1. Chapter 3 “Atomic Structure”

2. Definition of an Atom Dictionary definition The smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element. Origin of word atom: Greek word “atomos” which means uncuttable, or indivisible, something that cannot be divided further.

3. Parts of the Atom

4. PartSymbolCharge Mass Number Mass in amu Proton p+p+ + 11~ 1 amu Neutron nono 01~ 1 amu Electron e-e- - 10~ 0 amu An electron weighs 1/1836 of a proton

5. What Does an Atom Look Like? - Let’s look at the Helium atom

6. Helium Atom

7. How small is an atom? 0.22 nanometers 0.00000000022 meters

8. What Makes Atoms Different From Each Other? The number of PROTONS!!! The atomic number (Z) equals the number of proton’s in an element’s atom. Since elements on the periodic table are neutral (no charge), we can assume the # of electrons = # of protons. The mass number equals the total number of protons and neutrons in the nucleus of an atom.

9. How Many Neutrons? If we know the mass number then we can figure out how many neutrons are present by the following equation: mass # - atomic # = # of neutrons Q: How do we figure out what the mass number is??? A: Round the atomic mass on the periodic table to the nearest whole number The mass number equals the total number of protons and neutrons in the nucleus of an atom.

10. Nuclides The particles that make up the nucleus of an atom are called nuclides. The nuclide shows the mass number along with the atomic number (# of protons) of an atom. # protons # neutrons # electrons 2 2 2 # protons # neutrons # electrons # protons # neutrons # electrons 22 26 22 3 3 4

11. What the Quark? Turns out protons and neutrons are made from smaller parts!! Uggh! Quarks

12. Same Element Different Atom All atoms of a particular element are not exactly alike. Some elements have atoms with different masses (isotopes)

13. Cool Down What are two things you learned today? What do you still not understand? Homework due Wednesday Worksheets 4.1 and 4.2