1. Atoms and Molecules
Parts of the Atom

2. What is an atom?
Democritus, a Greek philosopher theorized that at some point a substance can no longer be divided. He called this atomos, greek for indivisible.
Atom = the smallest part, indivisible.

3. What is Atomic Theory?
Atomic theory states that atoms are the building blocks of all matter.
Matter is any material substance that occupies space and has weight.
Matter makes up ALL the observable universe

4. Parts of the atom
Atoms have a nucleus and an outer cloud that are made up of smaller parts called subatomic particles.
Protons
In the Nucleus
Neutrons
In the electron cloud Electrons

5. Subatomic Particles
Proton = the positive “+” charged particle in the nucleus of an atom.
Protons have mass.
Electron = the negative “-” charged particle orbiting around the nucleus of an atom.
Electrons have very little mass.
Neutron = the neutral (no charge) particle in the nucleus of an atom.
Neutrons have mass

6. What do atoms look like?

11. What is matter?

12. Subatomic Particle Comparison
Relative Mass
Electrical Charge
Location in the atom
Proton
1 amu
1 +
Part of the nucleus
Neutron
None
Electron
amu
1 -
Moves around the nucleus in the electron cloud

13. Models: Why use them?
Models are used to help us see, and understand, something that can not be observed directly, or easily.
Models help us understand how something is built or how something works.

14. What is a model?

15. What is a model?
A model is a description or physical representation of something.
We must make mental models for things that we can not see.

16. Scientific Models

17. Early Models of the Atom
J. J. Thomson
John Dalton
Neils Bohr
Ernest Rutherford

18. Early Models of the Atom
John Dalton
J. J. Thomson
Ernest Rutherford
Neils Bohr

19. Evolution of Atom Models

20. The Electron Cloud Model

21. Atomic Number
Atomic number is the number of protons in the atom of an element.
The atomic number of an element is found using the Periodic Table of the Elements.

22. Atomic Mass
Atomic mass is the mass of the atom, or how much the atom weighs.
Different atoms have different masses because of the different number of protons and neutrons.
Atomic mass is equal to the number of protons plus the number of neutrons
Atomic mass = protons + neutrons

23. Atom Terms

24. Atoms Form Elements An element is the simplest form of a substance.
If we break an element down any smaller we get protons, neutrons and electrons in known proportions. If we do this we lose the characteristics of the substance.

25. Atoms of Elements Combine to Form Molecules
Atoms will combine with other atoms and form molecules.
Examples are:
Oxygen + Oxygen = O2 (oxygen molecule)
Hydrogen + Oxygen = H2O (water molecule)
Carbon + Hydrogen + Oxygen = C6H12O6 (sugar molecule)

26. What are Molecules? A molecule is two or more atoms joined together.
Example is water, H2O

27. What do molecules look like?

28. Salt Molecule

29. What Are Subatomic Forces?
Subatomic forces are forces within the atom that are responsible for holding the atom together.
Subatomic forces explain the behavior of the subatomic particles.
The four subatomic forces are:
Electromagnetic force
Strong force
Weak force
Gravity

30. What is Electromagnetic Force?
Electromagnetic force is a force of attraction.
It can either attract or repel the particles on which it acts.
If the particles have opposite charges, such as a proton (+) and an electron (-), the electromagnetic force is a force of attraction.
If the particles have the same charges, such as two protons (+) (+), the electromagnetic force is a force of repulsion.

32. What is Strong Force?
Strong force is the force that “glues” the protons together to form the nucleus of an atom.
The strong force opposes the electromagnetic force.

33. What is Weak Force?
The weak force is the key to the power of the sun, it is responsible for a process called radioactive decay.
During radioactive decay a neutron in the nucleus changes into a proton and an electron.

34. What is Gravity?
Gravity is the force of attraction exerted between all objects in nature.
Gravity is the weakest force known in nature.

35. Atomic Structure Review
Parts of the atom:
Subatomic particles
Proton: “+” charge found in the nucleus
Neutron: no charge found in the nucleus
Electron: “-” charge found outside nucleus in electron cloud
Atomic number = # of protons
Atomic mass = protons + neutrons
Models of the atom:
Dalton
Thomson
Rutherford
Bohr
Electron Cloud