Elements and isotopes

Physical Science

1. rECAP 3 REACTIONS THAT LED TO THE FORAMTION OF THE ELEMENTS: NUCLEOSYNTHESIS FUSION NEUTRON CAPTURE REACTION REACTION REQUIRED A CERTAIN AMOUNT OF ENERGY TO PROCEED

2. Elements and isotopes MODULE 2

3. 1. Describe how elements heavier than iron are formed. 2. Describe how isotopes are formed; 3. Discuss the significance of isotopes to mass number; and 4. Solve problems on percent abundance of elements. LEARNING OBJECTIVES:

4. I. ELEMENTS Over 100 different types of atoms exist and each atom is called an element.

5. I. ELEMENTS Atomic mass (A) is the mass of element. Number of protons + number of neutrons Atomic number (z) is the number of protons. Fingerprint of the element

6. I. ELEMENTS An element can have different number of electrons or neutrons but always has the same number of protons.

7. II. ISOTOPES Isotopes are atoms of the same element that have the same atomic number (z) but different mass number (A). Examples : 6 7 8 Li Li Li      

8. Isotope Notation One way to identity the different isotopes of an element is through a symbol called isotope notation . It has four parts: element symbol ( X ), mass number ( A ) atomic number ( Z ) Charge of the atom ( e ) A = mass number ( protons + neutrons) Z = atomic number ( number of protons ) e = atomic charge ( protons - electrons ) In general, the isotope notation for an element can be expressed as follows: A e Z For example, the isotope notation for a neutral uranium atom with 146 neutrons can be written as follows: 238 92 x U Proton= 92 Neutron=146 (given) 92+146= 238 amu (mass number/atomic mass) Uranium-238 or U-238

9. Isotopes and Mass Numbers of Elements Deuterium & Tritium a re isotopes of hydrogen , but they behave chemically, like any other hydrogen atoms. Figure of Atomic structure and isotope notation of the different isotopes of hydrogen. 2.014 amu 3.016 amu Therefore, you can represent hydrogen isotopes as H-1 for protium , H-2 for deuterium , and H-3 for tritium.

10. Atomic Mass and Isotopic Abundance Carbon has three (3) fundamental isotopes: carbon-12, carbon-13, and carbon-14 Carbon-12 or C-12 is the most common and the lightest among the carbon isotopes.

11. Example 1: Magnesium has three isotopes: Mg , Mg , Mg . They occur naturally with a percentage abundance 0f 78.6%, 10.1% and 11.3%, respectively. The exact masses of these isotopes are 23.9924, 24.9938, and 25.9898. What is the weighted average of the three isotopic masses? 24 25 26 Solution: ( 1 ) Write the following equation : Weighted average = (mass of Mg -24) (abundance of Mg-24) + (mass of Mg - 25) (abundance of Mg-25) + ( mass of Mg - 26) (abundance of Mg-26) ( 2 ) Solve for weighted average weighted average= (23.9924)(78.6) + (24.9938)(10.1 ) + (25.9898) (11.3) 100 = 24.32

12. Thank you!

13. MODULE 2: Elements and Isotopes Activities Answer the following activities below using your textbook. Write it on a long bond paper. Don’t forget to write your name, module # & title, Activity and page. What Have I Learned So Far? Page 10 What Have I Learned So Far? Pages 13