Atoms

Distinguish between atoms and

molecules.

In the beginning…

Democritus - Greek philosopher (470-380 B.C.)(di MAHK ruh tuhs)

His thought - He proposed that matter could NOT be divided into smaller pieces forever; you would eventually end up with a particle that could not be cut

Claim - Matter was made up of small, hard particles that he called “atomos”

atomos, or atom, meaning “not able to be divided”

Then came…

John Dalton - A British chemist and school teacher credited for the first atomic theory in 1803

Atomic theory 1. All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.

2. Atoms of the same element are exactly alike, and atoms of different elements are different.

3. Atoms join with other atoms to make new substances called compounds.

Hold up wait a minute…

J.J. Thomson - A British scientist who showed there was a flaw in Dalton’s theory in 1897.

Discovery - Small particles inside the atom. This meant that atoms could be divided into even smaller parts.

Proposal - The existence of negatively charged particles.

- He thought that these negatively charged particles were located throughout an atom like plums in pudding; known as the “plum-pudding model.”

But wait, there’s more…

Ernest Rutherford - In the early 1900’s, Rutherford conducted an experiment to test his former teacher’s theory.

Experiment - Gold Foil Experiment

https://www.youtube.com/watch?v=zUtIrO3fUgg

Results - Rutherford discovered a positively charged particle within the atom, and the atom’s center

Let’s recap!

Atoms a. smallest piece of matter existing in nature

b. smallest piece of a substance that retains the chemical properties of that substance

c. when joined together, create compounds

d. can be divided into smaller particles

- negatively charged

- positively charged

e. has a center

Let’s keep going!!

Niels Bohr - A Danish scientist who improved on Rutherford’s experiment by studying the way atoms react to light in 1913.

Results - These negatively charged particles move around the center in specific layers, or shells. However, they can jump from a path in one level to a path in another.

- Every atom has a specific number of shells.

For real, last person ;-)

James Chadwick - Also worked with Ernest Rutherford

Contribution - In 1932, he discovered particles that did not have a charge.

What’s in a name??

1. The negatively charged particles discovered by J.J. Thomson are known as electrons (-).

2. The positively charged particles discovered by Ernest Rutherford are known as protons (+). And he called the center of the atom the nucleus.

3. The neutrally charged particles discovered by James Chadwick are known as neutrons.

Protons Neutrons

Electron

Cloud

Do you have it?

1. ________________ This small particle of an atom carries a negative charge.

2. ________________ Made up of the protons and neutrons, this part of the atom contains nearly all the mass of the atom.

3. ________________ This small particle of an atom carries a neutral charge.

4. _______________ This refers to the travel of electrons around the nucleus of an atom.

5. _______________ This is a building block of matter.

Molecule

Compound of

two or more

atoms, the

smallest unit of

chemical

compounds.

H H

O