1. How many protons, electrons, and neutrons are in an atom?

2. Step 1 Use your periodic table to find an element

3. Step 2 The number of Protons (+ charge) The atomic number = # protons
Kr has 36 protons

4. Step 3 The number of Electrons (- charge)
Remember atoms have no overall charge.
Atoms must have an equal # of protons and electrons
#protons=#electrons
Kr has 36 electrons

5. Step 4 Neutrons = Mass # - Protons The number of Neutrons (no charge)
Mass # (atomic weight rounded to nearest whole #)
Neutrons = Mass # - Protons
Neutrons = 84 – 36
Neutrons = 48

6. Summary Number of Protons = Atomic # Number of Electrons = Protons
Number of Neutrons = Mass # - Protons

7. Problems Find the protons (p+), electrons (e-), neutrons (n) of Oxygen
Find the p+, e-, n of Xenon (Xe)
Find the p+, e-, n of Zirconium (Zr)

8. Oxygen (O) p+, e-, n Number of Protons = Atomic #
Number of Electrons = Protons
Number of Neutrons = Mass # - Protons
Protons = 8
Electrons = 8
Neutrons = 16-8 = 8

9. Xenon (Xe) p+, e-, n Number of Protons = Atomic #
Number of Electrons = Protons
Number of Neutrons = Mass # - Protons
Protons = 54
Electrons = 54
Neutrons = = 77

10. Zirconium (Zr) p+, e-, n Number of Protons = Atomic #
Number of Electrons = Protons
Number of Neutrons = Mass # - Protons
Protons = 40
Electrons = 40
Neutrons = = 51