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Determining the number of atomic particles in an element Step one Find the element on the periodic table. Find oxygen. On your paper WRITE 1. Find the element on the periodic table. Step Two •Find the number of protons (+). 8 O oxygen 15.99 On your paper WRITE 2.Find the number of protons (+). A. Atomic # = number of protons Hint: Find the atomic number. • The atomic number is equal to the number of protons (+) 8 O oxygen 15.99 Eight is the atomic number. •This means oxygen has 8 protons (+). 8 O oxygen 15.99 Check for Understanding • How many protons (+) does copper have? 29 29 Cu Copper protons 63.55 Check for Understanding • How many protons (+) does lead have? 82 82 Pb Lead protons 207.20 Step Three •Find the number of electrons (-). 8 O oxygen 15.99 Hint: Find the atomic number. • The atomic number is equal to the number of electrons (-) in a neutral atom. 8 O oxygen 15.99 Whoa! What is a neutral atom? • Neutral means not positive and not negative. So the number of protons (+) have to equal the number of electrons (-) to cancel each other out. So if eight is the atomic number of oxygen. • Then oxygen has 8 protons (+). • Which means oxygen has 8 electrons (-). 8 O oxygen 15.99 Check for Understanding • The number of + will always EQUAL the number of - in a neutral atom. • # of protons = # of electrons Check for Understanding • How many electrons (-) does copper have? 29 29 Cu Copper electrons 63.55 Check for Understanding • How many electrons (-) does lead have? 82 82 Pb Lead electrons 207.20 On your paper WRITE 3.Find the number of electrons (-). A. # of protons = # of electrons Now What!?! • The atomic number gives us the number of protons (+) and the number of electrons (-). • A.P.E. • Atomic # = Proton # = Electron # Now What!?! • But how do we get the number of neutrons (no charge)? Step four--number of neutrons • To get the the number of neutrons, we have to do TWO things • Round the atomic mass. • Subtract the atomic number from the rounded atomic mass. Where is the atomic mass? •The bottom number is the atomic mass. 8 O oxygen 15.99 What is the atomic mass? • The atomic mass is the average mass of one atom of that element. • One atom of Oxygen has a mass of 15.99 amu. 8 O oxygen 15.99 Round the atomic mass. • To round to the nearest WHOLE NUMBER, you look at the tenths column.. 8 For oxygen, the O oxygen number in the tenths column is 9 15.99 Round the atomic mass. • If the number in the tenths column is 5, 6, 7 , 8 or 9…you add one to the ones column. 8 For oxygen, the O oxygen rounded amount is 16. 15.99 Round the atomic mass. • If the number in the tenths column is 4, 3, 2, 1 or 0, you simply drop the decimals. For magnesium, 12 the rounded Mg magnesium amount is 24. 24.30 Okay, so we have rounded the atomic mass..NEXT? • To get the the number of neutrons, we have to do TWO things • Round the atomic mass. • Subtract the atomic number from the rounded atomic mass. Subtract the atomic number from the rounded atomic mass. • The rounded atomic mass for oxygen is 16. •The atomic number is 8. 16 8 - 8 _________ O 8 oxygen 15.99 So the number of neutrons is … 8. • The rounded atomic mass for oxygen is 16. •The atomic number is 8. 16 8 - 8 _________ O 8 neutrons oxygen 15.99 On your paper WRITE 4. To find the number of neutrons A. Round the atomic mass. B. Subtract the atomic number from the rounded atomic mass. Check for Understanding • How many neutrons (o) does copper have? 64 - 29 _______ 29 35 35 Cu Copper neutrons 63.55 Check for understanding • Number of protons? 12 •Number of electrons? 12 •Number of neutrons? 12 24 -_________ 12 Mg magnesium 12 neutrons 24.30 On your paper WRITE A.P.E. • Atomic # = Proton # = Electron # M.A.N. • Atomic Mass – Atomic # = Neutron # Because… Atomic Mass = # of Protons + # of Neutrons