1. Atomic Structure and Timeline
Objectives:
Describe the process why which the atomic structure was discovered
Describe what an atom is an what makes it up.
Identify differences in protons, neutrons and electrons

2. Democritus
400 BC
Proposed that matter was composed of tiny indivisible particles
Not based on experimental data

3. John Dalton
1807
British schoolteacher that based his theory on other’s data
Billiard Ball Model
Atom is uniform, solid sphere

4. Dalton’s 4 Postulates
Elements are composed of small indivisible particles called atoms
Atoms of the same element are identical. Atoms of different elements are different.
Atoms of different elements combine together in simple proportions to create a compound.
In a chemical reaction, atoms are rearranged, but not changed

5. Henri Becquerel 1896 Discovered radioactivity
Spontaneous emission of radiation from the nucleus
Alpha, beta and gamma (p, neg, neu)

6. J.J. Thomson Cathode Ray Tube Experiments Discovered electrons
Beam of negative particles
Discovered electrons
Negative particles within an atom
Plum-pudding Model

7. Plum-Pudding Model

8. Ernest Rutherford 1911 Gold Foil Experiment Discovered the nucleus
Dense, positive charge in center of atom
Nuclear Model

9. Niels Bohr 1913 Energy Levels
Electrons can only exist in specific energy states

10. Erwin Schrodinger 1926 Quantum mechanics Electron Cloud Model
E- can only exist in specified energy states
Electron Cloud Model
Orbital-region around nucleus were electrons are likely to be found

11. James Chadwick 1932 Discovered neutrons
Neutral particles in the nucleus of an atom

12. Atomic Structure An element is composed of one type of atom
Atom—smallest piece of matter that sill retains the properties of the element
Composed of: protons, neutrons and electrons

13. Atomic Components Protons (+1)and neutrons (neutral) found in nucleus
Nucleus--Positively charged
Surrounded by electrons(-1)
Nucleus—center core of atom

14. Most of the atom’s mass.
Atomic Number
equals the # of...

15. Atomic Components
Protons and neutrons are made up of quarks So far, only 6 uniquely different quarks Scientist theorize that 3 quarks held together with strong nuclear force produces a proton A different arrangement of 3 other quarks produces a neutron

16. Electron Cloud Model
Electron cloud—area around the nucleus of an atom where electrons are most likely found
100,000 times larger than the diameter of the nucleus
Electrons in the cloud are a lot smaller than a proton
Electrons are so small and moves so quickly, it is impossible to describe its exact location
Bohr Model:
Electrons can only exist at certain energy levels
Low levels—close to nucleus
Each level can hold 2n2
Level 1—2
Level 2—8
Level 3—18
Level 4--32

17. Atomic Mass
Nucleus contains most of the mass b/c protons and neutrons are so large
Mass of proton and neutron are about equal

18. Atomic Mass Unit of measurement—atomic mass unit (amu)
Mass of a proton and neutron is about 1 amu

19. Protons The number of protons defines the atom
Ex. Every carbon atom has six protons; all atoms with six protons are carbon atoms
# protons=atomic number

20. Mass Number Sum of protons and neutrons in the nucleus of an atom
Always a whole number

21. Neutrons Number of neutrons=mass number-atomic number
Not all atoms of an element have the same number of neutrons
Isotopes—atoms of same element with different number o f neutrons
Mass Number
Atomic Number

22. Isotopes

23. Identifying Isotopes
Models of two isotopes of boron are shown below. Neutrons are different, so the mass numbers are different
You use the name of the element followed by the mass number of the isotope to identify each
Boron-10 and boron-11

24. Identifying Isotopes
Average atomic mass—weighted-average mass of the mixture of isotopes
4 out of 5 atoms of boron are boron-11 and one out of five are boron-10

25. Practice
Using the periodic table of elements in the back of your text book:
Identify the number of protons, neutrons and electrons in each of the following elements
Ca, B, C, O, N, F, Na, K, Mg, Mn, Si, As, He, H
Draw an Electron Cloud Model (Bohr Model) for each of the following elements
Cl, Br, N, O, C, Mg

26. Project Pick an element on the Periodic Table
Construct a 3D Bohr Model of that element
Make a brochure using the same element
Include:
Atomic mass
Atomic number
Who discovered it
When was it discovered
How was it named
What is its natural state
Melting/boiling point
Group
Characteristics
Interesting facts
Pictures
Bohr model
Due Friday