Download Chapter 3 - Blair Community Schools

Ch 3
Atoms and Moles
Atoms
Atomic theory: Democritus (400 BC)
atomos. Indivisible. All substances made of
atoms.
Experiments support laws:
Law of definite proportions:
Chemical compounds always contain the same
elements in exactly the same proportion by mass
Law of conservation of mass:
Mass can not be created or destroyed in ordinary
chemical and physical changes.
Law of multiple proportions:
Two elements combine to form two or more
compounds with a given mass of the other in
ratios of small whole numbers.
Daltons atomic theory
(1808)
Using atomic concepts & previous pg. Laws
1. All matter is composed of extremely small
particles called atoms
2. Atoms of a given element are identical in
their chemical and physical properties
3. Atoms of different elements differ in their
physical and chemical properties.
4. Atoms of different elements combine in
simple whole number ratios to from cpds.
5. In chemical reactions, atoms are combined,
separated or rearranged but never created,
destroyed or changed.
Revisions
#1 revised due to nuclear
reaction. #2 revised due to
isotopes.
Diatomic molecules H2, O2 etc.
Subatomic particles: proton,
neutrons and electrons.
Structure of the atom
Experiments to identify subatomic particles
Electrons:
JJ Thomson using cathode rays. Flow of particles
away from negative towards positive.
Plum pudding model
Charge of an electron -1.602 x 10-19 C
Mass of an electron 9.1 x 10-31 kg
+++
----------------anode
cathode
<-- flow
+ - +
- + +
+
Plum pudding
model
Structure of the atom
Rutherford
Gold leaf experiment
Alpha particles directed
towards gold foil
Results
Most past straight through,
some where deflected back
(1/20000)
Revised model:
Small dense positive charged
nucleus, volume defined by
locations of electrons, atom
mostly empty space
+
Nucleus
1/10000 the radius of the atom
Protons: positive charge and 2000
time the mass of an electrons
Neutral atom: # protons = #
electrons
Chadwick discovered neutron, no
charge, mass ~ proton, located in
nucleus.
Nucleus
Particle symbol charge/notation mass
Proton 1+1 p +1.6x10-19C/ +1 1.673x10-27kg
Neutron 10n
0/0
1.675x10-27kg
Protons in the nucleus repel (like charges) each
other
Neutrons are used to balance the repulsive
force to stabilize the nucleus,
Atomic number and mass
Atomic number:number
# of protons in the nucleus,
Same # for all atoms of the same element
Equal the # of electrons in a neutral atom.
Mass number:
Sum of the number of protons and neutrons of an
atom
Maybe different for isotopes of the same element.
Atomic structure/symbol. A = mass number,
Z = atomic number X = symbol of element
A
X
Z
1
H
1
2
H
1
3
H
1
Protium deuterium tritium
Isotopes
Atoms with same # of protons but different #
neutrons. Different mass #, same atomic
number.
Fill in the blanks:
Element symbol atomic # mass # #p #n

11 5
 oxygen
16

7
8
Electron configuration
Atomic models:
Rutherford: positive dense nucleus and
electron cloud.
Bohr: positive dense nucleus, electrons in
specific dist. and energies. Different energies
called quantum of energy.
Louis de Broglie: electrons move as waves
Constructive interference and diffraction patterns.
Electrons location in orbital (clouds) regions in an
atom where there is a high probability of finding
the electron.
Electrons and light
Light: move as waves that have given
frequencies, speeds and wavelength.
Speed( c)= 3.0 x 108m/s, constant
Wavelength (): distance between peaks,
meters
Frequency (): # waves per second, Hz or 1/s
c= as goes updoes down
Electromagnetic spectrum: range of energy,

High
E&
low E&
short 
long 
Gamma x-rays ultra violet visible infrared micro TV/radio
1pm, 1020 Hz
vibgyor
10km, 100kHz
Particle properties of electrons
Photoelectric effect:
Solar calculator
Minimum frequency to move electrons
Light emission:
Added energy to atom, electron moves from
grounded state to excited state (only certain
dist.)
Electron falls down to lower state and releases
energy of specific 
If in the visible light spectrum --> see color.
Grounded state: lowest energy state of a
quantized system
Excited state: state at which an atom's electron;
has more energy than the grounded state
Electron configuration
Describes to location (probable) of each
electron in an atom (grounded state)
using quantum numbers.
Quantum numbers/model
Specific properties of electrons in an atom
Electrons within an energy level are located
in orbital (regions of high probability of find
an electron)
Four quantum numbers to describe location
and properties of electrons
Principle quantum number (n):
4
quantum
numbers
Main energy level
Positive integer
As n increases so does distance from the nucleus
and energy of electron.
Angular momentum quantum number (l):
Sublevel of main energy level
Indicated the shape of the sublevel (pg 96, figure
21)
l = n-1
If n = 1 then l = 0, s orbital and spherical shape
If n = 2 then l = 1 or l = 0, l=1 p orbital peanut
shaped
If n = 3 then l = 2, l =1 or l = 0, l = 2 d orbital
double peanut shaped
 if n = 4 then l = 3, l = 2, l = 1 or l = 0, l = 3 f
orbital flower shaped.
Quantum numbers continue
Magnetic quantum numbers (m):
Indicate the number and orientation of orbital
around the nucleus.
If l = 0 the m = 0, one orbital (s)
If l = 1 then m = -1, 0, +1, three orbital (p)
If l = 2 then m = -2, -1, 0, +1, +2, five orbital (d)
If l = 3 then m = -3, -2, -1, 0, +1, +2, +3, seven
orbital (f)
Spin quantum number(ms)
+ 1/2
Indicates the orientation of am electron’s magnetic
field
2 electrons w/in an orbital have opposite spin to
balance their magnetic fields
Electron configuration
(short hand)
Location of each electron with in an atom
Rules:
Pauli exclusion principle: no two electrons in the
same atom will have the same 4 quantum numbers,
will always have opposite spin if in the same orbital.
Hund’s rule: atom in the grounded state, electrons
in a sublevel will fill each orbital before pairing up
Aufbau principle: electrons fill orbital from lowest
energy level to highest.
Use periodic table to determine order of fill
Orbital notation: all 4 quantum numbers listed.
Counting atoms
Atomic mass: mass of an atom expressed in
atomic mass units, amu (u)
Mass of p & n ~ 1 amu
Atomic weight: relative average of all the
isotopes of an element (g/mol)
Mole (n): SI unit used to measure the amount
of a substance. # of particles is the same as
the number of atoms in 12.00g of carbon-12
Molar mass: mass in grams of 1 mol of a
substance = to atomic weight of the element.
Avogadro's number: 6.02 x 1023, number of
atoms, ions, molecules or particles in 1 mole
1 mole = 6.02 x 1023
1 mole = molar mass.
Problems
Calculate the mass of 5.50 mol of
sodium.
How many moles of helium are
contained in 0.255g He?
How many moles are represented by
8.0 x 1013 atoms of Ca?
Calculate the mass of 4.89 x 1022 atoms
of Zn.
How many atoms are represented in
75.5g Ba?
Molar mass of cpds
Sum of all the atomic mass within a cpd
Example NaCl, BaSO4
Convert 3.91g NaCl to number of
particle NaCl
Convert 8.83 x 1024molecules CO2 to
mass CO2