LBC Unit 1 and 2 Key Terms Flashcards
Key Term
Definition
hypothesis
A proposed explanation for an observation or scientifi c problem, which can be tested by further investigation.
property
A characteristic or quality of a substance
chemistry
Th e study of substances, their properties, and how they can be transformed; the study of matter and how it can be changed.
matter
Anything that has substance and takes up space; anything that has mass and volume.
mass
A measure of the quantity of matter in an object
volume
Th e amount of space a sample of matter occupies.
meniscus
Th e curvature of the top of a liquid in a container, which is the result of intermolecular attractions between the liquid and the container
density
Th e measure of the mass of a substance per unit of volume, oft en expressed as grams per milliliter, g/mL, or grams per cubic centimeter, g/cm3 .
intensive property
A characteristic, such as boiling point or density, that does not depend on the size or amount of matter and can be used to identify matter.
extensive property
A characteristic, such as volume or mass, that is specifi c to the amount of matter and therefore changes if the quantity of the substance changes.
element
A unique substance that cannot be broken down into simpler substances through physical or chemical processes. Elements serve as the building materials of all matter.
chemical symbol
A one- or two-letter representation of an element. Th e fi rst letter is always uppercase. If there is a second letter, it is lowercase.
compound
A pure substance that is a chemical combination of two or more elements in a specifi c ratio.
chemical formula
A combination of element symbols and numbers representing the composition of a chemical compound.
phase
Th e physical form of matter such as the solid, liquid, or gaseous state
aqueous
A solution in which water is the dissolving medium or solvent.
chemical change
A transformation that alters the composition of one or more substances such that one or more new substances with new properties are produced.
chemical reaction
A transformation that alters the composition of one or more substances such that one or more new substances with new properties are produced.
reactivity
Th e tendency of an element or compoundto combine chemically with other substances, as well as the ease or speed of the reaction.
average atomic mass
Th e weighted average of the mass of the isotopes of an element.
atomic mass unit (amu)
Th e unit used for expressing atomic mass. 1 amu 5 1.66 3 10224 g, the mass of one hydrogen atom. Th is is 1/12 the mass of a carbon-12 atom.
periodic table of the elements
A table with elements organized in order of increasing atomic number and grouped such that elements with similar properties are in vertical columns.
atomic number
Th e consecutive whole numbers associated with the elements on the periodic table. Th e atomic number is equal to the number of protons in the atomic nucleus of an element.
group
A vertical column on the periodic table, also called a family. Elements in a group have similar properties.
alkali metal
Th e elements in Group 1A on the periodic table, except for hydrogen.
alkali earth metal
Th e elements in Group 2A on the periodic table
halogen
Th e elements in Group 7A on the periodic table.
nobel gas
Th e elements in Group 8A on the periodic table. Noble gases are known for not being reactive.
period
Th e elements in a horizontal row on the periodic table.
main group elements
Th e elements in Groups 1A to 7A on the periodic table.
transition elements
Th e elements in Groups 1B to 8B on the periodic table.
lanthanides
A series of elements that follow lanthanum in Period 6 of the periodic table; they are typically placed separately at the bottom of the periodic table.
actinides
A series of elements that follow actinium in Period 7 of the periodic table and that are typically placed separately at the bottom of the periodic table.
metal
An element that is generally shiny and malleable and an excellent conductor of heat and electricity. Metals are located to the left of the stairstep line on the periodic table.
nonmetal
An element that does not exhibit metallic properties. Nonmetals are often gases or brittle solids at room temperature. Nonmetals are poor conductors of heat and electricity and are located to the right of the stair-step line on the periodic table.
metalloid
An element that has properties of both metals and nonmetals. Metalloids are located along the stair-step line of the periodic table.
atom
Th e smallest unit of an element that retains the chemical properties of that element and can exist as a separate particle.
atomic theory
A theory that states that all matter is made up of individual particles called atoms.
model
A simplifi ed representation of a real object or process that facilitates understanding or explanation of that object or process.
nucleus
Th e dense, positively charged structure composed of protons and neutrons that is found in the center of an atom.
proton
A positively charged particle located in the nucleus of an atom. Th e mass of a proton is almost exactly equal to that of a neutron, about 1 amu.
neutron
A particle that is located in the nucleus of an atom and does not have an electric charge. Th e mass of a neutron is almost exactly equal to that of a proton, about 1 amu.
electron
An elementary particle with a negative charge that is located outside of the nucleus of an atom. It has a mass of about 1/1838 amu.
isotope
Atoms of the same element that have diff erent numbers of neutrons. Th ese atoms have the same atomic number but diff erent mass numbers
mass number
h e sum of the number of protons and neutrons in the nucleus of an atom.
average atomic mass
Th e weighted average of the mass of the isotopes of an element.
nuclear reaction
A process that changes the energy,composition, or structure of an atom’s nucleus.
radioactive decay
Spontaneous disintegration of an atomic nucleus accompanied by the emission of particles and radiation. A radioactive substance will decay with a specifi c half-life.
alpha decay
A nuclear reaction in which an atom emits an alpha particle consisting of two protons andtwo neutrons. Alpha decay decreases the atomicnumber of an atom by 2 and the mass number by 4.
alpha particle
A particle made of two protons and two neutrons, equivalent to the nucleus of a helium atom.
beta decay
A nuclear reaction in which a neutron changes into a proton and an electron, and the atom emits a beta particle, which is the electron. Beta decay increases the atomic number of the atom without changing the mass.
beta particle
An electron emitted from the nucleus of an atom during beta decay