charged atom to the outer edge of its electron cloud. This characteristic follows a trend on the periodic table. Cations have smaller radii than their parent ions while anions have larger radii.
- ionization energy
- energy required to remove an electron from an atom (creating a cation)
- isotope
- any atom of an element, differentiated from a common form of the element by having a different number of neutrons in the nucleus. An atomic mass as noted on the periodic table (for most elements) is a weighted average of all the naturally occuring isotopes of that element, explaining why elements generally do not have a round mass figure.
- liquid
- one of the four states of matter. Liquids have a definite volume, but take the shape of their container. The particles glide easily past each other (liquids are fluids). Liquids, compared to gases, have a relatively high density and are incompressible. Surface tension and evaporation are characteristics of liquids.
- london dispersion forces
- very weak intermolecular forces found between nonpolar molecules. The slight attraction is created by the motion of the electrons around the atom. The orbits create instantaneous dipoles, or induced dipoles, to pull the molecules together. The greater the mass of two molecules, the greater the London dispersion force between them.
- malleable
- the ability to be hammered into sheets
- mass
- a quantity of matter, often referred to as weight
- melting point
- temperature at which the solid and the liquid of an element, compound, or mixture are in equilibrium at one standard atmosphere, also known as the freezing point
- metal
- an element as specified on the periodic table to be so. Metals conduct heat and electricity, are malleable and ductile, and have high tensile strength.
- metal activity
- a trait to demonstrate how chemically active an element is. This characteristic follows a trend on the periodic table.
A B C D E F G H I L M N O P Q R S T V
- metallic bonds
- bonds that involve a delocalization of valence electrons and join two metals. Outer shell electrons of each bonded atom are no longer attached to any one atom and instead form a sea of electrons. The strength of the bond increases when the bond incorporates more valence electrons.
- metallic character
- a trait to demonstrate how much an element exhibits the common characteristics of metals. This characteristic follows a trend on the periodic table.
- metalloid
- an element as specified on the periodic table to be so. Metalloids have some characteristics of metals and some of nonmetals. All metalloids are solid at room temperature.
- molecule
- the smallest particle of a substance which still displays the properties of that substance. An elemental molecule contains only one element. A molecule of a compound contains different elements.
- neutron
- a neutral particle found in the nuclei of atoms
- nonmetal
- an element as specified on the periodic table to be so. Nonmetals are poor conductors. Nonmetals in a solid state are brittle.
- nonpolar
- no charge difference between any atoms in a molecule because the electrons are distributed evenly
- nucleus
- a cluster of particles in the center of an atom. The protons and neutrons in the nucleus are orbited by electrons.
- oxidization
- a reaction in which atoms or ions of an element experience an increase in oxidation state (meaning a loss of electrons)
- oxidation state, or number
- the charge assigned to each atom in a compound or ion indicating the general distribution of electrons. An oxidation number has no physical meaning; it is only assigned based on an atom's electronegativity relative to other atoms to which it is bonded in a given molecule.
- oxidizing agent
- a substance that has the potential to cause another substance to be oxidized. This agent gains electrons in a redox reaction and therefore is the reduced substance.
- period
- a row of elements on the periodic table. These rows are useful for following trends and determining electron shells on atoms.
- periodic law
- the properties of chemical elements are a periodic function of the atomic numbers
- polar
- where a molecule or ion exhibits a slight positive charge to one end and slight negative charge to the other. Polarity is caused by an uneven distribution of electrons.
- polyatomic molecule
- a molecule containing three or more atoms
- proton
- a positively charged particle found in the nuclei of atoms
- quantum numbers
- four numbers that describe the "address" of an electron in an atom according to a mathematical model. The numbers reveal the electron's energy level, orbital shape and orientation, and the direction of its spin.
- radioactive
- a characteristic in which an element or compound gives off radiant energy in the form of alpha, beta, or gamma rays (radioactivity) through the decomposition or destruction of individual atoms
- reactivity
- a concept similar to metal activity
- redox reaction
- abbreviation for reduction/oxidation reaction, a reaction in which elements undergo changes in oxidation number
- reducing agent
- a substance that has the potential to cause another substnace to be reduced. This agent loses electrons in an redox reaction and therefore is the oxidized substance.
- reduction
- a reaction in which atoms or ions of an element experience a decrease in oxidation state (meaning a gain of electrons)
- s-block, p-block, d-block, f-block
- sections of the periodic table used for easy reference and when writing electron configurations for atoms. The s-block is the first two columns of the table (groups 1 and 2) and helium. The p-block is the last six columns of the table (groups 13 through 18) minus helium. The d-block is the middle of the table (groups 3 through 12). The f-block includes the elements in the Lanthanide and Actinide series.
- solid
- one of the four states of matter. Solids have a definite shape, volume and melting point, are significantly affected by intermolecular forces, are incompressible and diffuse slowly.
- soluble
- the ability to be dissolved in a liquid
- tensile strength
- the ability to resist breaking when pulled
- valence electrons
- those negatively charged particles in the outermost electron shell of an atom. These electrons are those lost or shared in bonding. The valence shell may also gain electrons in bonding.
A B C D E F G H I L M N O P Q R S T V
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