1. Chapter 3 & Chapter 19 The Structure of the Atom & Nuclear Chemistry
Unit 2
Chapter 3 & Chapter 19
The Structure of the Atom & Nuclear Chemistry

2. Early Theories of Matter
Democritus ( B.C.) proposed & believed that
Matter was not infinitely divisible
Made up of tiny particles called atomos
Atoms could not be created, destroyed, or further divided
- This sounds like the beginning of…..

3. John Dalton
19th century
Dalton revised Democritus's ideas based upon the results of scientific research he conducted
Dalton’s atomic theory

4. Dalton’s Atomic Theory
Elements are made of extremely small particles called atoms
All atoms of a given element are identical
Same size, mass and chemical properties
Atoms are indivisible in chemical processes.
They can neither be created nor destroyed in a chemical reaction
A chemical reaction simply changes the way the atom is grouped together
A compound has a constant composition of its elements
Different atoms combine in simple whole number ratios to form compounds

5. Dalton’s Atomic Theory
Dalton’s theory was supported by 2 Laws:
The Law of Conservation of Matter (Lavoisier)
The Law of Definite or Constant Composition (Proust)
Not all of his theory is correct!!

6. What is an atom?
An atom is the smallest particle of an element that retains the properties of the element

7. The Nuclear Atom Ernest Rutherford developed a model of the atom.
His model consisted of the following ideas:
An atom consists mostly of empty space through which electrons move
Electrons are held within the atom by their attraction to the positively charged nucleus
Tiny, dense region called the nucleus, which is located in the center of the atom
Nucleus contains all of an atom’s positive charge and virtually all of its mass

9. Three Subatomic Particles
Electron
Proton
Neutron

10. Subatomic Particles in the Nucleus
Positively charged particles called protons
Proton’s charge: equal to but opposite that of an electron
Why don’t the protons repel each other in the nucleus?
Neutral particles called neutrons
Neutron mass nearly equal to that of proton
Neutron has no charge

11. Outside the nucleus Negatively charged particles are called electrons
move through empty space in atom
Negatively charged

12. Atomic Number The number of Protons in the nucleus Examples:
Carbon (C) has 6 protons
Atomic number is 6
Copper has 29 protons
Atomic number is 29

13. Atomic Number
In uncharged atom, atomic number is also the number of electrons
Why?
If an atom is charged, then it is an ion
Uncharged atom:
Atomic number = # of protons = # of electrons
Take out your periodic table

14. Mass Number To find the Mass number # protons + # neutrons
To find # neutrons
mass number – proton (or atomic number)
Mass numbers are always WHOLE #’s!!

15. Symbols for Atoms X= symbol of element A= mass number
Z= number of protons
X or X A Z A

16. Isotopes and Mass Number
C C
carbon carbon-13
Isotopes are atoms with the same number of protons but different number of neutrons 12 6 13 6

17. Isotopes and Mass Number
Example:
3 types of Potassium
All 3 types contain 19 protons and __ electrons
# of Protons # of Neutrons Mass Number

18. The End! February 2nd - Monday
Be sure to do your homework tonight!!
First daily warm-up tomorrow!!

19. What’s the difference between mass number and average atomic mass?
carbon-12
But if you look on the periodic table, the number states 12.01… 12 6

20. Mass of Individual Atoms
Mass of protons and neutrons:
1.67 x g
Mass of electron is 1840 times smaller than that of protons and neutrons
9.11 x g

21. Atomic Mass Unit (amu)
Small mass #’s are not easy to work with, so the atomic mass unit (amu) was developed
One atomic mass unit (amu) is equal to 1/12 the mass of a carbon-12 atom
The mass of 1 amu is nearly equal to the mass of one proton or neutron

22. Mass of Individual Atoms
Atomic mass:
The weighted average mass of the isotopes of an element
Example: Chlorine
Mixture of 75% chlorine-35 and 25% chlorine-37
Atomic mass = (0.75)*35 + (0.25)*37 = 35.5 amu

23. What’s the difference between mass number and average atomic mass?
Mass number- specifically about one isotope
Average atomic mass- includes the masses of all the different isotopes for that atom

24. The End! February 3rd - Tuesday
Go over test!
Warm up practice
Start handout #2

25. February 4th - Wednesday
You must complete the pre-lab questions before you can start on the labs!!
Be sure to do your homework tonight!

26. Nuclear Reactions Chemical reactions
What can NOT change in a chemical reaction?
Nuclear Reactions: changes that occur in the nucleus of an atom
The nucleus is unstable!!
Most atoms have unstable nuclei.

27. Why are some stable, while others are not?
Primary Reason:
ratio of the neutrons to the protons (n/p)
An atom is most stable when the ratio is 1:1
The maximum ratio of stability is around 1.5 : 1

28. Radioactivity
An unstable nucleus emits rays and particles, called radiation, to become stable
The process is called radioactivity
Gain stability by LOSING energy

29. Radiation
Three types of radiation produced:
Alpha
Beta
Gamma

30. 3 Radioactive Particles
1. Alpha Particle (+)
It travels about 1/10 the speed of light (slowest)
It is the largest, most massive particle
It is the most dangerous if ingested
It has the least penetrating ability - paper can stop this particle

31. 3 Radioactive Particles
2. Beta Particle (-)
Fast accelerated electron
Ejected when a neutron is converted to a proton in the nucleus
Travels 1/4 the speed of light.
It is lighter and faster than the alpha particle.
Average penetrating ability - can be stopped by heavy clothing

32. 3 Radioactive Particles
3. Gamma Ray
Not really a particle; it is a form of energy from the electromagnetic spectrum (EM)
Has no mass and no charge.
Always accompanies either beta or alpha radiation.
Very high powered
Travels at the speed of light.
Highest penetrating ability - can be stopped by heavy shielding such as lead.

33. Alpha Decay An alpha particle is released
A new atom is formed in the product in which:
a) the atomic number is lowered by 2
the mass number is lowered by 4
Example:

34. Beta Decay
A neutron is converted in the nucleus of an atom resulting in:
a) beta particle released
b) a new atom in the product whose atomic number increases by 1
c) mass number does not change
Example:

35. The Law of Conservation of Matter must be observed!!
Gamma Radiation
It is the “Energy” of the reaction
Always accompanies alpha and beta emissions.
Regardless of radiation or decay,
The Law of Conservation of Matter must be observed!!
The nuclear equation must be BALANCED!!

36. RADIOACTIVE PARTICLES Summary

37. Half Life
The half life of a radioisotope is the time it takes for half of the sample to decay.
Half-life is represented by “t1/2”
The number of half-lives that have passed is represented by “n”

38. Amount Remaining
You can use two equations, depending on what information you have
If you have the # of half-lives that have passed..
initial amount x (1/2) n
n= # of half-lives that have passed
If you DON”T have the # of half-lives that have passed..
initial amount x (1/2) P/ t1/2
p= time that has passed
t1/2= time of half-live

39. Half-life problem
If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours?
What percent of it is remaining?

40. Handout #5 Equations to Add
To find the half-life
t1/2= time passed/ # of half-lives passed
To find the # of half lives that have passed…
n= time passed/ one half-life
Total time passed= n times t1/2

41. Problem 3 Given information I= 64g r= 2.0g p=12.5 hours n=?
One half-life=??

42. FUSION and FISSION Fission is the splitting of nuclei
resulting in a tremendous release of energy
heavy atoms split so they can become more stable
Fusion is the combining of nuclei
resulting in more energy being released than fission
The sun produces energy as a result of nuclear fusion
2 H atoms combine to form Helium

43. The End! February 6th - Friday
Finish Review sheet this weekend!
Review on Monday!
Change of Schedule:
Do half-live lab on Monday!