1. Atomic Structure, The Periodic Table & Atomic Theory
What’s it all about?

2. The Basic Atom
Smallest particle of an element that still has the element’s properties
Atomic Theory explains what atoms look like, and how and why they behave the way they do
Democritus (400 BC) proposed the existence of atoms (philosophy)
John Dalton (1800) was the first to have scientific evidence to support this
Considered the Father of Modern Atomic Theory

3. Dalton’s Atomic Theory
Dalton’s experiments showed him several things about the existence of atoms – he had 5 postulates
All matter is made of atoms
Atoms are small, indestructible spheres
Atoms of the same element are identical
Atoms always combine in compounds in whole number ratios
In chemical reactions atoms are combined, separated or rearranged

4. Dalton’s Model The Marble Model
Dalton’s idea of the atom was a small sphere hence

5. Current model “building blocks of matter”
Charge: Neutral (no charge) particles
made up of 3 subatomic particles in 2 regions
Nucleus
Tiny
Positively charged
Dense mass in the atom’s center
has 2 particles
(p+) protons
each has a (+1) charge
has a mass of 1 a.m.u.*
(n) Neutrons
no charge
*a.m.u. = atomic mass unit
Electron Cloud:
Diffuse (spread out very thinly)
Negatively charged
area outside of the nucleus
Electrons (e-):
each has a (-1) charge
little mass (0 amu)
located outside of the nucleus

6. Region & Particle Relationship
Atoms
Nucleus
Electron Cloud
Region
Subatomic Particle
Neutron
Proton
electron + -
Charge
Charge Balance

7. Atomic Particles
The Electron

8. The Electron– Fun Facts
Abbreviated e-
Gives the electron cloud its charge
Gives the element its chemical properties
Structure: Lepton (fundamental particle not made of smaller particles)
Mass = 0 amu* (amu = atomic mass unit)
Not really 0 but 1/1200-1/2000th the mass of a proton)
Charge: negative (exactly balances the p+ positive charge)
Location: Electron Cloud

9. The Electron on the Periodic Table
How many electrons are there in an element?? Where do you find it??? 20 Ca
Calcium
40.078
# of e- = Atomic Number but only in a neutral atom
Let’s make a note on our PT & test each other

10. The Electron – History/Theory
Discovery #: 1st subatomic particle discovered
Discovered by JJ Thomson in 1897
JJ Made a CRT (cathode ray tube) and found that when he shot electricity through it a beam of light appeared
The beam of light was affected by magnetic & electric forces (does light do that??)
He proposed that it wasn’t light but tiny, negatively charged particles he called electrons (btw: he thought the discovery was useless)

11. Thomson’s Model The atom was Neutral in charge so…
Most of the atom was a diffuse positively charged “goo” or matrix
Electrons were tiny particles that floated around in the “goo”.
Electrons were very tiny compared to the mass of the atom

12. The Thomson Plum Pudding Model
1897 – The Plum Pudding Model
I prefer the “Chocolate Chip Cookie Dough Model
negative electrons
positive matrix or goo that made
up the rest of the atom

13. Atomic Particles
The Proton

14. The Proton – Fun Facts Abbreviated p+
Gives the nucleus a positive charge
Gives the element its unique characteristics & identifies the element (# p + is unique to each element
Structure: Hadron (composite particle made of smaller particles)
Mass = 1 amu*
Charge: Positive
Location: Nucleus

15. The Proton on the Periodic Table
How many protons are there in an element?? Where do you find it??? 20 Ca
Calcium
40.078
# of p+ = Atomic Number
Let’s make a note on our PT & test each other

16. The Proton – History/Theory
Discovery #: 2nd subatomic particle discovered
Discovered by Ernest Rutherford in 1918
Rutherford first proposed the positive nucleus in 1911 from the “Gold Foil Experiment” changing the model of the atom again

17. Rutherford’s Models The nucleus was
Very dense
Had most of the mass of the atom
Was positive
Very, very tiny compared to the entire atom
Atoms are mostly empty space
The electrons move around the outside of the nucleus
Rutherford model – nuclear model – kind of like a plasma ball w/ a tiny positive nucleus and electrons floating around outside it
Discovered the proton later in the first nuclear reaction
How tiny? 400 x tinier than this – and that’s only the nucleus!!! Protons are smaller yet!!!!

18. The Rutherford (Nuclear) Models
1911 Model with just a positive nucleus
in the center of the electrons
1918 Model with protons making
up the nucleus

19. Atomic Particles
The Neutron

20. The Neutron – Fun Facts Abbreviated n0 Adds mass to the nucleus
Helps hold the nucleus together (prevents proton repulsion from destroying the nucleus)
Structure: Hadron (composite particle made of smaller particles)
Mass = 1 amu*
Charge: Neutral (no charge)
Location: Nucleus

21. The Neutron on the Periodic Table
How many neutrons are there in an element?? Where do you find it??? 20 Ca
Calcium
40.078
#n0 is NOT found on the PT
More on this later

22. The Neutron – History/Theory
Discovery #: 3rd subatomic particle discovered
Discovered by James Chadwick (also a student of JJ Thomson) in 1936 – (Rutherford said it should be there, Chadwick gave them evidence)
Chadwick produced a beam of neutral particles that knocked protons out of paraffin wax
Led to the development of the atomic bomb

23. Chadwick’s Model
Similar to the current model with p+ & n0 in the nucleus and e- orbiting the nucleus in the electron cloud

24. Atomic Particles
Isotopes & The Neutron

25. Isotopes & the Neutron
Isotopes: Atoms of the same element with different numbers of neutrons
The number of neutrons can be different in an element (that’s why there is no neutron number on the PT)
The number of neutrons must be calculated for each isotope
Example: Magnesium has 3 isotopes
Symbol #p+ #n0 #e-
Mg - 24 12 12 12
Mg - 25 13
Mg - 26 14

26. Isotopes & Mass Number
Mass number (mass #) is the number of p+ & no in a specific isotope of an element
Mass # = #p+ + no
or #no = Mass # - #p+
Lets put this on the PT somewhere

27. Isotopes & Mass Number #1
How do you know which isotope you have??
Mass # is found in one of 2 ways – prioritized list
Isotope Notation
(given to you with the element symbol) – 100% accurate
Mass #
Element Symbol
C-14
Mass # OR 14 6 C
Element Symbol
Atomic #
So in C-14 there are…
6 p+ & 6 e- (atomic number of C is 6)
8n0 (Mass # - # p+ = #n0 or = 8 )

28. Practice Isotope Notation
Isotope Symbol
# p+ #n0 #e-
O-18
N-15
Si-30
Cl-37
K-41
Fe-54
Ni-62
Cu-65
Br-79
8 10 8
7 8 7

29. Isotopes & Mass Number #2
How do you know which isotope you have??
2. MCI (most common isotope) –50% accuracy
Round the Average Mass to a whole number to get mass # for the m.c.i.
Average mass = amu so…. round it and …
The mass number of the most common isotope is 40 so Ca-40 20 Ca
Calcium
40.078 5 B
Boron
10.806
Average mass = amu so…. round it and …
The mass number of the most common isotope is 11 so B-11

30. Average Mass

31. Practice M.C.I. method Isotope Symbol # p+ #n0 #e- O N Si Cl K Fe NiCu Br
16 (avg mass = )
8 8 8
14 (avg mass = )
7 7 7
28 (avg mass = )
35 (avg mass = )
39 (avg mass = )
56 (avg mass = )
59 (avg mass = )
64 (avg mass = )
80 (avg mass = )

32. Sample Formats Carbon - 12 Carbon - 13 Carbon - 14 Isotope Name6 6 6 6 7 8
Isotope Name
Isotope
Symbol
# p+
# n
# e-
Lithium – 6
Li – 6
Lithium – 7
Li – 7
Iron –
Fe – 28
Fe- 31
Chlorine
Mercury 3 3 3 3 4 3 54 26 26 57 26 26
Cl - 35 17 18 17
Hg - 200 80
120 80

33. Atomic Particles
The Electron Cloud

34. Atomic Structure – electron cloud
Nucleus
1st Energy Level:
holds up to 2 e-
The region of the atom around the nucleus where the electrons are located
Makes up most of the atom’s size
Mostly empty space
Made up of energy levels that e- can move in and out of by absorbing & releasing energy
e- absorb energy and move to higher levels or release energy and drop back to lower levels
2nd Energy Level:
holds up to 8 e-
3rd Energy Level:
holds up to 18 e-
4th Energy Level:
holds up to 32 e-
Formula: ??
Skip valence e- for now

35. Atomic Theory – Electron Cloud
Energy levels were proposed by Neils Bohr in 1913
His data supported that e- absorb heat/electrical energy & then release the energy as certain colors of light
He concluded that e- orbited the nucleus in energy levels
Jumped to higher levels when absorbing energy
Released light energy when they fell back down

36. Atomic Model– Bohr Model
Neils Bohr’s model is sometimes called the planetary model but we usually call it the…
Bohr Model
light
released
e.l. = 3
e.l. = 2
e.l. = 1
Time for a demo

37. Electron Cloud – Later Discoveries
In 1926 Erwin Schrodinger & Max Born proposed that electrons actually behaved more like waves than particles and therefore proposed the wave model. Schrodinger is famous for his “Schrodinger’s Cat” example used to explain this model
The quantum mechanical model of the electron cloud is our current model and many scientists have contributed to its development.
discovered e- exist within orbitals, which are not circular, within the energy levels
dark, shaded areas of the cloud are more likely to contain e-