Download Chapter 3 Study Guide

Chapter 3 Study Guide
Section 1:
1) Idea of the atom has been around for a long time- since Democritus in 430 BC.
a. Believed the atom was the smallest unit of matter- just a blob.
2) Three laws: conservation of mass, definite proportions, and multiple proportions.
a. Know what each law states and be able to identify laws from examples.
ie: The ratio by mass of H to O in water is always 1:8. This demonstrates the
law of definite proportions because the ratio of H to O is constant.
3) Dalton’s atomic theory
a. Used the ideas of others.
b. Know which principles are no longer true today and why.
Section 2:
1) Discovery of subatomic particles and atomic model theories (be able to recognize names of
scientists).
a. Thomson- discovered the electron by experimenting with cathode ray tubes.
i. Used a magnet to determine the charge on the beam inside the tube.
ii. Proposed the ‘plum pudding’ model (see notes for picture and description)
of the atom.
b. Rutherford- discovered the positively charged proton in the nucleus.
i. Performed the ‘gold foil’ experiment- shot positively charged beam (alpha
particles) at a piece of gold foil.
ii. Most of the particles went through the foil (atom is mostly empty space), but
a few were deflected (hit the positively charged nucleus).
iii. Proposed the ‘planetary’ model of the atom (see notes for picture and
description).
c. Chadwick- credited with discovering the neutron.
2) Neutrons are important because they help hold the protons together in the nucleus.
3) Electrons have the smallest mass, compared to the protons and neutrons.
4) Be able to determine the numbers of e-, p+, and n in an atom.
a. Atomic number = # p+ (also = #e- in a neutral atom)
b. Mass number = #p+ + #n
c. Ions- atoms with a charge.
i. Positive charge- electrons lost; subtract electrons.
ii. Negative charge- electrons gained; add electrons.
d. Know what isotopes are- atoms of the same element with different numbers of
neutrons- and the methods used to designate isotopes of atoms:
i. carbon-12 and carbon-14
ii.
12
6
C and
14
6
C
(name of element – mass #)
(nuclear symbol method)
Section 3:
1) Bohr model of the atom.
a. Explained why electrons don’t crash into the nucleus.
b. Electrons can only exist at certain energy levels around the nucleus.
2) Electrons act as both particles and waves.
3) Quantum model of the atom is the model accepted today; has orbitals where you are likely
to find e- (based on probability).
i. Called electron clouds because these regions appear fuzzy; no distinct
boundaries.
ii. Orbitals are different from orbits! Orbits are specified paths around an object.
Orbitals are regions of high probability where electrons are found.
4) Light acts as both waves and particles- Einstein studied this in the photoelectric effect.
5) Excitation of electrons and light energy:
a. Atoms in their ordinary state have electrons in the ground state (low energy).
b. Electrons can be excited to a higher energy level (absorb energy).
i. Don’t like to be at high energy, so they relax back down.
c. When electrons relax back down to lower energy levels they can release energy as
light, which you see as different colors.
6) Quantum Numbers.
a. Like the address of an electron- tells you where electrons are located.
i. n = principal quantum number (energy level)
ii. l = angular momentum quantum number (shape)

s shape = sphere

p shape = figure 8/peanut

d shape = four leaf clover

f shape (don’t need to know what this looks like)
iii. m = magnetic quantum number (orientation of orbital)

Number of orientations per shape: s=1, p=3, d=5, f=7
iv. s = spin quantum number (spin/orientation of electron)

s = +½ or – ½ ; up or down arrow; clockwise or counter-clockwise
7) Electron Configurations
a. Use the periodic table- look at row numbers and blocks.
i. Tells you the order in which electrons fill up an atom.
b. Rules to obey when determining electron configurations:
i. Pauli Exclusion Principle: no two electrons in the same orbital can have the
same 4 quantum numbers.
ii. aufbau principle: electrons fill up the lowest available energy levels first.
iii. Hund’s Rule: one electron must occupy each orbital before pairing.
c. Know the types of electron configurations and how to determine them!
i. Full
ii. Abbreviated
iii. Orbital Diagram (may be full or abbreviated- this uses arrows and horizontal
lines).
Section 4:
1) Atomic mass unit (amu): used for the very small masses of atoms (1amu = 1 Dalton).
2) Mole: Represents a certain quantity/amount of substance (just like 1 dozen = 12).
a. Molar mass: mass in grams of one mole of a substance.
i. Used to convert between mass (g) and moles.
ii. Units: g/mol
3) Avogadro’s Number
a. 1 mole = 6.022x1023 particles, atoms, molecules, etc.
b. Used to convert between the number of something (atoms, ions, molecules, formula
units) and moles.
4) You must use and know dimensional analysis when performing calculations!
a. Convert between moles and particles
b. Convert between moles and grams
c. Convert between grams and particles
*Bolded words are vocabulary that you should know!