1. Do First
Actions: Turn in yesterday’s electron, proton, and neutron practice if you did not get it stamped
Questions:
If a neutral atom has an atomic mass of 20 and 15 neutrons. What is the identity of this element?
If a neutral atom has an atomic mass of 20 and 15 electrons. What is the identity of this element?

2. Agenda Atomic Theory Notes Bohr Model Practice
But It’s Natural Reading

3. Atomic Theory

4. Democritus (460 – 370 B.C.) Greek Philosopher
First person to propose the idea that matter was not infinitely divisible
Believed that matter was made up of tiny individual particles called atomos, from which the English word atom is derived
Believed that atoms could not be created, destroyed, or further divided.

5. John Dalton (1766 – 1844)
Revived and revised Democritus’s ideas based on the results of scientific research he conducted.
In many ways, Democritus’s and Dalton’s ideas are similar

6. John Dalton (1766 – 1844) Dalton’s proposed ideas:
Matter is composed of extremely small particles called atoms
Atoms are indivisible and indestructible*
Atoms of a given element are identical in size, mass, and chemical properties*
In a chemical rxn, atoms are separated, combined, or rearranged.
*we now know that these are not accurate

7. J.J. Thomson (1856 – 1940)
Discovered (identified) electrons using cathode ray tube
(3 minutes)
Developed “plum pudding” model of atoms: Electrons (raisins) scattered through a sphere of positive charge (pudding)
Nothing was known about a nucleus at this time

8. J.J. Thomson (1856 – 1940) + + + + + + + + +

9. Ernest Rutherford (1871 – 1937)
Conducted an experiment to see how positively charged particles would interact with solid matter
In his “Gold Foil Experiment” he shot a narrow beam of alpha particles at a piece of thin gold foil.

10.
Rutherford
Most of the radiation went straight through the foil (like he expected), but sometimes the radiation ricocheted

11. Ernest Rutherford (1871 – 1937)
Expected Results
Actual Results

12. Ernest Rutherford (1871 – 1937)
He concluded that the atom is mostly empty space through which the electrons move.
Most of all the atom’s positive charge and almost all of its mass were contained in a tiny dense region in the center of the atom, which he called the nucleus.

13. James Chadwick (1891 – 1974)
Compared the amount of charge in an atom vs. its mass and it didn’t add up… he thought that there MUST be something else in there…
From this, he discovered (identified) the neutron

14. Bohr Developed planetary model of atom
Electrons orbit the nucleus in energy levels (shells)
Even though this model isn’t really correct, it is still helpful

15. Bohr

16. Electron Cloud Model
Electrons are found in areas of probability around the nucleus
Energy levels divided into sublevels
Sublevels divided into orbitals

17. Electron Cloud Model
Nucleus
Electrons

18. DYL 1. Who proposed the plum pudding model?
2. Identify the element that has the Bohr model below?