8th Science Vocab
8th grade science vocab - 1st semester
Terms
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- catalyst
- substance that speeds up a chemical reaction but is not used up by itself or permanently changed
- covalent bond
- chemical bond formed when atoms share electrons
- liquid
- matter with a definite volume but no definite shape that can flow from one place to another
- base
- substance that accepts H+ ions and produces hydroxide ions when dissolved in water
- enzyme
- catalysts that are large protein molecules which speed up reactions needed for your cells to work properly
- freezing
- change of matter from a liquid state to a solid state
- product
- substance that forms as a result of a chemical reaction
- nonmetal
- element that is usually a gas or brittle solid at room temperature and is a poor conductor of heat and electricity
- matter
- anything that takes up space and has mass
- proton
- positively-charged particle in the nucleus of an atom
- alkaline earth metals
- elements in group 2 of the periodic table
- mass number
- sum of the number of protons and neutrons in the nucleus of an atom
- energy level
- the different positions for an electron in an atom
- chemical equation
- shorthand form for writing what reactants are used and what products are formed ina chemical reacton; sometimes shows whether energy is produced or absorbed
- exothermic reaction
- chemical reaction in which heat energy is released
- metal
- element that is malleable, ductile, a good conductor of electricity, and generally has a shiny or metallic luster
- solid
- matter with a definite shape and volume; has tightly packed particles that move mainly by vibrating
- halogen
- elements in group 17 of the periodic table
- chemical property
- characteristic that cannot be observed without altering the sample
- endothermic reaction
- chemical reaction in which heat energy is absorbed
- reactant
- substance that exists before a chemical reaction occurs
- polar bond
- bond resulting from the unequal sharing of electrons
- electron
- negatively-charged particle that exists in an electron cloud formation around an atom's nucleus.
- electron dot diagram
- chemical symbol for an element, surrounded by as many dots as there are electrons in its outer energy level
- surface tension
- the uneven forces acting on the particles on the surface of a liquid
- chemical reaction
- process that produces chemical change, resulting in new substances that have properties different from those of the original substances
- condensation
- the process of changing from a gas to a liquid
- metallic bond
- bond formed when metal atoms share their pooled electrons
- law of conservation of mass
- states that mass is neother created nor destroyed - and as a result the mass of the substances before a physical or chemical change is equal to the mass of the substances present after the change
- activation energy
- minimum amount of energy needed to start a chemical reaction
- sublimation
- the process by which a solid changes directly into a gas
- molecule
- neutral particle formed when atoms share electrons
- representative elements
- elements in groups 1 and 2 and 13 - 18 in the periodoc table that include metals, metalloids, and nonmetals
- saturated
- describes a solution that holds the total amount of solute that it can hold under given conditions
- chemical change
- change in which the composition of a substance changes
- period
- horizontal row of elements in the periodic table whose properties change gradually and predictable
- physical property
- characteristic that can be observed, using the five senses, without changing or trying to change the composition of a substance
- pressure
- force exerted on a surface divided by the total area over which the force is exerted
- solution
- homogeneous mixture whose elements and/or compounds are evenly mixed at the molecular level but are not bonded together
- concentration
- describes how much solute is present in a solution compared to the amount of solvent
- ionic bond
- attraction that holds oppositely charged ions close together
- compound
- a substance produced when elements combine and whose properties are different from each of the elements in it.
- ion
- atom that is no longer neutral because it has gained or lost an electron
- catalyst
- substance that can make something happen faster but is no changed itself
- solute
- substance that dissolves and seems to disappear into another substance
- temperature
- measure of the average kinetic energy of the individual particles of a substance
- rate of reaction
- measure of how fast a chemical reaction occurs
- semiconductor
- element that does not conduct electricity as well as a metal but conducts it better than a nonmetal
- transition elements
- elements in groups 3 - 12 in the periodic table, all of which are metals
- atomic mass
- average mass of an atom of an element; its unit of measure is the atomic mass unit (u), which is 1/12 that mass of a carbon-12 atom
- mixture
- a combination of compunds and elements that has not formed a new substance and whose proportions can be changed without changing the mixture's identity
- aqueous
- solution in which water is the solvent
- substance
- matter that has the same composition and properties throughout
- heat
- movement of thermal energy from a substance at a higher temperature to a substance at a lower temperature
- deposition
- the process by which a gas changes into a solid
- electron cloud
- area where negatively charged electrons, arranged in energy levels, travel around an atom's nucleus
- inhibitor
- substances that slow down a chemical reaction, making the formation of a certain amount of product take longer
- melting
- change of matter from a solid state to a liquid state
- isotope
- two or more atoms of the same element that have different number of neutrons in their nuclei
- precipitate
- solid that comes back out of its solution because of a chemical reaction or physical change
- element
- substance that cannot be broken down into simpler substances
- heterogeneous mixture
- type of mixture where teh substances are not evenly mixed
- pH
- measure of how acidic or basic a solution is, ranging in a scale from 0 to 14
- lanthanide
- the first series of inner transition elements which goes from cerium to lutetium
- chemical formula
- combination of chemical symbols and numbers that indicates which elements and how many atoms of each element are present in a molecule
- homogeneous mixture
- type of mixture where two of more substances are evenly mixed on a molecular level but are not bonded together
- actinide
- the second series of inner transition elements which goes from thorium ot lawrencium
- atomic number
- number of protons in the nucleus of each atom of a given element; is the top number in the periodic table
- physical change
- change in which the form or appearance of matter changes, but not its composition
- Archimedes' principle
- states that the buoyant force on an object is equal to the weight of the fluid displaced by the object
- noble gases
- elements in group 18 of the periodic table
- alkali metals
- elements in group 1 of the periodic table
- neutralization
- reaction in which an acid reacts with a base and forms water and a salt
- indicator
- compound that changes color at different pH values when it reacts with acidic or basic solutions
- solvent
- substance that dissolves the solute
- Pascal's principle
- states that when a force is applied to a confined fluid, an increase in pressure is transmitted equally to all parts of the fluid
- group
- family of elements in the periodic table that have similiar physical or chemical properties
- concentration
- describes how much solute is present in a solution compared to the amount of solvent
- metalloid
- element that shares some properties with both metals and nonmetals
- compound
- pure substance that contains two or more elements
- hydronium ion
- hydrogen ion combines with a water molecule to form a hydronium ion, H3O+
- acid
- substance that releases H+ ions and produces hydronium ions when dissolved in water
- gas
- matter that does not have a definite shape or volume; has particles that move at high speeds in all directions
- buoyant force
- upward force exerted on an object immersed in a fluid
- density
- mass of an object divided by its volume
- viscosity
- a liquid's resistance to flow
- neutron
- electronically-neutral particle that has the same mass as a proton and is foudn in an atom's nucleus
- solubility
- measure of how much solute can be dissolved in a certain amount of solvent
- chemical bond
- force that holds two atoms together
- substance
- matter with a fixed composition whose idenity can be changed by chemical processes but not by ordinary physical processes
- vaporization
- the process by which a liquid changes into a gas