Version A
Armando’s Copy
Chemistry 100: Summary of Chapters A & Q
These two chapters refine our knowledge of what atoms are and how they are made up. Unit A
deals with the discovery of subatomic particles and roughly how to organize the protons,
neutrons, and electrons. Unit Q shows us how the electrons are arranged in the atom – first with
the Bohr shells and then with the quantum mechanics model.
Compare this handout to the Key Terms and Concepts section at the end of the chapter.
UNIT A: DISCOVERY AND DEFINITION OF ATOMS & THEIR PARTICLES
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We covered this information to reenforce the ideas of discovery, explanation of phenomena,
and the importance of being flexible about our favorite theories – they can be changed!
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Important Topics
o Dalton’s Definitions (how many/which ones were shown to be wrong?)
o The 3 particles {protons, neutrons, electrons}, how heavy are they, what charge do they
have?
o Isotopes (Dalton’s Rule #_____ out the window). Don’t do math on page A.9. Know A,
Z, how to find number of each particle in an isotope from nuclear symbol.
o Atomic Mass (amu) – 1amu ~ 1 hydrogen’s mass.
o Periodic Table: organize elements, # of atoms per row = Bohr Shells. Known the names
of columns (also called families or groups). Also know features of the table: metals/nonmetals, transition elements.
o Memorization: Memorize 1st 3 rows of periodic table: element name, symbol, number.
Look at Figure A.8 – we’ll probably know most of these by using them all quarter.
Armando’s Copy
Version A
UNIT Q: ARRANGING ELECTRONS IN THE ATOM
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This chapter introduces the system that shows how electrons are arranged in the atom. This
system explains just about everything in chemistry – that’s why we tackle such a tough block
of information.
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Important Topics
o Light, Spectroscope: Don’t worry too much
about the deep details – but understand that the
thin colored lines from the Hydrogen lamp got
everything started.
o Bohr Model: Electrons orbit in shells with
different energies, 2 e- in 1st shell, 8 in 2nd &
3rd, 18 in 4th. Shell idea lasted into newer
theory.
Dark Violet
Violet
Blue/Aqua
Red
o Quantum Model:
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Very weird but it works!
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We now have 4 critera to identify electrons:
1. Principle Energy Level (n). Same as Bohr shell number.
2. Sublevel (s, p, d, or f). Shape of orbit.
3. Orbitals (x, y, z). Direction it points (up/down or left/right or front/back)
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Pauli Exclusion Principle. Electrons are like children – they won’t share unless they
have to. They are also lazy.
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Energy/Order of Orbitals. Use the triangle on pg Q.8, know the order. From
lowest energy to highest: n=1<2<3, s<p<d<f, Watch out: 3d<4s for some weird
reason.
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Electron Configuration. Shorthand like a chemical formula – so we don’t have to
draw the 3D picture all the time. (e.g. 1s2 means 2 electrons in the s sublevel of the 1st
shell (n=1), 3p5 means 5 electrons in the p sublevel of the 3rd shell (n=3). For an
atom of Nitrogen: 1s22s22p3 – add up the superscripts, 2+2+3=7, Z=7 for nitrogen.
Be able to write the electronic configuration for any atom!
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Valence Electrons. Electrons in the outer shell of an atom. We’ll use this a lot for
reactions and properties. Very simple to find: Locate the element on the periodic
table. Find its group number, that’s the number of valence electrons (Na: 1A, 1
valence electron. Cl: 7A, 7 valence electrons).
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Chemical Families. We’ll talk about these – be able to locate them on the periodic
table. Be able to draw the atom’s Lewis Dot.
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Lewis Dots. Another notation showing valence electrons for an atom. Put 1 dot for
each valence electron around the chemical symbol: Na, Mg:, :C: