1. 1 THE ATOM

2. NUCLEAR MODEL OF THE ATOM An atom is an electrically neutral particle Composed of protons, neutrons, and electrons. Atoms are spherical in shape Have a tiny, dense nucleus of positive charge surrounded by one or more negatively charged electrons Nucleus contains 99.7 % of the mass of an atom. 2

3. BASIC STRUCTURE OF THE ATOM 3

4. SUBATOMIC PARTICLES 4

5. Most of the atom consists of fast-moving electrons traveling through the space around the nucleus. Atoms are neutral in charge The number of protons = the number of electrons Atomic Number: The number of Protons in the nucleus determines the identity of an atom No two types of atoms have the same number of protons An Element consists of atoms with the same number of protons. 5

6. ATOMIC NUMBER(Z): THE NUMBER OF PROTONS IN THE NUCLEUS OF EACH ATOM OF THE ELEMENT Atomic Number = Protons Elements are arranged in the periodic table from left to right in order of increasing atomic number. Atomic number identifies the element 6

7. ISOTOPES AND MASS NUMBER Atoms can have different mass. Naturally occurring elements are a mixture of atoms that have different numbers of neutrons. Atoms with the same number of protons, but different number of neutrons are called Isotopes. 7

8. HYDROGEN HAS THREE ISOTOPES: Protium1 proton1 electron0 neutrons Deuterium1 proton 1 electron1 neutron Tritium1 proton1 electron2 neutrons 8

9. ISOTOPES AND MASS NUMBER Isotopes: atoms of the same element that have different masses. Same number of protons Different number of neutrons Different Mass name and mass. Atoms of different isotopes have different masses so identity is given by name and mass. Mass Number = protons and neutrons 9

10. ISOTOPE (NUCLEAR) SYMBOLS: Consists of three parts 1.the symbol of the element 2.the atomic number of the element 3.the mass number of the specific isotope. 10

11. NUCLEAR SYMBOL Read as Helium-4 11

12. ISOTOPE NAMES Element Name-Mass Number Helium-4 Potassium-39 Hydrogen-3 12

13. NEUTRONS = MASS NUMBER – ATOMIC NUMBER Atomic Number: _________ Mass Number: __________ # of Protons: _________ # of Electrons: _______ # of Neutrons: ________ Name of Isotope: ____________ 13

14. EXAMPLE Atomic Number: _________ Mass Number: __________ # of Protons: _________ # of Electrons: _______ # of Neutrons: ________ Name of Isotope: ____________ 14

15. EXAMPLE 15 Atomic Number: _________ Mass Number: __________ # of Protons: _________ # of Electrons: _______ # of Neutrons: ________ Isotope Name: _________

16. DRAW THE ISOTOPE SYMBOL FOR CALCIUM WITH 21 NEUTRONS. 16

17. COMPARING POTASSIUM ISOTOPES Potassium-41 protons = ________ electrons = ______ neutrons = _______ Potassium-40 protons = ________ electrons = ______ neutrons = _______ Potassium-39 Protons = __________ Electrons = _________ Neutrons = __________ 17

18. RELATIVE ATOMIC MASSES Atomic masses measured in grams are very small. Example: An atom of Oxygen-16 has a mass of 2.657 x 19 -23 grams. It is most convenient to measure mass in relative atomic masses. 18

19. TO SET UP A RELATIVE SCALE OF ATOMIC MASSES: 1.One atom is chosen and assigned a relative mass value, 2.All the other masses are expressed in relation to this defined standard. Carbon-12 is the chosen standard. A single atom of C-12 is assigned a mass of exactly 12 atomic mass units(u). 19

20. AN AMU One amu is exactly 1/12 th of the mass of a carbon- 12 atom or 1.660 5402 x 10 -24 grams. The atomic mass of a carbon-12 atom is exactly 12 u. Atomic Mass: The mass of an atom expressed in atomic mass units. 20

21. AVERAGE ATOMIC MASS Atomic Masses given for the elements on the periodic table are weighted averages for the naturally occurring mixtures of isotopes, called average atomic mass. Average Atomic Mass depends on mass and relative abundance of the isotopes. 21

22. TO CALCULATE AVERAGE ATOMIC MASS: 1.Atomic mass x relative abundance 2.Add results. 22

23. EXAMPLE PROBLEM: Naturally occurring copper consists of 69.17% Cu-63, mass of 62.939 598u and 30.83% Cu-65, mass of 64.927 793u 0.6917 x 62.939 598u = 43.535u 0.3083 x 64.927 793u =20.017 23