2. Atomic Structure nucleusproton (+) Neutron (o) Electron (-)

3. Nucleus: at the center of the atom Protons: - are positively charged - are the same in number as the atomic number - equal the number of electrons in a neutral atom Neutrons: - are neutral - number varies (# neutrons = mass # - atomic #)

4. Electrons are negatively charged move at high speed in “shells” around the center of the atom Electrons are not confined to a certain path, but will be found within a “cloud”, or orbital area

5. Determining the numbers of particles in each element How many protons, electrons and neutrons are in each of these atoms? Be Ne Na Ag Pb 4 + 4 - 5 o 10 + 10 - 10 o 11 + 11 - 12 o 47 + 47 - 61 o 82 + 82 - 125 o

6. Bell work 12-7 How many protons neutrons and electrons does Sulfur have?

7. Isotopes Atoms that have the same number of protons, but a different number of neutrons Example: Neon: 10 electrons 10 protons 10 neutrons Neon-21: 10 protons 10 electrons 11 neutrons Neon-22 10 protons 10 electrons 12 neutrons

8. Atomic mass The atomic mass is actually the average of the isotopes of each element Example: Element X has two natural isotopes. The isotope with a mass of 10.012 amu ( 10 X) occurs 19.91% of the time in the earth’s crust. The isotope with a mass of 11.009 amu ( 11 X) occurs 80.09% of the time in the earth’s crust. Calculate the atomic mass of element X.

9. Here’s how to solve it: 10 X: 10.012 amu X 0.1991 = 1.993 amu 11 X: 11.009 amu X 0.8009 = 8.817 amu Atomic mass of element X = 10.810 amu

10. Try this one: Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundances of 78.92 amu (50.69%) and 80.92 amu (49.31%). Answer: 79.90 amu

11. Here’s how they’re written: Element symbol 6 C 14 Atomic mass Atomic number (# of protons) So – the number of neutrons is… 8