1. chapter 4
Atoms

2. What is a model?

3. Uses familiar ideas to explain unfamiliar facts observed in nature.
Model
Uses familiar ideas to explain unfamiliar facts observed in nature.
It can be changed if you get new info.

4. You get a mental picture or a model of the object.
INDIRECT EVIDENCE
Evidence you get about an object without actually seeing or touching the object.
You get a mental picture or a model of the object.

5. Greek Model
In the 5th century BC, Democritus believed that matter could be divided into smaller & smaller pieces forever until you got to the smallest possible piece called an atom (uncuttable).

6. Daltons Model
In 1803, Dalton published his atomic theory from studying weather & the composition of air.

7. _____ _ _______
1) All matter is made of atoms 2) Different elements have different kinds of atoms 3) Compounds are formed by joining atoms of 2 or more elements.

8. Invented the Plum Pudding Model
Thomson's Model
He discovered the electron & figured it was part of an atom.
Invented the Plum Pudding Model
The atom was a positively charged ball with lots of negatively charged electrons stuck into it like “plums in pudding.”

10. In 1908, Rutherford discovered the nucleus.
_________ _ ____
In 1908, Rutherford discovered the nucleus.
He stated that the atom was mostly empty space made up of a positively charged nucleus with negative electrons scattered around it.

12. Rutherford’s Experiment
In his experiment, Rutherford fired a stream of alpha particles at a sheet of gold foil and found that:
Most of the bullets passed right through the gold sheet without changing course which meant that the gold atoms were made up of empty space.

14. 2. Some bullets bounced back from the sheet which meant that like charges repel. The alpha particles were positive so the nucleus must then be positively charged.

15. Bohr fixed up Rutherford’s theory.
Bohr’s Model
Bohr fixed up Rutherford’s theory.
He stated that electrons orbited the nucleus on definite paths like the planets around the sun.

17. The Wave Model
Based on a prediction of where the electrons actually are using math formulas.
Basic idea of waves.

18. Subatomic Particles- particles smaller than an atom
4-2 Structure of Atom
Subatomic Particles- particles smaller than an atom
3 Main Subatomic Particles: Protons, Neutrons, Electrons

19. Nucleus The tiny center of atom
99.9% of atom’s weight is the nucleus but it is 100,000 times smaller than the entire atom.
Like a bee in Yankee Stadium

20. Protons
Positively Charged particles (+)
Found in nucleus
Weighs 1 AMU

21. Neutrons
Neutral particles
Found in nucleus
Weighs 1AMU+

22. AMU
ATOMIC MASS UNIT
Special unit used to measure the mass of subatomic particles.
1 proton = 1AMU

23. Atomic Number
Number of protons in nucleus of atom
Determines what the element is

24. Hydrogen’s Atomic number is 1 = 1 proton
Carbon’s Atomic Number is 6 = 6 protons

25. Isotopes
Atoms of same element that have the same number of protons but a different number of neutrons
C12- C14- difference-
2 more neutrons

26. MASS NUMBER Sum of protons & neutrons
distinguishes one isotope from another
Carbon = Mass# 12
6P + 6N= 12 total.

27. Uranium238
146N + 92P = Uranium235
143N + 92P = 235

28. Atomic Mass
Average mass of all isotopes of that element, usually a decimal located on the bottom of each card.
Atomic mass of carbon=12.011

29. Electrons Number of protons = number of electrons outside nucleus.
Electron fills cloud. Electrons can be anywhere within the space around nucleus

30. Electrons are arranged in energy levels according to how much energy they contain
Electrons with lowest energy are in level closest to nucleus.

31. Electrons with high energy are in levels farther from nucleus.
Each level can only hold so many electrons: 1st-2 2nd-8 3rd th th-18

32. Chemical makeup
Properties of elements depend on how many electrons are in the various energy levels.
Bonding: some do/some don’t
Quarks-3particles that make up protons & neutrons