1. Unit 3 Atomic Structure

2. Objective 1
Describe the structure of the atom including: protons, electrons, and neutrons.

3. Atoms and Atomic Theory
Atom - the smallest particle of a given type of matter.
Atomic Theory – the idea that all matter is made up of particles called atoms.
Scale of the Universe website:

4. Early Ideas About Matter
Democritus
400 B.C.
atomos = “indivisible”

5. Modern Atomic Theory Lavoisier
Law of conservation of matter- When a chemical reaction occurs, matter is neither created nor destroyed, but only changed.

6. John Dalton – Father of the Modern Atom
1.) All matter is made of atoms. 2.) All atoms are indestructible and cannot be divided into smaller particles. 3.) All atoms of one element are exactly alike, but they are different from all other elements.

7. Subatomic Particles
Electrons
Protons
Neutrons

8. Electrons
J.J. Thomson – Discovered the electron using a cathode ray tube.
Symbol: e-
Mass = 1/1837 amu
1 amu ~ the mass of a hydrogen atom
Charge = (-1)

9. Protons
Symbol: +p
Mass = 1 amu
Charge = (+1)

10. Thomson’s Model
Put both the electron and proton together and proposed the “Plum Pudding” model of the atom.

11. Neutrons
Symbol: n0
Mass = 1 amu
No charge

12. Nucleus Discovered by Ernest Rutherford.
Using the “Gold Foil” experiment, Rutherford determined:
An atom is mostly empty space.
There is a nucleus in the middle of the atom containing the protons.
The electrons orbit a large distance away from the nucleus.
Proposed the nuclear model of the atom.

13. Let’s Review

14. Atomic Number
Designates the number of protons in a nucleus of an atom.
Each element has a characteristic atomic number.
The number of electrons equals the atomic number in a neutral atom.

15. Practice (Lab Notebook)
How many protons do each of the following elements have? C Ne K

16. Mass Number
Designates the total number of protons and neutrons in an atom.
Number of neutrons = mass number - atomic number.
Atoms of the same element can have different mass numbers.

17. Practice (Lab Notebook)
How many neutrons do each of the following elements have?
C (Mass number 12)
Ne (Mass number 22)
K (Mass number 40)

18. Objective 2
Explain why isotopes differ.

19. Isotopes
Atoms with the same number of protons, but different numbers of neutrons.
Isotopes of an element have the same atomic number, but different mass numbers.

20. Describing Isotopes Nuclear Symbol or isotopic
symbol – shows number of
protons, neutrons and electrons in
an atom.
Isotopes may also be described by labeling the name following by the mass number (Example: carbon-12).

21. Practice Diagram the nuclear symbols for Lithium – 7 Helium – 4
Titanium – 48

22. Average Atomic Mass
Weighted average mass of the atoms in naturally occurring sample of an element.
On periodic table.
Ex: For Xenon-124, Xenon-126
& Xenon- 134

23. Atomic Mass Example
In nature carbon is composed of 98.89% 12C atoms and 1.11% 13C atoms. 12C has a mass of 12 amu and 13C has a mass of amu. What is the average atomic mass of carbon?

24. Objective 3
Diagram the Bohr Model of the atom.

25. Bohr Model
Niels Bohr (1913) – Created the Bohr Model stating electrons travel around nucleus in energy levels.
Uses rings to show the energy levels.
The number of rings should match the row the element is in on the periodic table.

26. Bohr Model Diagram The protons in the nucleus = the atomic number.
The neutrons in the nucleus = mass number -atomic number.
Electrons = number of protons. Fill the shells from low to high until the correct number of electrons are added.
This model works for the first 20 elements.

27. Diagram Lithium-7

28. Diagram Nitrogen-14

29. Diagram Aluminum-27

30. Diagram Calcium-40

31. Valence Electrons Electrons in the outermost energy level.
Ex: Li = 1, F = 7
Corresponds with the group number for Groups 1-2,

32. Lewis Dot Structures Show valence electrons.
Look at the group number. This is how many dots you draw for each atom.
Ex:
Potassium Fluorine Sulfur Xenon
Phosporous Silicon Aluminum Beryllium