Historical Models

20. Which of these best describes the particle motion taking place as gas is exposed to freezing temperatures?◦ A) The particles decrease in speed.◦ B) The particles move with more force.◦ C) The motion of the particles becomes

random.◦ D) The motion of the particles is unchanged.

21. Which of these substances is an element?◦ F) Steel◦ G) Chlorine◦ H) Plastic◦ J) Sugar

Science Starter

Molecule 1

Molecule 2

Molecule 3

Molecule 4 (can you make more?)

Total number of molecules you can make

Hydrogen Atoms only

Hydrogen and Oxygen

Carbon and Hydrogen

Draw a chart in your lab notebook

All matter is made up of individual particles called atoms, which cannot be divided.

All elements are composed of atoms. All atoms of the same element have the

same mass, and atoms of different elements have different masses.

Compounds contain atoms of more than one element.

In a particular compound, atoms of different elements always combine in the same way.

John Dalton’s Atomic Theory

A representation of something

Ex. The tennis balls of science◦ What do they represent?◦ Are they actually what they represent?◦ Usually a simplified version of something complex

What is a model?

Small Solid Spherical Indivisible

Dalton’s Atomic Model

Positive and Negative Charges are dispersed throughout the atom

Atoms have charge Electrons are stuck

in the atom like raisins are stuck in a bowl of plum pudding

JJ Thomson’s Plum Pudding Model

JJ, Plum Pudding, Chocolate Chip

Ernest Rutherford In 1906 he decided

to test the plum pudding model.

He shot alpha particles at gold foil. ◦ Some passed through

the “empty” space outside the nucleus

◦ Some bounced off the nucleus of the atom and back at the screen

Dense, positively charged nucleus

Empty space for most of atom

Peach Pit Model (Rutherford)

Dense nucleus Electrons are found

in distinct energy levels that are only found a specific distance from the nucleus

Bohr Model

Dense nucleus Space outside

nucleus where electrons are most likely to be found

Do NOT follow fixed paths like in the Bohr Model

“Fan” Model

Modern Atomic Model