Chemistry - Atoms (copy)

Unit 2

atom

the smallest particle of an element

atomic mass

a value that depends on the distribution of an elements isotopes in nature and the masses of those isotopes

atomic mass unit(amu)

one twelfth the mass of a carbon - 12 atom

dalton’s atomic theory

the first theory to relate chemical changes to events at the atomic level

electron

a negatively charged subatomic particle

cathode-ray

a stream of electrons produced at the negative electrode (cathode) of a tube containing a gas of a low pressure

group

a vertical column of elements in the periodic table; the constituent elements of a group have similar chemical & physical properties

isotopes

atoms of the same element that have the same atomic number but different atomic masses due to a different number of neurons

mass number

the total number of protons and neurons in the nucleus of an atom

neutron

a subatomic particle with no charge & a mass of one amu; found in the nucleus of an atom

nucleus

the tiny; dense central portion of an atom, composed of protons & neutrons

period

a horizontal row of elements in the periodic table

period table

an arrangement of elements in which the elements are separated into groups based on a set of repeating properties

proton

a positively charged subatomic particle found in the nucleus of an atom