Alkali metal
The Group 1 elements, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr) react with cold water for form strongly alkaline hydroxide solutions, and are referred to as "alkali metals". Hydrogen is not considered an alkali metal, despite its position on some periodic tables.
Alkaline earth metal
The Group 2 elements, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) form alkaline oxides and hydroxides and are called "alkaline earth metals".
Atom
A particle of matter indivisible by chemical means. It is the fundamental building block of elements.
Atomic mass
Approximately the sum of the number of protons and neutrons found in the nucleus of an atom.
Atomic number
The number assigned to each element on the basis of the number of protons found in the element's nucleus
Bohr model
A model of the structure of the atom developed by Niels Bohr in 1913, depicting the atom as a small, positively charged nucleus surrounded by electrons in orbit - similar in structure to the solar system. It has since been proven that electrons, protons and neutrons are made up of smaller particles, but his model is adequate for explaining electrical circuits.
Conductivity
A measure of the transfer of heat through a stationary substance; also the movement of ions or electrons through a material.
Covalent compounds
A compound in which the atoms that are bonded share electrons rather than transfer electrons from one to the other. While ionic compounds are usually formed when metals bond to nonmetals, covalent compounds are formed when two nonmetals bond to each other.
Density
Mass per unit volume.
Electron
The negatively charged fundamental particles present in ordinary matter, surrounding the nucleus.It has a charge of negative electricity equal to about 1.602 × 10−19 coulomb and having a mass when at rest of about 9.109 × 10−31 kilogram or about that of a proton.
Element
Any of the fundamental substances that consist of atoms of only one kind and that singly or in combination constitute all matter.
Halogens
Any of the five elements fluorine, chlorine, bromine, iodine, and astatine that form part of group VIIA of the periodic table and exist in the free state normally as diatomic molecules
Ionic compounds
Chemical compounds that consist of charged ions with opposite charges. They are generally solids with high melting points that conduct electrical current. The positively charged ion is usually a metal ion and the negatively charged ion is non-metallic element or molecule.
Mass
A basic property of matter. It is a measure of an object's resistance to acceleration. It is amount of material present in an object. In an Earth environment this quantity is often directly compared to weight.
Melting/boiling point
Melting: the temperature below which a liquid turns into a solid
Boiling: the temperature at which a liquid boils at sea level, when bubbles of vapor are generated
Molecule
The smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms
Multiple ion charge
An ion is an atom or molecule that has acquired a charge by either gaining or losing electrons. An atom or molecule with missing electrons has a net positive charge and is called a cation*; one with extra electrons has a net negative charge and is called an anion
Metal
A substance that conducts heat and electricity, is shiny and reflects many colors of light, and can be hammered into sheets or drawn into wire. Metals lose electrons easily to form cations*. About 80% of the known chemical elements are metals.
Metalloid
An element with both metallic and nonmetallic properties. Examples are silicon, arsenic, and germanium.
Neutron
An uncharged elementary particle that has a mass nearly equal to that of the proton and is present in all known atomic nuclei except the hydrogen nucleus
Noble gases
Any of the elements of Group 18, which includes helium, neon, argon, krypton, xenon, radon, and element 118. These elements are referred to as "inert" or "noble" because they do not easily form compounds with other elements.
Non-metal
A substance that conducts heat and electricity poorly, is brittle or waxy or gaseous, and cannot be hammered into sheets or drawn into wire. About 20% of the known chemical elements are nonmetals.
Polyatomic ions
Charged molecules. The atoms within a polyatomic ion are usually very tightly bound together, so the ion retains its identity within ionic compounds and over the course of many chemical reactions.
Proton
An elementary particle found in the atomic nucleus with a positive charge equal and opposite that of the electron.
State
There are three common states of matter: gases, liquids, and solids. States of matter differ in the way the molecules are arranged at the molecular level, but not in the structure of the molecules themselves. Other states (the plasma and Bose-Einstein condensate states) are uncommon on Earth.
Subatomic particles
A body having finite mass and internal structure but negligible dimensions
Volume
The amount of 3-dimensional space occupied by an object. "Specific volume" is the volume of a unit mass of substance. For example, the specific volume of water at 4°C is 1.00000 mL/g. Specific volume is the reciprocal of density.
RESOURCES
Classroom Strategies for Teaching Science Definitions
