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
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
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.
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
Small Solid Spherical Indivisible
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
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
Dense nucleus Electrons are found in distinct energy levels that are only found a specific distance from the nucleus
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