Chapter 4: Atomic Structure

1. Chapter 4: Atomic Structure Section 3 - Distinguishing Among Atoms pgs. 110-119

2. The Atomic Model • Based on experimental evidence: • The atom is ________________________. • All the _______________, and almost all the _________ is concentrated in a small area in the center called the ______________ • The nucleus is composed _______________ ________________________________ • Protons are ___________________________ • Neutrons are __________________________

3. The Atomic Model • The electrons _________________________ ____________________________________ • Electrons are _________________________ • This model was called the _______________ • All atoms are composed ______________ __________________________________

4. Atomic Structure • How then are atoms of one element different from another element? • Elements are different because ______ _________________________________ • The “________________” of an element is the _______________ in the nucleus • # ______ in an atom = # _______

5. Section 4-3 Distinguishing Among Atoms Introduction to the Periodic Table

6. B. ______________ C A.____________ D._______________ C. ___________ Section 4-3 Distinguishing Among Atoms Introduction to the Periodic Table 6 Carbon 12.011

7. Section 4-3 Distinguishing Among Atoms _________________ _________

8. Atomic Number Atomic number of an element is the number of protons in the nucleus of each atom of that element.

9. Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope: __________________ _______ __ __ ____ ________ ____ ___ ____ ____________ __ ___ ____

10. Complete Symbols • Contain the symbol of the element, the mass number and the atomic number. _____ ______ X Superscript → ______ ______ Subscript →

11. Symbols • Find each of these: • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 80 Br 35

12. Symbols • If an element has an atomic number of 34 and a mass number of 78, what is the: • number of protons • number of neutrons • number of electrons • complete symbol

13. Symbols • If an element has 91 protons and 140 neutrons what is the • Atomic number • Mass number • number of electrons • complete symbol

14. Symbols • If an element has 78 electrons and 117 neutrons what is the • Atomic number • Mass number • number of protons • complete symbol

15. Isotopes • Not all atoms of an element are _____________. • Atoms of the same element can have ________________________. • Thus, the atoms have: • The same __________________________ • different __________________________. • These are called _____________.

16. Naming Isotopes • Isotopes can be designated by putting the mass number after the element name: • carbon-_____ • carbon-_____ • uranium-_____

17. Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.

18. Isotopes Elements occur in nature as ____________ ____________.

19. Atomic Mass • How heavy is an atom of oxygen? • It depends, because ______________ _______________________________. • We are more concerned with the ______ _______________________________ • This is based on the ________________ _________________________________ _________________________________ • We don’t use grams for this mass because the numbers would be too small.

20. Measuring Atomic Mass • Instead of grams, the unit we use is the ______________________ • It is defined as ______________ __________________________. • Carbon-12 chosen because _______________. • Each isotope has its own atomic mass, thus we determine the average from percent abundance.

21. To calculate the average: • Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results. • If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)

22. Atomic Masses Atomic mass is the average of all the naturally occurring isotopes of that element. Carbon = 12.011 amu

23. Calculating Average Atomic Mass • Example: What is the atomic weight of a hypothetical element consisting of two isotopes, one with mass = 64.23 amu (26.00%), and one with mass = 65.32 amu?

24. Calculating Average Atomic Mass • Example: A hypothetical element consists of the following naturally occurring isotopes. What is the atomic weight of the element? Isotopes Mass Abundance 1 46.041 amu 26.00% 2 47.038 amu 58.00% 3 49.034 amu 16.00%

25. Calculating Average Atomic Mass • Lithium has two naturally occuring isotopes. Lithium-6 has an atomic mass of 6.015 amu; lithium-7 has an atomic mass of 7.016 amu. The average atomic mass of lithium is 6.941 amu. What is the percent abundance of Lithium-7?