Science

atomic mass unit

-unit of measurement for atomic particles -one-twelfth the mass of a carboun atom containing six protons and six neutrons

chemical symbol

a letter and possibly two stand for an element

elements

abbreviated in scientific shorthand-first letter or two of element's name

isotopes

atoms of the same element with different numbers of neutrons

hydrogen and helium

building blocks of other naturally occurring elements

elements are organized in the periodic table

by increasing atomic number

atomic mass

composed mostly of the protons and neutrons in the nucleus

neutrons

dont have an electrical charge

number of neutrons

equal to mass number minus atomic number

protons

have electrical charge of 1+

electrons

have electrical charge of 1-

periods

horizontal rows of wlwments that contain increasing numbers of protons and electrons -twll us the number of energy levels or shells and the number of electrons on each energy level for every element on that row

Henry G.J. Moseley

in 1913 arranged the elements by atomic number rather than atomic mass

Dimitri Medeleev

in the late 1800s evised the first periodic table based on atomic mass

quarks

smaller particles that make up protons and neutrons

atom

smallest piece of matter that still gas the properties of the element

supenovas

spread heavier elements throughout the universe

atomic number

the number of protons in an atom; number of protons also identifies the element -this number tells exactly what the element or atom is. It connot be changed or it will be antother element

mass number

the sum of the number of protons and neutrons in the nucleus of an atom

average atomic mass

the weighted-average mass of an element's isotopes

groups or families

vertical columns in the periodic table of elements with similar properties -18 -elements with the same valence number

metal, nonmetals,or metalloids(semimetals)

what elements are classified as