Chapter 4

Question 1

atom

Answer 1

the smallest unit of an element that maintains the properties of that element

Question 2

electron

Answer 2

a subatomic particle that has a negative charge

Question 3

nucleus

Answer 3

in physical science, an atom’s central region which is made up of protons and neutrons

Question 4

electron cloud

Answer 4

a region around the nucleus of an atom where electrons are likely to be found

Question 5

proton

Answer 5

a subatomic particle that has a pos

Question 6

atomic mass unit

Answer 6

a unit of mass that describes the mass of an atom or molecule

Question 7

neutron

Answer 7

a subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen.

Question 8

atomic number

Answer 8

the number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element

Question 9

isotope

Answer 9

an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass)

Question 10

mass number

Answer 10

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

Question 11

atomic mass

Answer 11

the mass of an atom expressed in atomic mass units

Question 12

John Dalton

Answer 12

developed his atomic theory from observations gathered from many experiments

Question 13

modern atomic theory

Answer 13

is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms.

Question 14

Democritus

Answer 14

came up with the term atom

Question 15

Niels Bohr

Answer 15

proposed electrons move around the nucleus in certain paths or energy levels

Question 16

Rutherford

Answer 16

proposed a tiny positively charged part called nucleus

Question 17

Thomson

Answer 17

discovered negatively charged particles that are now known as electrons