History of Atoms

make up everything

Atoms....• Are the smallest particles into which an

element can be divided and will remain the same substance

• Make up elements – (which combine to form compounds)

• often called the building blocks of matter

Atoms....• Were not seen prior to 1981 when the

scanning tunneling microscope was invented

• comes from the Greek word atomos, meaning indivisible

However…The atomic theory has been around for more

than 2000 years!

Reminder....

A Theory is....• an explanation for a broad range of

hypotheses and observations that have been supported by testing

The History of the Atom

•Starting in Greece with Democritus

The History of the Atom

Democritus Proposed

(around 440BC)• that if a person continued to cut a coin in half over and over again, they would eventually end up with an uncuttable piece

• the name for the atom• all atoms are small hard particles made

form a variety of shapes and sizes• all atoms are moving and made from

different materials joining together

Aristotle disagrees

(around 300BC)• Stating particles could be divided indefinitely

Its All Greek To

Me!

Meet Aristotle & Democritus

Next stop.......•Great Britain for the Atomic Theory

What are combined

elements with constant mass ratio called?

(hint from chapter 4)

COMPOUNDS!!

Pop Question???

Dalton States(around 1700s)•Atomic Theory:

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

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

• Atoms join with other atoms to make new substances

Meet Dalton

• discovered that there were small particles inside the atom, therefore, the atom could be divided into smaller parts!

Thomson Discovers

Thompson Experimen

ted

Cathode-ray tube

Thompson concluded...• The beam was made of particles with a

negative electric charge

• Which Thompson called corpuscles and led him to believe…• that corpuscles are present in every type of atom

• all corpuscles are identical

Thompson concluded...

• revises atomic theory to account for the presence of electrons (the negatively charged corpuscles or particles he found in his experiment)

• also figures out that since an atom has no charge overall, there must be something with a positive charge within the atom to balance the charges.

• This model became known as the plum pudding model because it looked like a popular dessert at the time. We might call it the chocolate chip ice cream model today!

Thompson’s model

• Comes up with his own model of the atom after the gold foil experiment

Rutherford changes theory

Meet Rutherford

• suggested that electrons travel around the nucleus in definite paths

• that the electrons could jump between paths

Bohr suggests... (Who worked with Rutherford)

Jumping Electrons

• The exact movement of an electron cannot be predicted but, according to current theory, there are regions of the atom where the electrons are more likely to be found. These are called electron clouds.

Current Theory

Current Theory