Understanding the Atom

Democritus believed that the universe was made of empty space and __________ .

• molecules

• compounds

• elements

• atoms

What nineteenth century scientist designed the atomic theory of matter?

• J.J. Thomson

• Ernest Rutherford

• John Dalton

• Isaac Newton

Why did J.J. Thomson conclude that cathode rays were made up of small particles that had mass?

• They were bent by a magnet.

• The metal plates in his experiment had no net charge.

• Some of the rays changed direction and bounced back.

• He could see individual particles traveling from the negatively charged plate to the positively charged plate.

Tags

NGSS.MS-PS1-1

The small, negatively charged particles discovered by J.J. Thomson are called __________ .

• protons

• neutrons

• electrons

• alpha particles

James Chadwick named the uncharged particles in the atomic nucleus

• protons

• electrons

• neutrons

• alpha particles

Atoms of the same element that have different numbers of neutrons are called __________.

• isotopes

• metals

• nonmetals

• metalloids

An element's atomic number is the number of __________ in the nucleus of each atom of that element.

• neutrons

• protons

• electrons

• positrons

Most of an atom's mass is contained in __________.

• the electron orbits

• the electron cloud

• its outer energy shell

• its nucleus

A(n) __________ is an atom that has gained or lost an electron and is no longer neutral.

• ion

• isotope

• molecule

• compound

__________ is the release of nuclear particles and energy.

• Transmutation

• Atomic half-life

• Nuclear decay

• Carbon dating

Tags

NGSS.HS-PS1-8