7. The Nuclear Atom
In 1932, James Chadwick discovered a nuclear particle that was not affected by a charge.
The nucleus contains PROTONS and NEUTRONS.
Protons and neutrons have approximately the same mass.
Protons are POSITIVE
Neutrons are NEUTRAL

8. The Nuclear Atom
The nucleus of an atom has a diameter of 10-3 pm and electrons are 10-1 nm away from the nucleus.
The ELECTRONS in an atom are responsible for the chemical properties of the element.
The PROTONS and NEUTRONS make up the mass of an atom and are responsible for the stability of the atom.

9. The identity of an atom is determined by the number of PROTONS.
The Nuclear Atom
The identity of an atom is determined by the number of PROTONS.
Atoms of an element with different numbers of NEUTRONS are called ISOTOPES.
The number of PROTONS in an element is represented by the ATOMIC NUMBER
The numbers of NEUTRONS and PROTONS in an element are represented by the MASS NUMBER

10. The Nuclear Atom
Standard Nuclear Notation is used to represent each isotope in existence. X A Z
A = Mass Number
X = element symbol
Z = Atomic Number

11. F The Nuclear Atom 19 9 Example:
Write the symbol for the atom that has an atomic number of 9 and a mass number of 19. F 19 9
How many protons, neutrons and electrons does this atom have?
PROTONS = 9
NEUTRONS = 10
ELECTRONS = 9

12. Nucleus of an atom Nucleus
The dense, central portion of the atom
Which particles are found inside the nucleus?
Protons ( positively charged )
Neutrons ( neutral)
The particle found outside the nucleus is the electron (negatively charged)

13. Isotopes
An atom of lead will always have the same number of protons and electrons, but can have varying numbers of neutrons
These atoms are called Isotopes

14. Isotopes
Atom that has the same number of protons but different number of neutrons and mass number.
Examples of isotopes:
1 proton and 0 neutrons is hydrogen-1
1 proton and 1 neutron is hydrogen-2
1 proton and 2 neutrons is hydrogen-3

15. Atomic Theory & Nuclear Chemistry
Chapter 28

16. Reactions Chemical Nuclear
Identity of atoms can change.
Contents of the nucleus change.
Identity of atoms remains constant.
Atoms are joined, rearranged, or separated from one another.

17. Radiation
Radiation can be penetrating rays emitted by a radioactive source, but….
Not all radiation is harmful!
Heat/light are also forms of radiation.
Elements with atomic numbers greater than 83 are radioactive.

18. Nuclear Reactions FISSION – splitting a nucleus
(ex.atomic bomb, nuclear reactors)
FUSION – joining two nuclei
(ex. energy released from the sun,
hydrogen bomb).
Both types of reactions produce energy.
Both makes nucleus more stable.

19. Atoms that lie ABOVE the band of stability have TOO MANY NEUTRONS.
Atoms that lie either above or below the band of stability will undergo nuclear decay to achieve stability.
Atoms that lie ABOVE the band of stability have TOO MANY NEUTRONS.
Atoms that lie BELOW the band of stability have TOO MANY PROTONS.

20. Three Basic Types of Radiation
Alpha (α) He2+
Beta (β) e
Gamma (g) g 4 2 -1

21. Alpha Particles (42He2+) Weakest form of radiation
Helium nucleus: 2p+, 2no, 0e-
Stopped by skin – found in cigarette smoke

22. Alpha Particles break off

23. Alpha decay (42He) U He Th 238 92 4 2 234 90 + Alpha particle
is released.
238 – 4 = 234
92 – 2 = 90

24. Beta Particles (0-1e) Medium strength
A neutron splits into a proton and an electron
Proton stays in nucleus, electron is emitted

25. Beta Particles (0-1e)
6 protons
8 neutrons
7 protons
7 neutrons

26. Write Equations for the Following:
A Beta decay for Radium-226
226 88 -1
226 89 Ra
e + Ac

27. Gamma Radiation 00g No particle is released, just energy.
Strongest form of radiation – very penetrating.

28. Gamma Radiation (00g)

29. Write Equations for the Following:
A Gamma decay for Thorium-234
234 90
234 90
g + Th
Th*

30. Writing Nuclear Equations:
Use symbol notation
Mass numbers and atomic numbers must be equal on each side of the arrow…Law of Conservation of Mass

31. Write Equations for the Following:
An Alpha decay for Potassium-45
A Beta decay for Radium-226
A Gamma decay for Thorium-234 45 19 41 17 4 2 K Cl
+ He
226 88 -1
226 89 Ra
e + Ac
234 90
234 90 Th
Th + g

32. Comparing Decay Particles

33. Half-Life Every radioisotope has a characteristic rate of decay.
This rate of decay is measured by the half-life of that radioisotope.

34. Half-Life
A half-life is the time required for one half of a radioisotope’s nuclei to decay.
In other words:
After each half-life of a radioisotope, half of the original radioactive atoms have decayed into atoms of a different element.

35. Initial amount of radio- isotope
100%
Initial amount of radio- isotope
50%
25%
Amount after 1 half-life
12.5%
Amount after 2 half-lives
Amount after 3 half-lives

36. This new element may be another radioisotope, or a stable isotope.
As a radioisotope decays a new element is formed by the decayed portion of the radioisotope after each half life.
This new element may be another radioisotope, or a stable isotope.
Radioactive decay continues until a stable isotope is formed. This process creates a radioactive decay series.

37. This set of data is a radioactive decay series.
Lets follow the half-lives of Uranium-238
This set of data is a radioactive decay series.

38. n is the number of half-lives
Example 1:
Carbon-14 has a half life of 5.73 x 103 years. If you begin with 48g sample, how much carbon-14 will you have left after 2 half-lives?
Original mass x (1/2)n = Remaining mass
n is the number of half-lives
48g x (1/2)2 = 12g of Carbon-14

41. Example 2:
A 464g sample of Thorium-234 is known to be 144 days old. Thorium-234 has a half-life of 24 days. How many grams of Thorium remain?
Total time / duration of half-life = # of half-lives
144 days / 24 days = 6 half-lives
464 g x (1/2)6 = 7.25g

42. Example 2:
An original 5.00 g sample of Hydrogen-3 (Tritium) has 3.90 x 10-2 g of Tritium remaining in the sample. If the half-life of Tritium is years, how old is the sample?
5.00 g x (1/2)n = 3.9 x 10-2 g
(1/2)n = 3.9 x 10-2 g
5.00 g
(1/2)n = 1/128
n = 7
7 half lives x years = 86.2 years

43. Nuclear Decay
Every radioactive isotope will break apart (decay) at a unique rate.
Half-life is the time required for the mass of an isotope to decrease by half.
ex. The t 1/2 of X is 2 hrs. Of a 100g sample, how much will be left in 6 hrs.?
100g hrs.
50g hrs.
25g hrs.
12.5g hrs.

44. Half-Life example 1
The half-life of Radium-230 is 2.5 hours. How much of a 50.0 g sample will remain after 10 hours?
50g hrs
25g hrs
12.5g hrs
6.25g hrs
3.125g hrs

45. Half-Life example 2
The initial mass of an unknown isotope is g. After 15 days, its mass is only 12.5 g. What is the half-life of this isotope?