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Atomic Structure Review
1. Models of the atom: hard indivisible sphere, solid sphere with positive and negative
uniformly distributed; nuclear atom; orbital atom; wave mechanical model
2. Using cathode ray tubes, the existence of electrons in atoms were discovered.
3. In the gold foil experiment, alpha particles(positive) bombarded gold foil. Most of the
particles went straight through. Conclusion: atom is mostly empty space. A few
particles bounced back. Conclusion: atom has a positive center/nucleus.
4. Today’s model: electrons are in orbitals – regions of high probability of finding an
electron – electron cloud model – a mathematical model – wave mechanical model.
5. Nucleus contains protons(positive) and neutrons(neutral/no charge). These are nucleons.
Nucleus contains almost all the mass.
6. Nuclear charge is positive – same as the number of protons.
7. Electrons are found in principal energy levels outside the nucleus. Maximum # of
electrons in the 1st four levels = 2,8,18,32
8. Protons have a mass of 1 amu and a charge of +1.
9. Neutrons have the same mass as a proton but no charge.
10. Electrons have a mass 1/1836 the mass of a proton and a –1 charge (“no” mass).
11. Atomic number = # of protons = nuclear charge.
12. Atomic mass of an element = protons + neutrons. Calculate # of neutrons.
13. Atomic mass unit is based on carbon having a mass of 12 amu.
1 amu = 1/12 the mass of a carbon-12.
14. Isotopes are two atoms of the same element that have the same number of protons but a
different number of neutrons. Therefore they have different masses.
15. Average atomic mass – weighted average of the naturally occurring isotopes.
16. Electron configurations are on the periodic table. Valence electrons are the electrons in
the outermost energy level of an atom in the ground state.
17. Valence electrons determine the chemical properties of an element.
18. Atom in its ground state - electrons are in their lowest energy level. This is the
configuration on the table.
19. Electrons become excited by absorbing energy and moving to a higher energy level.
20. The bright line spectrum is produced when an excited electron returns to the ground
state, releasing energy in the form of light.
21. Neutral atoms have the same number of protons and electrons.
22. A positive ion is formed when an atom loses one or more electrons.
23. A negative ion is formed when an atom gains one or more electrons.
24. Atoms become ions to attain a noble gas electron configuration. (a stable octet)
25. Unreacted atoms are always neutral. Ions are atoms that have reacted.
26. Stable octet means 8 valence electrons(or 2 if there is only one energy level.
27. You must be able to draw Lewis electron dot structures for atoms, ions, covalent and
ionic compounds.
28. Lewis electron dot structures are drawn showing valence electrons only.
Formula for calculating average atomic mass of one or more naturally occurring isotopes:
Ex.
Mass
Abundance
Isotope 1
23.67 amu
47.26%
Isotope 2
24.21 amu
0.87%
Isotope 3
22.73 amu
51.87%
(23.67)(47.26) + (24.21)(0.87) + (22.73)(51.87)
100