1. Unit 2: Atomic Structure

2. I. The Evolution of Atomic Theories
Around 400 BC
A. Democritus (Year _______________)
First to suggest the existence of fundamental particles – called them atoms
Believed they were indivisible and indestructible
Smallest particle of matter

3. 1803-1805 B. John Dalton (Year __________)
Dalton studied the ratios in which elements combine in chemical reactions. Based on his experiments, he formulated the first theories about atoms.
Dalton’s Atomic Theory:
1. All matter is composed of ATOMS
2. All elements are composed of INDIVISIBLE ATOMS (SOLID/HARD SPHERE)
3. All atoms of a given element are IDENTICAL (SAME MASS AND PROPERTIES). Atoms of different elements have DIFFERENT MASSES/PROPERTIES

4. (Ex – Fe2O3 vs. FeO or H2O vs. H2O2)
Dalton’s Atomic Theory (Continued):
Law of Definite Proportions: Atoms can combine with each other in simple-whole number ratios to form compounds
(Ex – H20, AgNO3)
Law of Multiple Proportions: Atoms can combine in 2 or more ways to form compounds
(Ex – Fe2O3 vs. FeO or H2O vs. H2O2)

5. 1906 C. JJ Thomson (Year ________)
Discovered the electron (e-) using a cathode ray tube
Rays were deflected when a magnet was brought near
He concluded that: these beams were negatively charged particles and were part of EVERY ELEMENT
VIDEO CLIP
VIDEO CLIP

6. C. JJ Thomson (CONTINUED)
He called these particles ELECTRONS (e-)
Thomson Atomic Model: “Plum Pudding Model”
Electrons and positive charges were dispersed throughout the atom

7. 1911
D. Ernest Rutherford ( )
Directed alpha particles (42 He) at a thin piece of gold foil
If the Thomson model was correct, atoms would pass through undisturbed. However… some were slightly deflected
VIDEO CLIP

8. D. Ernest Rutherford (Continued)
Based on the deflection of alpha particles, he concluded that:
1. Atoms are made up of mostly empty space
2. Positively charged nucleus and electrons orbit around it
Rutherford Atomic Model: _______________
Atomic Nucleus

9. E. Neils Bohr (_______) 1913 Expanded the atomic model
He proposed that:
Electrons orbit the nucleus in specific PRINCIPLE ENERGY LEVELS (PELs)
His atomic model:
Planetary Model
1st PEL
2nd PEL
Video Clip

10. E. Neils Bohr (Continued)
In his model, electrons could move between different energy levels by absorbing or releasing energy
Excited State: Electrons can absorb energy (typically in the form of heat) and if they absorb the right amount, they move to a higher PEL
Bohr Model Animation
Absorb Energy

11. E. Neils Bohr (Continued)
Ground State: Electrons become unstable in the excited state and fall back down to lowest available energy level (ground state)
Bohr Model Animation
Energy Released

12. E. Neils Bohr (Continued)
Electrons want to be in the ground (stable) state
Photon Release: when the electron returns to ground state it releases the energy it absorbed in the form of a PHOTON (light energy) to become stable
This can be seen in
Fireworks
Energy (Photon) Released

13. 2n2 E. Neils Bohr (Continued)
Principle Energy Levels: Each PEL can hold only a certain amount of electrons
2n2
n = 1 2
n = 2 8
n = 3 18
n = 4 32
Electrons in higher energy levels have more energy

14. F. Erwin Schrodinger(_______)
1926
He proposed that:
Electrons do not travel around in circles around the nucleus, instead, randomly move in regions (orbitals)
Orbital:
A region in which an electron is most likely be located

15. E. Erwin Schrodinger(_______)
1926
His atomic model:
Wave-Mechanical Model

16. Particles in nucleus are called NUCLEONS
II. Atomic Structure p
+ 1
1 amu
nucleus n
1 amu
nucleus e-
- 1
0 amu
PEL
Particles in nucleus are called NUCLEONS
Atomic Mass Unit (AMU)
1 AMU = 1/12 the mass of Carbon-12 atom (approx x kg)

17. II. Atomic Structure Atomic Number: Number of protons in an atom
Atomic # identifies the type of element it is
Atomic #
Example: Iron - ________ - _______
26 (26 protons)
Nuclear Charge:
Depends on the number of protons
Atomic Charge:
The total charge of an atom is is ALWAYS neutral
(# of protons equals # of electrons)

18. II. Atomic Structure 27 e- Example: Cobalt (Co) - ________ and _______
Mass Number:
# of protons + # of neutrons
Isotopic Notation:
Shows the mass of an atom along with element symbol

19. II. Atomic Structure Mass # 4
Example: 94 Be ______ p; _______ n; _______ e- 5 4
Atomic # 6
Example: C – ____ p: ____ n; ____ e 8 6
Mass #

20. II. Atomic Structure (pg 5 continued)
Drawing Atom with Principle Energy Levels: . .
C - 14 .
Valence e- : .
e- in the outer energy level (IMPORTANT) .
6 p
8 n .
Kernel e- :
Everything but valence e-
PEL 1
PEL 2

21. SKIPPING TO SECTION IV

22. IV. Isotopes (page 6 in notes)
Atoms of the same element, BUT different number of neutrons and different mass 1 1
11H 1 1 2
21H 3 1 2
31H

23. IV. Isotopes (page 6 in notes)
Example: Find the number of neutrons in an atom of Se-79
Atomic # = 34
Mass # = 79
7934 Se
# of n = Mass # - Atomic #
= 79 – 34 = 45 n

24. IV. Isotopes (page 6 in notes)
Example: Find the number of neutrons in an atom of Cr
Atomic # = 24
Mass # = 52
# of n = Mass # - Atomic #
= 52 – 24 = 28

25. V. Atomic Masses (page 6 in notes)
The mass found on your period table is NOT the mass of a single atom of that element. That number is the atomic mass which is the average of the isotopes and their abundance for that element. (ex. – C’s atomic mass is )
Atomic Mass:
the average mass of the naturally occurring isotopes based on each of the isotopes’ abundance and mass number

26. V. Atomic Masses
How to find the atomic mass: Carbon has two naturally occurring stable isotopes . Most carbon atoms % are C-12, while the remaining 1.108% are C-13. What is the atomic mass of carbon?
(Count sig. figs. ONLY for percents! Then add and round to the place with least number of sig. figs)
Step 1: Convert % to decimal # and multiply the decimal by its mass number
(0.9889)
(12 amu)
= amu
( )
(13 amu)
= amu
Step 2: Add the masses of isotopes
12.01 amu
11.87 amu amu =

27. V. Atomic Masses
92.21% of Si is found to be amu, 4.70% is found to be amu, and the remaining 3.09% is found to be Calculated the atomic mass of carbon
27.98 amu (0.9221) = amu
28.98 amu (0.0470) = 1.36 amu
29.97 amu (0.0309) = amu
25.80 amu amu amu = amu

28. VI. Ions
An atom that has lost or gained electrons (# of protons does NOT EQUAL # of electrons)
Example: 2311 Na +1
# of p =
# of n =
# of e- = 11
Mass # =
Atomic # =
Ion Charge = 23
23 – 11 = 12 11
Atomic # - Ion
Charge +1
# of e- = 11- (+1) = 10

29. VI. Ions Anion: Negatively charged ion (atom GAINED e-) Cation:
Positively charged ion (atom LOST e-)
Remember:
a CATion is PAWsitive

30. VI. Ions Examples: 3 15 16 18 Mass # - Atomic # Atomic # - Charge
Lost e- (cation) 3
7 – 3 = 4
3 – (+1) = 2
7 Li ______ p ________ n ____________ e ________
31 P – 3 ______ p ________ n ________ e ___________
79 Se – 2 ______ p ________ n ________ e ___________
19 F – 1 ______ p ________ n ________ e ___________
Gained e- (anion) 15 16 18
gained e (anion)
gained e (anion)

31. MOVING BACK TO SECTION III

32. F III. Valence Electrons Involved in chemical bonding
Lewis Structure (Dot Diagrams):
Symbols that represent the # of valence e- of an element
Examples:
Valence e-
Ca N F
2-7
2-5 F N Ca

33. III. Valence Electrons Bonding Sites:
Where there is only a single electron (allow other atoms to “attach” or “lose” these single electrons)
2-4
Bonding Sites C

34. III. Valence Electrons Electron Configurations:
Shows how electrons are distributed in each atom (SEE PERIODIC TABLES)
Examples:
2-8-1 10 1
Na: ___________ = ___ kernel e- ___ valence e-
Ne: ___________ = ___ kernel e- ___ valence e-
Al: ___________ = ___ kernel e- ___ valence e-
2-8 2 8
2-8-3 10 3

35. III. Valence Electrons Excited State Electrons and Emission Spectrum:
A method used to identify unknown elements
How electrons become excited (youtube)
How spectra is produced (youtube)
Periodic Table of Emission/Absorption Spectrum

36. III. Valence Electrons Excited State Configuration:
If electrons are excited (gained energy), they can move to a higher energy level
Examples:
Excited (excited Na)
2 – 7 – 2: ______ 2 – 8 – 4 : ________
2 – 8 – 17 – 2: ______ 2 – 8 – 10 – 2: _______
Ground
(Si)
Excited
(excited Cu)
Ground
(ground Ti)

37. III. Valence Electrons Excited State Configuration:
Which electron configuration could represent a strontium atom in the excited state?
1) )
2) )
Ground State for Sr: