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

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

Step 1 Use your periodic table to find an element

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

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

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

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

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)

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

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

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

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