1. Unit 02
Atomic Structure

2. Just How Small is an Atom?
You don’t need to write.
A speck 0.1 mm in diameter (about half the size of a period at the end of the sentence) requires one million atoms.
It would require a million atoms, edge to edge, to match the thickness of a page of paper.

3. Can you see an atom?
Technically, you cannot "see" anything smaller than the shortest wavelength of light that you can see it with.
But there are ways to "visualize" it, like Atomic Force Microscopy. But these are all just measurements converted to computer images, and are not in any real sense "seeing" the atom.
You can't see atoms in any normal sense of using an optical microscope.
You don't get an optical image, but it does allow you to map out an image of the atoms of a molecule. To do this you use a metallic tip which interacts with the atoms you want to image. As you move the tip over the atoms, you pass a current, called a tunneling current, between the tip and the atom. This current is extremely sensitive to the distance between the atom and the tip.

4. - REMEMBER FROM: Elements, Mixtures, and Compounds -
- a pure substance made up of one type of atom.
- organized on periodic table
- each element has a unique
number of protons…its atomic number

5. Atomic Structure: Atoms contain three subatomic particles… 1. Protons…
2. Neutrons…
3. Electrons…
positive charge
These are located in NUCLEUS!
neutral charge
negative charge
Electrons surround the nucleus in orbitals

6. Atomic Structure
An atom is considered electrically neutral. Electrically neutral means the number of protons (+) = the number of electrons (-)
4 red protons = 4 blue electrons

7. Properties of Subatomic Particles
Symbol
Relative electrical charge
Relative mass
Actual mass (g)
Electron e- 1-
1/1840
9.11 × 10-28
Proton p+ 1+ 1
1.67 × 10-24
Neutron n0
Protons and Neutrons have the same mass.

8. A. Discovery of the Atom
Ernest Rutherford discovered the nucleus by shooting alpha particles (have a positive charge) at a very thin piece of gold foil.
He predicted that the particles would go right through the foil at some small angle.

9. Rutherford’s Gold Foil Experiment

10. Rutherford’s Gold Foil Experiment
some particles (1/8000) bounced back from the foil
this meant there must be a “powerful force” in the foil to hit particle back
Predicted Results Actual Results

11. Discovery of the Atom
Purpose: The students will find the shape of different items and relate this to the early scientist that made discoveries about the shape and size of the atom. Procedure: 1. Title the left side of your spiral Discovery of the Atom. 2. For each item you will write the letters then draw your predicted shape of the item. 3. Then you will write 1 sentence describing why they think your prediction is the shape of the item. A: Item in brown bag – Use your hands to feel the shape of the item. B: Item in clay – Using the toothpicks provided find the shape of the object enclosed in the modeling clay. C: Black box – Maneuver the black box with a marble inside to discover the shape of the object enclosed.

12. B. Models of the Atom

13. J.J. Thomson
“Plum pudding” atom negatively charged e- stuck into a lump of positively charged material
– similar to chocolate chip cookies

14. Ernest Rutherford
In Rutherford’s gold foil experiment he discovered electrons surround a dense positive nucleus
“The Blow Pop”

15. Bohr Model electrons are arranged in fixed orbits around the nucleus.
ex. Orbits gum

16. Quantum Mechanical Model
Quantum mechanics was developed by Erwin Schrodinger
Estimates the probability of finding an e- in a certain position
Electrons are found in an “electron cloud”

17. I. Nuclear Symbols B 11 5

18. mass # = protons + neutrons
A. Mass Number
mass # = protons + neutrons
always a whole number
NOT on the Periodic Table!
© Addison-Wesley Publishing Company, Inc.

19. B. Isotopes Mass # Atomic #
Atoms of the same element with different mass numbers. (different number of neutrons)
Nuclear symbol:
Mass #
Atomic #
Hyphen notation: carbon-12

20. B. Isotopes

21. You must know how to find:
C. Nuclear Symbols
You must know how to find:
# of protons = atomic number
mass # = # of n0 + # of p+ (atomic #)
What’s in the nucleus of the atom
# of electrons = # of protons (in a neutral atom)
Boron 5 B
10.811
atomic number
(Not the same as the mass #)
(average) atomic mass

22. How to write a Nuclear Symbol
Charge if ion
Element Symbol B
Mass Number
= p+ + n0 -3 11 5
Atomic Number
= p+

23. C. Nuclear Symbols Chlorine-37 atomic #: mass #: # of protons:
# of electrons:
# of neutrons: 17 37 20

24. Cl Mg Nuclear Symbol Examples 35 17 27 12 17 35 17 17 18 12 27 12 12
Number of Protons
Number of Electrons
Number of Neutrons
Atomic Number
Mass Number 17 35 17 17 18 Mg 27 12
Number of Protons
Number of Electrons
Number of Neutrons
Atomic Number
Mass Number 12 27 12 12 15

25. D. Relative Atomic Mass 12C atom = 1.992 × 10-23 g
atomic mass unit (amu)
1 amu = 1/12 the mass of a 12C atom
© Addison-Wesley Publishing Company, Inc.
1 p = amu 1 n = amu 1 e- = amu

26. E. Average Atomic Mass
weighted average of all naturally occuring isotopes
on the Periodic Table
round to 2 decimal places
Avg.
Atomic
Mass

27. E. Average Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Avg.
Atomic
Mass
16.00
amu

28. E. Average Atomic Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Avg.
Atomic
Mass
35.40 amu

29. Example:
A sample of cesium is 75% 133Cs, 20% 132Cs and 5% 134Cs. What is the average atomic mass?
Answer:
.75 x 133 = 99.75
.20 x 132 = 26.4
.05 x 134 = 6.7
= average atomic mass

30. II. The Periodic Table
Periodic Law – properties of elements can be predicted by their position on the periodic table

31. A. History of the Periodic Table
Dmitri Mendeleev (1871)
Developed the first periodic table
It was arranged by atomic mass because atomic number had not been discovered
He was able to predict properties of elements 31

32. A. History of the Periodic Table
Henry Moseley (1913)
- developed the modern periodic table
- arranged in order of increasing atomic number 32

33. B. Organization of the Periodic Table
horizontal rows numbered 1 - 7
Energies of outermost electrons are similar 33

34. B. Organization of the Periodic Table
Groups/ Families
vertical columns
have similar chemical & physical properties 34

35. Group 1 (IA) – Alkali Metals35

36. Group 2 (IIA) – Alkaline Earth Metals36

37. Group 18 (VIIIA) – Noble Gases37

38. Group 17 (VIIA) - Halogens38

39. B. Organization of the Periodic Table
Metals-
Nonmetals-
Metalloids-
Left of stair step
Right of stair step
On the stair step
NONMETALS
METALLOIDS
METALS

40. REPRESENTATIVE “Group A”
B. Organization of the Periodic Table
Group A- Representative
Group B - Transition
REPRESENTATIVE “Group A”
TRANSITION “Group B”
INNER TRANSITION

41. The Extended Periodic Table41