2.  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

3. 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

4.  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.

5.  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

6.  Small  Solid  Spherical  Indivisible

7.  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

9.  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

10.  Dense, positively charged nucleus  Empty space for most of atom

11.  Dense nucleus  Electrons are found in distinct energy levels that are only found a specific distance from the nucleus

12.  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