1. Atomic Theory and the Atom
Chapter 11

2. Atomic Theory History Atomic Models
istry/atoms/

3. Atomic History Democritus- 440 B.C. Aristotle- 338-322 B.C
He proposed that if you kept cutting something in half you would eventually end up with an “uncutable” particle. Which he called an atom
Greek: Atomos - indivisible
Aristotle B.C
He disagreed with Democritus. He believed you would never end up with an indivisible particle.

4. Dalton- 1808
In search of understanding why elements combine in specific ratios he discovered through his experiments that this happens because they are made of individual atoms.
His theory states 3 things
1- Atoms are small and cannot be
created, divided or destroyed.
2- Atoms of the same element are all alike
3-Atoms join with other atoms to make
new substances

5. Thomson discovered electrons
Thomson discovered electrons. His plum-pudding model described the atom as a lump of positively charged material with negative electrons scattered throughout.
Rutherford discovered that atoms contain a small, dense, positively charged center called the nucleus.
• Bohr suggested that electrons move around the nucleus at only certain distances.
According to the current atomic theory, electron clouds are where electrons are most
likely to be in the space around the nucleus.

6. Rutherford
Gold foil
Experiment

7. Atomic Structure

8. The Atom Atoms are extremely small. Atoms contain a nucleus.
Atoms are made of subatomic particles
Protons
Neutrons
Electrons

9. Positively charged particles (+). Found in the nucleus.
Protons
Positively charged particles (+).
Found in the nucleus.
All protons are identical
Each proton= 1 amu (atomic mass unit)
Every atom of the same element has the same number of protons.

10. Particles that have no charge Found in nucleus
Neutrons
Particles that have no charge
Found in nucleus
All neutrons are identical
Protons & Neutrons are the most massive particles in the atom but
located in a very small area (nucleus)

11. Electrons Negatively charged particles (e-)
Located outside of the nucleus in rings or levels called atomic clouds
Their mass is so small that it is usually considered zero.
It takes more than 1,800 electrons to equal the mass of one proton.
However electrons occupy most of an atoms volume.

12. Parts of the atom

13. Some things to remember:
In an atom, the number of protons equals the number of electrons. As a result, the positive charge from protons equals the number of electrons which makes the atom neutral.
All atoms of an element have a different atomic number.

14. Tells us the number of protons in an atoms nucleus
Atomic mass unit = Protons + Neutrons

15. Atomic Mass
Atoms are too small to be measures in everyday untis of mass (grams)
Scientist use units known as Atomic mass units (amu)
A proton or a neutron has a mass equal to about 1/1000th
Atomic Mass is equal to the number of protons and neutrons in an atom.

17. Isotopes
m/science/matterandche mistry/isotopes/
Isotopes are atoms that have the same number of protons but different numbers of neutrons.
Each element has a limited number of isotopes that occur naturally.
Some isotopes can be unstable and change it’s composition. We call these radioactive.

18. ISOTOPES
Isotopes of hydrogen and uranium are shown as examples of the isotope notation method
Unlike other elements' isotopes, the two heavy isotopes of hydrogen have their own names.
Isotopes are atoms that have the same number of protons but have different number of neutrons

19. Arrangement of Electrons
The first ring can only hold 2 electrons
The second ring can hold up to 8 electrons
The third ring can hold up to 8 electrons
Fourth can hold up to 18
Principle quantum model 2, 8,18, 32. Electron Capacity = 2n2
The variable n represents the Principal Quantum Number, the number of the energy level in question.
P = N=
Valence Shell: last orbital where the “giving” and “receiving” of electrons take place CHEMICAL REACTIONS

21. Talk about: Is it an Element or Ion? Ions and valence Electrons

22. • The four forces at work in an atom are gravity, the electromagnetic force, the strong
force, and the weak force.

23. Bohr Model and Flame Lab