1. The Atom

2. Basic Atomic Theory  Atom = “indivisible” in Greek  Atoms are indivisible and indestructible  Atoms of same element are identical  Compounds are formed by a combination of two or more different kinds of atoms  Chemical reactions cannot change one element into another  Atoms only rearrange

3. Atoms are Indivisible and Indestructible? NNot true! WWhy? NNuclear reactions SSubatomic particles

4. Electrons  Discovered by J.J. Thompson using a cathode ray tube  Negatively charged (-1)  Electron’s mass is 1/1840  Free moving around the nucleus

5. Protons  Discovered by Moseley  Positively charged (+1)  Proton’s mass is 1 (About 2000 times more than an electron)  Atomic # = # protons  No 2 elements have the same # of protons  Found in the nucleus of an atom

6. Neutrons  Discovered by Chadwick  No charge  Same mass as proton (1)  Found in the nucleus of an atom

7. Atomic Number  Whole number  Atomic # = # of proton  Atomic # = # of electrons (neutral)  Atomic # = Z  Shorthand nuclear symbol  Unique for every element

8. Atomic Number

9. Mass Number  Whole number  Mass # = # of protons + # of neutrons  Mass # = A  Shorthand nuclear symbol  Isotopes of the same element have different mass #  Isotopes are the different kinds of atoms within one element (C-12 and C-13)

10. Mass Number

11. Using Mass Number  Mass # = # of protons + # of neutrons  To find # of protons  # protons = # electrons (neutral atom)  Need to know mass # and # of neutrons  To find # of neutrons:  Need to know mass # and # of protons

12. Nuclear Shorthand  Top number is A (mass #)  Element symbol in the middle  Bottom number is Z (atomic #) Z A Element Symbol

13. Atomic Mass LListed on periodic table DDoes not equal mass # GGiven in atomic mass units (amu) 11 amu = 1/12 the mass of C-12 atom IIs not a whole number DDue to relative abundance of naturally occurring isotopes WWeighted average

14. Finding Atomic Mass  To calculate the atomic mass of an element  Multiply the mass of each isotope by its percent abundance (expressed as a decimal)  The quantity of a specific isotope that occurs in a natural sample of an element  Add the masses together  Also called average atomic mass

16. Isotopes AAtoms of the same element HHave the same # of protons and electrons HHave a different number of neutrons HHave a different mass number HHave the same physical and chemical properties and undergo the same chemical reactions HHave differing nuclear qualities SSome isotopes of an element may be radioactive AAverage atomic mass takes all of the isotopes into consideration

18. Ions  Atoms are neutral  Equal number of protons and electrons  Atoms can become charged by gaining or losing an electron  Called ions  Ions are indicated with a (+) or (-) sign  Cations are positive  Anions are negative

19. Cations and Anions