1. Section III: A World of Particles
Lesson 11 Atomic Pudding
Lesson 12 Atoms By Numbers
Lesson 13 Subatomic Heavyweights
Lesson 14 Isotopia
Lesson 15 Nuclear Quest
Lesson 16 Old Gold

2. Day 18 Lesson 11: Atomic Pudding
Models of the Atom

3. Day 18 ChemCatalyst
The drawing shown here is a model of a very tiny cube of gold.
1. What do you think a scientific model is?
2. The spheres in this model represent atoms. What do you think atoms are?
3. How could you draw a model of the element copper to show that it is different from the element gold?
meter

4. You will be able to:
describe the historical development of the current atomic model
describe and draw an atomic model and explain the evidence that supports the existence of atomic structures
describe the dynamic nature of scientific models

5. Prepare for the Activity
Work in groups.
Model: A simplified representation of something more complex, that facilitates understanding certain aspects of a real object or process.
Atoms: The smallest unit of an element that retains the chemical properties of that element.

6. Discussion Notes
The Atomic Model Through Time

7. Discussion Notes (cont.)
Contemporary scientists are in agreement that matter is made up of tiny particles called atoms.

8. Discussion Notes (cont.)
Nucleus: The dense, positively charged structure found in the center of the atom. It is composed of protons and neutrons.
Proton: A particle with a positive charge, found in the nucleus of atoms.
Electron: A particle with a negative charge. Electrons move very fast around the outside of the nucleus of atoms.
Neutron: A particle that does not have a charge, found in the nucleus of atoms.

9. Discussion Notes (cont.)
Scientists have created models to describe atoms.
Scientific evidence is a collection of observation that everyone agrees on.

10. Wrap Up How are the smallest bits of matter described?
All matter is made up of extremely small particles called atoms. These particles are too small to be seen directly, even under a microscope.
The atom is composed of even smaller particles called protons, neutrons, and electrons. The protons and neutrons are located in the dense nucleus of the atom. The electrons surround the nucleus. Protons are positively charged, neutrons have no charge, and electrons are negatively charged.

11. Wrap Up (cont.) Science is theoretical and dynamic.
Models and theories are continually being revised or replaced with new models and theories as new evidence is gathered.

12. Day 19 Lesson 12: Atoms By Numbers
Atomic Number and Atomic Mass

13. Day 19 ChemCatalyst
Models of a helium atom and a beryllium atom are shown. The nucleus of each contains protons and neutrons. The electrons orbit the nucleus.
1. Compare the two models. List three similarities and three differences.
Based on the models, why do you think helium is number 2 (the second element) and beryllium number 4 (the fourth element) on the periodic table?

14. Key Question
How are the atoms of one element different from those of another element?

15. You will be able to:
distinguish between atomic number, mass of an atom, and average atomic mass
describe the structure of an atom and draw a simple atomic model of an atom
extract information from the periodic table related to atomic structure and atomic mass

16. Prepare for the Activity
Work in groups.

17. Discussion Notes
The atomic number of an element is the same as the number of protons in the nucleus of that element.
Atomic number: The number of protons in the nucleus of an atom of an element. In the periodic table, the elements are arranged in order by atomic number.

18. Discussion Notes (cont.)
The atomic mass of an atom determined by summing the number of protons and neutrons is not identical to the average atomic mass of the element given in the periodic table.
If you change the number of protons in an atom, you also change the elemental identity of that atom.

19. Discussion Notes (cont.)
Each successive element has one more proton than the element before it.
Protons and neutrons account for most of the mass of an atom.
You can estimate the number of neutrons in an atom by subtracting the number of protons from the average atomic mass of the element (rounded to the nearest whole number).

20. Wrap Up
How are the atoms of one element different from those of another element?
Each element in the periodic table has one more proton than the element preceding it.
The atomic number of an element is the same as the number of protons in the nucleus of each of its atoms.

21. Wrap Up (cont.)
In a neutral atom, the number of electrons is equal to the number of protons.
The mass of a proton is 1 atomic mass unit (1 amu). The mass of a neutron is also 1 amu. The mass of an electron is so small it is considered negligible. So the mass of an atom in atomic mass units is simply the sum of the number of protons and the number of neutrons.

22. Day 20 Lesson 13: Subatomic Heavyweights
Isotopes

23. Day 20 ChemCatalyst Here is a model of a carbon atom.
1. List two things this model tells you about the carbon atom.
2. List something this model does not tell you about the carbon atom.

24. Key Question
How can atoms of the same element be different?

25. You will be able to:
define isotope and write and interpret the symbol for a specific isotope
determine the average atomic mass of an element based on the natural abundance of isotopes of that element
predict the number of protons, neutrons, and electrons in the most abundant isotope of an atom, based on average atomic mass

26. Prepare for the Activity
Work in pairs.

27. Discussion Notes
Atoms of the same element that have different numbers of neutrons are called isotopes.
The percentage of each isotope of an element that occurs in nature is called the natural percent abundance of the isotope.

28. Discussion Notes (cont.)
Symbols Associated with Isotopes

29. Discussion Notes (cont.)
Chemists use a special notation to symbolize an isotope.
One way to refer to isotopes is to use their mass numbers.

30. Discussion Notes (cont.)
Calculate the Atomic Mass of Neon

31. Discussion Notes (cont.)
The average atomic mass of an element is the weighted average of the masses of the isotopes in a sample of the element.
The most common isotope of an element, frequently has a mass that is close to the average atomic mass given in the periodic table.

32. Wrap Up How can atoms of the same element be different?
Isotopes of an element have the same number of protons and electrons but different numbers of neutrons.
The average atomic mass of an element listed in the periodic table is the weighted average mass of the naturally occurring isotopes of that element.
Isotopes are referred to by their mass numbers, as in carbon-12.

33. Day 21 Lesson 16: Old Gold
Formation of Elements

34. Day 21 ChemCatalyst
Use your periodic table to identify these elements.
Atomic number is 18.
Has three electrons when atoms are neutral.
Atomic mass is 16.0.

35. Key Question
How are new elements formed?

36. You will be able to:
explain how different elements are formed through nuclear reactions
write a balanced nuclear equation
describe the mechanism behind a nuclear chain reaction

37. Prepare for the Activity
Work individually.
You will need a copy of the periodic table and the isotope chart and nuclear reactions table.

38. Discussion Notes
Nuclear processes can be written as nuclear equations.
During alpha decay, the nucleus of an atom emits a helium nucleus, transforming the element into an element with a smaller nucleus.
During beta decay, a neutron inside the nucleus of an atom emits an electron.

39. Discussion Notes (cont.)
Nuclear fusion involves the joining together of nuclei.
Fission involves a nucleus breaking up into smaller nuclei.
Nuclear reactions change the identity of an element.
Nuclear fusion produces bigger (heavier) elements from smaller (lighter) ones.

40. Discussion Notes (cont.)
Nuclear Chain Reactions

41. Discussion Notes (cont.)
Nuclear fission is a process that releases enormous amounts of energy.
Nuclear fission can result in a nuclear chain reaction that produces a great deal of energy.

42. Wrap Up How are new elements formed?
Radioactive decay, nuclear fusion, and nuclear fission are all nuclear processes that result in the creation of new elements.
The mass of a nucleus changes when neutrons or protons are added or lost.
The identity of an element changes when its nucleus gains or loses protons.

43. Wrap Up (cont.)
Radioactive decay happens in the natural world around us. Fission can be spontaneous for unstable nuclei, or it can be provoked using nuclear bombardment and other methods. Fusion of nuclei to form different isotopes happens in the stars.

44. Day 22 ChemCatalyst
Nitrogen has two naturally occurring isotopes. Predict the number of neutrons in the two isotopes of nitrogen, N by looking at the average atomic mass for N.
Which isotope do you predict to be more abundant? How do you know?

45. Day 23 ChemCatalyst
A chemist investigating a sample of lithium found that some lithium atoms have a lower mass than other lithium atoms. The chemist drew models of the two different types of lithium atoms, as shown on the following slide.

46. Day 23 ChemCatalyst (cont.)
What is different about the two atoms?
What is the atomic number of each atom?
What is the atomic mass of each atom?