1. History of the Atomic Model How the model of the atom has changed or evolved over time

2. Definition of an Atom The smallest particle of an element The smallest particle of an element There are 2,000 billion billion atoms of oxygen in one drop of water There are 2,000 billion billion atoms of oxygen in one drop of water

3. Atomic Structure Atoms are made up of three basic particles Atoms are made up of three basic particles Protons: Carry a positive charge Protons: Carry a positive charge Neutrons: Carry no charge Neutrons: Carry no charge Protons and neutrons join together to form the nucleus- the central part of the atom Protons and neutrons join together to form the nucleus- the central part of the atom Electrons: carry a negative charge and circle around the nucleus Electrons: carry a negative charge and circle around the nucleus

4. Atomic Structure Electrons Electrons travel around the nucleus in energy shells or orbitals. Electrons travel around the nucleus in energy shells or orbitals. Each orbital can only hold a certain amount of electrons. Each orbital can only hold a certain amount of electrons.

5. Atomic Structure

6. Protons and neutrons have the same mass and are the heaviest part of the atom Protons and neutrons have the same mass and are the heaviest part of the atom Electrons are much smaller, move faster, and give the atom its volume Electrons are much smaller, move faster, and give the atom its volume

7. How have scientists figured this out ????

8. The Greek Model (460-440 BC) Democritus was a Greek philosopher Democritus was a Greek philosopher Matter cannot be divided into smaller and smaller pieces forever. Matter cannot be divided into smaller and smaller pieces forever. The smallest piece called an “atom” The smallest piece called an “atom”

9. Dalton (1790-1807) Atoms are indivisible and indestructible Atoms are indivisible and indestructible Atoms of the same element are exactly alike, atoms of different elements are not Atoms of the same element are exactly alike, atoms of different elements are not Atoms can combine to form more complex compounds Atoms can combine to form more complex compounds

11. Thomson (1887-1898) Called the “Plum Pudding” Model Called the “Plum Pudding” Model Atoms are divisible. Atoms are divisible. Discovered negatively charged particles, called electrons. Discovered negatively charged particles, called electrons. Believed atom was like a positive pudding with negative electrons stuck in it. Believed atom was like a positive pudding with negative electrons stuck in it.

13. Rutherford (1909-1919) Conducted the Gold Foil Experiment Conducted the Gold Foil Experiment Found that atom was mostly empty space with very dense, positive center Found that atom was mostly empty space with very dense, positive center Electrons on the edge of the atom. Electrons on the edge of the atom.

15. Bohr (1913 - 1920) Found that electrons did not move randomly around nucleus, they had definite paths or “orbits” Found that electrons did not move randomly around nucleus, they had definite paths or “orbits” Each orbit only holds a certain number of electrons Each orbit only holds a certain number of electrons Electrons can jump from one orbit to another (quantum jump) Electrons can jump from one orbit to another (quantum jump)

17. Electron Cloud Model (current) Dense nucleus is surrounded by a cloud where the electrons are Dense nucleus is surrounded by a cloud where the electrons are The cloud has energy levels. The cloud has energy levels. Electrons may “jump” back and forth between energy levels. Electrons may “jump” back and forth between energy levels.

19. Whose model is represented by the pictures?