Basic Atomic Structure and History

Atoms

• Smallest piece of matter that is still considered an element.

• The building blocks of molecules.

• A type of subatomic particle.

• A form of energy in physics.

Atomic Mass

• The total number of electrons in an atom of a specific element.

• The number of protons and neutrons found in an atom of a specific element.

• The average mass of all isotopes of an element.

• The mass of an atom measured in atomic mass units (amu).

Niels Bohr (1913)

• Said electrons move in circular orbits, or energy levels, around the nucleus.

• Proposed that electrons are found in fixed paths around the nucleus.

• Claimed that electrons have no defined position until measured.

• Suggested that electrons can exist in multiple states simultaneously.

Isotope

• Different versions of an element that have the same # of protons, BUT different # of neutrons.

• Elements that have the same number of neutrons but different numbers of protons.

• Atoms that have the same mass number but different atomic numbers.

• Different elements that have identical chemical properties.

5

• 3

• 5

• 7

• 4

Democritus (400 BC)

• First used the word 'atoms' to describe small solid objects that cannot be divided, created, or destroyed.

• Proposed that all matter is made up of four elements: earth, water, air, and fire.

• Believed that the universe is infinite and contains an infinite number of worlds.

• Introduced the concept of the atom as a fundamental unit of life.

Nucleus

• Center of the atom that is made up of protons and neutrons.

• The outer shell of an atom where electrons are found.

• A type of subatomic particle that has no charge.

• The smallest unit of an element that retains its properties.

Strong Force

What keeps protons (of like charge) together in the nucleus?

• Electromagnetic Force

• Weak Force

• Gravitational Force

• Strong Force

Quark

• Tiny particles that make up protons and neutrons.

• Large particles found in the nucleus of an atom.

• Electrons that orbit around the nucleus.

• Fundamental forces that hold atoms together.

James Chadwick (1932)

• Discovered the neutral neutrons in the nucleus.

• Proved that electrons are negatively charged particles.

• Identified the nucleus as the center of the atom.

• Developed the first periodic table of elements.