1. Reminders Lab Equipment Quiz is TOMORROW! DAILY QUIZZES begin today –Up to three questions regarding something we have already covered in class: measurement, conversions, matter, atomic structure. –This week, questions will come from the MATTER STUDY GUIDE

2. Daily Quiz – 2 nd Hour WRITE YOUR ANSWERS ONLY. Classify the following as a physical or chemical change. NO COMMUNICATING. 1.Dead leaves decaying 2.Rain puddle drying up 3.Gasoline evaporating Chemical Physical

3. Calculating Atomic Mass

4. I. Important features of the Periodic Table A.Most periodic tables list the element name and their symbol. Element – a substance that cannot be broken down into simpler substances Element Symbol – a one, two, or three letter combination that symbolizes a specific element

5. 1.Element symbols mostly are either one or two letters. The first letter is always capitalized and the others are lowercase 2. Some element symbols are made of letters that aren’t in their name because they were named in another language like Greek or Latin.

6. B. The elements are placed in order of increasing atomic number. 1. As atomic number increases so does the atomic mass of the elements. Atomic mass – the sum of the neutrons and protons in the nucleus of an atom

7. Atomic Mass Units (amu) – atomic mass units

8. II. Isotopes A.The atomic mass of an element is an average of all the naturally occurring of the element Isotopes – atoms of an element that have the same atomic number but different numbers of neutrons

9. B. Isotopes of the same element can be represented with different symbols: Element name-mass number (i.e. Carbon-12) A Element z Symbol A – Mass Numberz – atomic number

10. III. Calculating Average Atomic Mass A. The presence of isotopes makes it difficult to calculate an element’s mass number because each isotope has a different atomic mass

11. B. The atomic masses on the periodic table represent the weighted average atomic mass of all isotopes of a given element

12. 1. To calculate average atomic mass you will need to know the % abundance of each isotope in a sample of an element

13. Example Problems 1.A sample of Ca is 90% Calcium-40 and 10% Calcium-41. What is the average atomic mass? 90% Calcium-40 = (.90)(40) = 36 10% Calcium-41 = (.10)(41) = 4.1 36 + 4.1 = 40.1g

14. 2. A sample of Chlorine has two isotopes. Chlorine-35 and Chlorine-37. Chlorine-35 has an actual mass of 34.9689 amu and Chlorine-37 has a mass of 36.9659 amu. In any sample of chlorine atoms, 75.771% will be chlorine-35 and 24.229% will be chlorine-37. Calculate the average atomic mass of chlorine.

15. Pick out important information. Chlorine-35 75.771% abundance Chlorine-37 24.229% abundance 34.9689 x.75771 36.9659 x.24229 + 8.9564726.49629 35.45276 amu