1. The Atom Three Basic Particles

2. Proton Nucleus of atom Positive charge # of protons (p + ) = atomic number Contain much of the mass of the atom

3. Neutron Nucleus of atom Nucleus of atom No charge (neutral) No charge (neutral) Mass # = # of protons + # of neutrons (n o ) Mass # = # of protons + # of neutrons (n o ) Help to keep the nucleus stable Help to keep the nucleus stable The number of neutrons determines the isotope of the element The number of neutrons determines the isotope of the element Contain much of the mass of the atom Contain much of the mass of the atom

4. Electron Orbiting outside of the nucleus Orbiting outside of the nucleus Electrons (e - ) can be added or removed from atoms to create ions and form chemical bonds Electrons (e - ) can be added or removed from atoms to create ions and form chemical bonds Negative charge Negative charge # of e - = # of p + (in a neutral atom) # of e - = # of p + (in a neutral atom) Very negligible mass Very negligible mass protons and neutrons are roughly the same mass as each other and are about 1800 times heavier than electrons protons and neutrons are roughly the same mass as each other and are about 1800 times heavier than electrons

5. How small are atoms? TRY THIS !!! If the radius of a sodium atom is 186 picometers, then calculate the # of sodium atoms that would line up side by side on a line that is 5.00 cm long … (Hint: 1 pm = 10-10 cm)

6. Ready for the answer?

7. 134 408 602 WOW!!!

8. How did you get that? 1)Radius x 2 = Diameter 186 pm x 2 = 372 pm 2)5.00 cm=5.00 cm= 372 pm0.0000000372 cm 134 408 602 sodium atoms!!

9. More about Isotopes Isotopes  atoms of the same element that have different masses are called isotopes  Different masses are caused by different numbers of neutrons  Example: Uranium–235 and Uranium–238 Both are Uranium, so both have 92 protons, but U-235 has 143 neutrons and U-238 has 146 neutrons (so the U-238 isotope is a little bit heavier)

10. Isotope Symbols U-238 U-238 Mass Number (# of protons + # of neutrons) 238 92 U Mass Number (# of protons + # of neutrons) Atomic Number (# of protons) Al 3+ Charge (lost 2 electrons) to make a positive ion 26 13