1. Particles in the Atom Each element is chemically unique. To understand why they are unique, you need to know the structure of the atom (the smallest particle of an element) and the characteristics of its components.

3. Electrons (-) charge no mass located outside the nucleus Protons (+) charge 1 amulocated inside the nucleus Neutrons no charge 1 amulocated inside the nucleus Particles in the Atom

4. electronsprotonsneutrons Atoms consist of electrons, protons, and neutrons. 1. Electrons and protons have electrical charges that are identical in magnitude but opposite in sign. Relative charges of  1 and +1 are assigned to the electron and proton, respectively. 2. Neutrons have approximately the same mass as protons but no charge—they are electrically neutral. 3. The mass of a proton or a neutron is about 1836 times greater than the mass of an electron. Protons and neutrons constitute the bulk of the mass of the atom. Particles in the Atom

5. Humor Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!” The other says, “Are you sure??” “Yes, I’m positive!” A neutron walks into a restaurant and orders a couple of drinks. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”

6. Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ nono +1 0 1/1840 1 1 9.11 x 10 -28 1.67 x 10 -24

7. Structure of the Atom There are two regions The nucleus With protons and neutrons –Positive charge –Almost all the mass Electron cloud –Most of the volume of an atom –The region where the electron can be found

8. Subatomic Particles Most of the atom’s mass. NUCLEUS ELECTRONS PROTONS NEUTRONS Negative Charge Positive Charge Neutral Charge ATOM QUARKS Atomic Number equals the # of... equal in a neutral atom Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

9. Subatomic Particles Most of the atom’s mass. NUCLEUS ELECTRONS PROTONS NEUTRONS Negative Charge Positive Charge Neutral Charge ATOM QUARKS Atomic Number equals the # of... equal in a neutral atom Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

10. Size of an atom Atoms are incredibly tiny. Measured in picometers (10 -12 meters) –Hydrogen atom, 32 pm radius Nucleus tiny compared to atom –Radius of the nucleus near 10 -15 m. –Density near 10 14 g/cm 3 IF the atom was the size of a stadium, the nucleus would be the size of a marble. California WEB

11. Counting the Pieces Atomic Number = number of protons # of protons determines kind of atom Atomic Number = number of electrons in a neutral atom Mass Number = the number of protons + neutrons California WEB 12 6 C 14 6 C 12 6 C Mass Number = A Atomic Number = Z