Chapter 3 Atoms & Moles
3-1 Substances Are Made of Atoms
Objectives: A. Familiarize yourself w/ the Law of Definite Proportions- Law of Conservation of Mass- Law of Multiple Proportions
Law of Definite Proportions- every molecule of a given
chemical compound always contains the same elements in the same proportions by mass
Law of Conservation of Mass- mass can not be created or destroyed in ordinary chemical reactions- reactants mass = products mass
Law of Multiple Proportions- when two elements combine to form different molecules, such as NO and NO2, they always combine in simple whole number ratios
B. Lists five principles of Atomic Theory (Dalton)
1. matter is composed of atoms which cannot be subdivided, created, or destroyed (not true today)
2. Atoms of a given element are identical in their physical and chemical properties (not true today)
3. Atoms of different elements differ in their physical and chemical properties 4. Atoms of different elements combine in simple whole number ratios to form compounds
5. In chemical reactions atoms are combined, separated, or rearranged but never created, destroyed, or changed
3-2 Structure of Atoms
Objectives: A. Describe the evidence for the existence of electrons, protons, and neutrons, and describe the properties of these subatomic particles.
Familiarize w/ the cathode ray tube experiment (J. J. Thompson)- discovery of electrons
Familiarize w/ gold foil experiment (Rutherford)- discovery of the nucleus and the atom was mostly empty space
B. Be able to find the number of electrons, protons, and neutrons in elements and define atomic number and mass number
Atomic number (number of protons)
Mass number (number of protons + neutrons)
C. Define isotope, and determine the number of particles in the nucleus of an isotope
Isotope – atoms of the same element that differ in the atomic mass thus the number of neutrons 11H (protium) 21H (deuterium) 31H (tritium)
D. Calculating average atomic mass (Refer to CH 7 page 234-235)
Avg. Atomic Mass = Mass of isotope (relative abundance) + Mass of isotope (relative abundance)
3-3 Electron Configuration
Objectives: A. Compare Rutherford’s and Bohr’s atomic models
Rutherford’s (planetary model- electrons in orbits)
Bohr’s- electrons travel around the nucleus in distinct energy levels
Electron Cloud- electrons travel around the nucleus in waves or regions called orbitals
Skip pgs 92-94
Ground state- electrons in their lowest energy
Excited state- electrons gain energy a jump to higher energy levels, but return releasing energy in the form of light (color unique to the element)
B. Lists the four quantum numbers and describe their significance
n principle quantum number ( main energy levels) n = 1-7
2n2 (equals the number of electrons on a given level)
l angular momentum quantum number (sublevels) (shape of the electron cloud)
The number of sublevels on a given level is equal to the level (level 1 has 1 sublevel and level 4 has 4 sublevels)
The sublevels are named s, p, d, f, g etc , thus the second level has two sublevels named s and p
s = 0, p = 1, d = 2, f = 3 etc
s is spherical in shape, p is peanut shape, d is double peanut shape, f is flower
m magnetic quantum number–orbitals (direction in space of the electron clouds) The number of orbitals within a given level is equal to n2
- (0) - - - (-1,0,1) - - - - -(-2,-1,0,1,2) ------(-3,-2,-1,0,1,2,3,)
s p d f
s has 1 orbital p has 3 d has 5 f has 7
s spin quantum number(spin clockwise or counterclockwise) +1/2, -1/2 a single orbital can only occupy 2 electrons that must have opposite spins
C. Writeelectron configuration and know Pauli exclusion principle and aufbau principle Pauli exclusion principle- no two electrons can have the exact same set of 4 quantum numbers (they can only have 3 in common)
Aufbau principle- electrons must occupy the lower energy levels before moving to higher energy levels
Hund’s Rule- electrons must be added singly to an orbital before pairing them up and when adding them singly, they must have the same spin
Diagonal Rule 1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
Electron configuration
Orbital filling diagram
Short hand electron configuration
3-4 Counting Atoms
Objectives: A. Atomic mass vs molar mass
Atomic mass is the mass of one atom in amu (atomic mass units)
Molecular mass is the mass of one molecule (nonmetals) in amu
Formula mass is the mass of one formula unit (metal w/ nonmetal) in
amu
Molar mass is the atomic, molecular, formula mass not in amu, but in grams (mass of one mole of a substance)
B. Define mole
Mole (expresses an amount) is the number of atoms in 12 grams of carbon (just like a dozen expresses 12 of something)
Avogadro’s number = 6.023 x 1023 particles = 1 mole
C. Calculate simple mole problems
1 mole = 6.023 x 1023 particles
1 mole = molar mass
Mass (grams)
↕ molar mass
Mole
↨ 6.023 x 1023
Molecules
Formula Units
↨ # of
Atoms and Ions
)