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Unit 3: Atomic Structure

Unit 3: Atomic Structure. Atomic Number, Mass Number, and Isotopes. After today, you will be able to…. Find the atomic mass, atomic number, and symbols of elements off of the Periodic Table Calculate the number of neutrons in a particular atom Explain what an isotope is. Atomic Number.

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Unit 3: Atomic Structure

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  1. Unit 3: Atomic Structure Atomic Number, Mass Number, and Isotopes

  2. After today, you will be able to… • Find the atomic mass, atomic number, and symbols of elements off of the Periodic Table • Calculate the number of neutrons in a particular atom • Explain what an isotope is

  3. Atomic Number • The number of protons in the element. • Always a whole number • Example: Oxygen’s atomic number is8, so there are 8protons in Oxygen’s nucleus

  4. Atomic Number • For neutral elements (no charge) the # of p+ = # of e- • The number of protons willnever change for an element • It is like our social security number, it identifies them.

  5. Atomic Mass • Read right off the Periodic Table. • The number will have a decimal. • It is the average (weighted)of all the elements isotopes.

  6. 8 O Oxygen 15.999 Atomic Number vs. Atomic Mass Atomic number Atomic mass

  7. Mass Number • Number of protons & neutrons combined • Always a whole number

  8. Finding the Number of Neutrons • Neutrons = mass # - atomic # • Example: Oxygen’s mass number is 16 and its atomic number is8. The number of neutrons will be 16-8 = 8.

  9. Isotopes • Atoms with the same number of protons, but different number of neutrons. • They are chemically alike • Have different mass numbers • Written like this: • Element–Mass Number

  10. Examples: Neutral hydrogen isotopes Hydrogen-1 Hydrogen-2 Hydrogen-3 1 proton 1 proton 1 proton 1 electron 1 electron 1 electron 0 neutrons 1 neutron 2 neutrons

  11. Summary • Atomic # = protons = electrons (neutral atoms) • Mass # = protons + neutrons = rounded atomic mass • Neutrons = mass # - atomic #

  12. Practice makes perfect…  16 32 16 16 N 7 7 7 Cl 35 17 Ca 20 20 20

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