1. Atomic Structure

2. Stepwise Timeline of Atomic Theory
Rutherford
1911
Dalton
1803
Modern Theory
Thomson
1897
Bohr
1913
Chadwick 1932

3. Democritus ~ 460 B.C. to 360 B.C.
Who
Greek Philosopher
What
Atoms cannot be created, destroyed or divided.
How
Observing nature

4. Dalton’s Atomic Theory
Who
John Dalton ( ), an English schoolteacher and chemist
What
proposed his atomic theory of matter in 1803.
Although his theory has been modified slightly to accommodate new discoveries, Dalton’s theory was so insightful that it has remained essentially intact up to the present time.

5. Dalton What ( write this outside the text box)
Cannot be created or destroyed.
All atoms of one element are exactly alike, (same size, mass, properties) but different from atoms of other elements
Combine in whole number ratios to form compounds.
How-
work with gases

6. J.J. Thomson -1903 Who a British physicist. What Plum Pudding model
(or Chocolate Chip
Cookie model)
Discovered electrons
Model
Atom was a positively charged sphere with negative electrons in it like chips
POSITIVE CHARGE
ELECTRONS

7. J. J. Thomson
How
discovered that cathode rays are made up of invisible, negatively charged particles referred to as electrons.

8. Ernest Rutherford What Who Found nucleus (1911) British chemist
Occupies a small volume of the atom
Contains almost all the mass of the atom
Electrons orbit around nucleus
Discovered proton
Who
British chemist
and physicist.

9. Ernest Rutherford How Gold Foil Experiment
Alpha particles which are positively charged pass through unmolested most of the time.
Occasionally they would bounce off when they hit something (proton) that was also positively charged.

10. Niels Bohr - 1913 Who Danish Physicist What Planetary Model
Electrons (e-) have definite path around the nucleus (orbit)
e- arranged around the nucleus according to energy level
e- with lowest energy level are closest to nucleus
How
Spectral emission lines
Who
Danish Physicist

11. Chadwick What Discovered the neutron in 1932 How Used alpha particles
Who
British Scientist
What
Discovered the neutron in 1932
How
Used alpha particles

12. Modern Atomic Theory
1. All matter is made up of very tiny particles called atoms.
2. Atoms of the same element are chemically alike.
3. Individual atoms of an element may not all have the same mass. However, the atoms of an element have a definite average mass that is characteristic of the element.
4. Atoms of different elements have different average masses.
5. Atoms are not subdivided, created, or destroyed in chemical reactions.

13. Atom and Elements
Element - a substance that is composed of a single type of atom.
Atom - the smallest particle of an element that retains the properties of that element.
The diameter of an atom is measured in nanometers
1 nm = 1 x 10-9 m = m
Atoms are composed of sub-atomic particles.

14. Proton Discovered by Ernest Rutherford in early 1900’s
Determines the identity of an atom
Relative mass of 1 atomic mass unit
Part of the nucleus of an atom
Positive charge
If you change only the # of protons, you change the element being described.

15. Neutron Discovered by James Chadwick in 1932
Determines the isotope of an atom
Relative mass of 1 atomic mass unit
Part of the nucleus of an atom
No charge (neutral)
If you change only the # of neutrons, you have a new isotope (variety) of the element .

16. Changing the number of neutrons
Creates ISOTOPES -
Atoms of the same element but with a different number of neutrons.
Isotopes of an element have nearly identical chemical properties

17. Electron Discovered by J. J. Thomson in 1903
Determines the charge of an atom (charged atoms are called ions)
Relative mass of 0 (~1/1836) atomic mass unit
Make up the electron cloud of an atom
Negative charge

18. Changing the number of electrons
When an atom loses electrons, it results in a net positive charge and is called a CATION
ions are I itive

19. Example of a cation
Neutral potassium (K) has 19 protons and 19 electrons. 19 protons = electrons = -19 0
If potassium (K) loses an electron, it only has 18 electrons. 19 protons = electrons = This is written as K+1 and is called a cation

20. Changing the number of electrons
When an atom gains electrons, it results in a net negative charge and is called an ANION

21. Example of an anion
Neutral bromine (Br) has 35 protons and 35 electrons. 35 protons = electrons = -35 0
If bromine (Br) gains an electron, it has 36 electrons. 35 protons = electrons = This is written as Br -1 and is called an anion

22. Gained electron
Lost electron
cation
anion

23. Describing an atom Equals the number of protons in an element.
ATOMIC NUMBER
Equals the number of protons in an element.
In a neutral atom, the atomic number also equals the number of electrons.
- All atoms of the same element have the same number of protons.
The smaller of the two numbers in the periodic table square, always a
whole number

24. Describing an atom
ATOMIC MASS
A weighted average of the mass of all the isotopes (varieties) of an atom
Each element has only one atomic mass
Also called “average atomic mass”
The larger of the two numbers in the periodic table square
Always a decimal number

25. Describing an atom MASS NUMBER
Equals the # protons + # neutrons in an atom
Not always the same for atoms of an element  isotopes
Not listed on the periodic table
Always a whole number

26. APE MAN A = Atomic Number P = Number of Protons
E = Number of Electrons
M= Mass number
A = Atomic Number (again)
N = Number of Neutrons
Always the same number in a neutral atom
Mass Number minus Atomic number equals Number of neutrons

27. Isotope Notation
mass number C 12 6
element symbol
atomic number

28. Isotope Name name of the element dash mass number
Example: Carbon -14 is the isotope name for a carbon atom with a mass number of 14

29. C Isotope Notation mass number 14 element symbol 6 atomic number
number of neutrons = mass number – atomic number.
How many protons and neutrons in this isotope?

30. Practice 14 18 Isotope notation Isotope name Atomic number Mass #
# of p+
# of no
# of e-
Silicon - 14 18
Helium - 4

31. Determining (Average)Atomic Mass
To determine the atomic mass you must know what percent of each isotope of the element is found in nature. This is called the relative abundance.
Example: There are 2 common isotopes of Chlorine.
25% is chlorine - 37
75% is chlorine - 35
Calculate the average atomic mass of chlorine.

32. Average Atomic Mass Neon in nature is 90.5% Neon-20,
0.3% Neon-21, and 9.2% Neon-22.
What is the average atomic mass of Neon?

33. REACTIONS CHEMICAL NUCLEAR
involve the transfer or sharing of electrons
involve the absorption or emission of particles by the nucleus of an atom

34. Nuclear Chemistry Vocabulary
Nuclide- General name given to the nucleus of an atom
Parent nuclide- initial nucleus
Daughter nuclide- the nucleus after the decay has occurred

35. Nuclear Chemistry Vocabulary
Radiation - energy that is emitted from a source and travels through space.
Ionizing Radiation- Has enough energy to change atoms and molecules into ions; examples: X-rays and gamma rays.
Nonionizing Radiation- Does not have enough energy to ionize matter; examples: radio waves, microwaves
Accidentally discovered by Henri Becquerel in 1896 when he was performing a lab with fluorescent screens.
Radioactivity is the spontaneous emission of radiation from the nucleus of an atom.

36. Types of Ionizing Radiation
Symbol
Charge
Penetrating Ability
Size
Alpha He
or 
positive (deflected by a magnet)
Limited ability to pass through matter.
(can be stopped by paper)
Big
Beta
formed when a neutron splits e or
-1
negative
(deflected by a magnet)
Can penetrate better than alpha
(can be stopped by a few mm of Al)
Small
Gamma 
Neutral
(is not deflected by a magnet)
Penetrates the farthest.
(several cm of lead or a larger layer of concrete will block )
nothing 4 2

38. penetrating ability

40. Why decay happens To become more stable.
Large atoms are stable when the neutron: proton ratio is 1.5:1
Decay happens when the neutron: proton ratio is too high.

41. Alpha decay

42. Alpha Decay Occurs when an alpha particle leaves the nucleus
- alpha particle = Helium nucleus
Parent  daughter: mass decreases by 4 and atomic number decreases by 2
Example: Thorium-230 undergoes alpha decay. Write the decay reaction.
Th > He Ra

43. Alpha decay practice
Write the decay reaction for alpha decay of Uranium-238.

44. Beta decay
Ac +

45. Beta Decay occurs when a beta particle e is emitted from the nucleus
Parent  daughter: equal mass but atomic number increases by 1.
a neutron becomes a proton.
Example: Carbon-14 undergoes beta decay. Write the decay reaction.
C -----> e + N

46. Beta decay practice
Write the decay reaction showing beta decay of Thorium-234.

47. Fission and Fusion

48. Fission Reaction Nuclear reaction Splitting an atom’s nucleus
Releases energy
Alpha, beta are examples
Used in nuclear reactors
Causes a chain reaction
Problem: produce radioactive waste; storage of fuel is dangerous

50. chain reaction

51. Fusion Nuclear reaction
Two light nuclei are combined to form one heavier more stable nuclei
Energy is released
this is how stars are fueled
Problem with using on Earth: requires EXTREMELY high temps and high pressure

53. fusion in the sun

54. How come the protons hang out with each other?
The charge of a proton is positive. It is repelled by other protons. So, how do the protons stay in the nucleus? Shouldn’t they want to avoid each other?
The answer is that a Strong Nuclear Force exists, which is a very strong, but short range, force between quarks that keep the nucleus together by overcoming the repulsion between the protons.