1. Drill
What is Ernest Rutherford’s contribution to atomic theory?

2. Objective
SWBAT:
Analyze Isotopes in order to calculate atomic mass.

3. SAT/HSA Enrichment
A measurement consists of…certain digits, one uncertain digit, and …
a. an appropriate number of … a unit.
b. an even number of …a decimal point.
c. an odd number of …a decimal point.
d. at least three … a unit.
e. never more than one or two …. a unit.

4. Focus Questions How may atoms of an element differ?
What is the same about these atoms and what is different since they are all carbon.
Define isotope from this discussion.
Carbon-12
Carbon-13
Carbon-14

5. Distinguishing Among Atoms
Difference b/w Atoms

6. Distinguishing Among Atoms
Just as apples come in different varieties, a chemical element can come in different “varieties” called isotopes.

7. Atomic Number
Elements are different because they contain different numbers of protons.
The atomic number of an element is the number of protons in the nucleus of an atom of that element.

8. Atomic Number

9. Conceptual Problem

10. Conceptual Problem

11. Mass Number
The total number of protons and neutrons in an atom is called the mass number.
The number of neutrons in an atom is the difference between the mass number and atomic number.

12. Mass Number
Au is the chemical symbol for gold.
Mass #
Atomic #

13. Sample Problem

14. Sample Problem

15. Sample Problem

16. Isotopes
Isotopes are atoms that have the same number of protons but different numbers of neutrons.
Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.

17. Isotopes
Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons.

18. Atomic Mass
It is useful to compare the relative masses of atoms to a standard reference isotope. Carbon-12 is the standard reference isotope. Cabon-12 has a mass of exactly 12 atomic mass units.
An atomic mass unit (amu) is defined as one twelfth of the mass of a carbon-12 atom.

19. Some Elements and Their Isotopes

20. Atomic Mass
The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.
A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.

21. Atomic Mass
Weighted Average Mass of a Chlorine Atom

22. Atomic Mass
To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

23. Atomic Mass For example, carbon has two stable isotopes:
Carbon-12, which has a natural abundance of 98.89%, and
Carbon-13, which has a natural abundance of 1.11%.

24. Sample problem

25. Sample problem

26. Sample problem

27. The Periodic Table—A Preview
A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties.
A periodic table allows you to easily compare the properties of one element (or a group of elements) to another element (or group of elements).

28. The Periodic Table—A Preview

29. The Periodic Table—A Preview
Each horizontal row of the periodic table is called a period.
Within a given period, the properties of the elements vary as you move across it from element to element.

30. A Period

31. The Periodic Table—A Preview
Each vertical column of the periodic table is called a group, or family.
Elements within a group have similar chemical and physical properties.

32. A Group or Family

33. The Atomic Mass of Candium
Small Scal Lab:
Purpose
To analyze the isotopes of “Candium” and to calculate its atomic mass.
30 MIN

34. Summary Did we accomplish the objective? Explain. Define Atomic Mass?
Define Isotope?
How are isotopes alike? How are they different?
Determine the difference between carbon-12, carbon-13 and carbon-14.

35. Homework
Complete Distinguishing Between Atoms worksheet.