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Unit 3
Language of Chemistry
Part 1
Zumdahl: Chapter 4
Holt: Chapter 3
ATOMS: The Building
Blocks of Matter
Objectives
1.
2.
3.
4.
5.
Law of conservation of mass
Law of definite proportions
Law of multiple proportions
Dalton’s Atomic Theory
How Dalton’s Atomic Theory relates to 1,
2, & 3
Atomic Theory Foundations
Law of Conservation of Mass – mass is
neither created or destroyed during a
chemical or physical change
Law of Definite Proportions – a compound
contains the same proportions by mass
regardless of the size of the sample
Example:
NaCl – always 39.34% Na & 60.66% Cl
Atomic Theory Foundations
Law of Multiple Proportions – if two or more
different compounds are composed of the
same two elements, then the ratio of the
masses of the second element combined
with a certain mass of the first element is
always a ratio of small whole numbers
Example
CO2 and CO : ratio of oxygen is always 2:1
JJ Thomson
Showed atoms could emit negative particles
“plum pudding” model
Electrons were embedded in a positively
charged spherical cloud
Rutherford
• Shoots alpha particles (Helium atoms) at
gold foil
• Expected to pass right through
• Particles are deflected
• Leads to idea of a dense positively
charged center with e- orbiting around it
Ernest Rutherford
• Gold foil experiment
Dalton’s Atomic theory
1. All matter is composed of atoms
2. Atoms of an element have the same size,
mass and properties; atoms of a different
element have different sizes, masses and
properties
3. Atoms cannot be divided, created or destroyed
4. Atoms of different elements combine in simple
whole number ratios
5. Chemical reactions combine, separate, or
rearrange atoms
Modern Atomic Theory
• Atoms can be divided
• Atoms of the same element can have
different masses
• All else remains the same
Structure of the Atom
Objectives
Discovery of the Electron
Rutherford’s Experiments
Protons, Neutrons, Electrons
Atomic Structure
• Electron = no mass; negative charge
• Proton mass = hydrogen atom; positive
• Neutron mass = hydrogen atom; no charge
• Dalton’s Model
• JJ Thompson’s Plum Pudding Model
The Electron
• Mass of 9.109 x 10
-31
• Negative charge
kg
The Proton
• Mass = 1.673 x 10
-27
• Positive charge
kg
The Neutron
• Mass = 1.675 x 10
-27
• No charge
kg
Comparing Theories
Dalton
See notes
Thompson
Plum pudding
model
Rutherford
Concept of the
nucleus
Electrons
scattered thru
positively
charged cloud
Positively
charged
Solid sphere
Counting Atoms
Objectives
Explain isotopes
Define atomic number, atomic mass
Determine number of protons, neutrons & electrons
Define mole and molar mass
Convert between grams, moles, and atoms
Atomic Number
• Atomic Number
– # of protons in nucleus
• Element Symbol
• Element Name
• Atomic Weight
• Electron
Configuration
3
Li
Lithium
6.941
[He]2s
1
Isotopes
Def: atoms of the same element that have
different masses
Example: hydrogen
protium – 1 proton in nucleus
deuterium – 1 proton; 1 neutron
tritium – 1 proton; 2 neutrons
*Nuclide – general term for any isotope
Writing Isotopes
mass number Element Symbol
atomic number
Example – Uranium 235
235
92
U
Mass Number
Def: the number of protons and neutrons in
the nucleus of an isotope
mass # - atomic # = # of neutrons
Example – oxygen
Mass # (16) – atomic # (8) = # of neutrons (8)
Average Mass Number
Def: the weighted average of the atomic
masses of the naturally occurring isotopes
of an element
Like calculating a “weighted” grade
(decimal % of each isotope x mass of that
isotope)
Sample Calculation
Isotope
oxygen - 16
oxygen - 17
% abundance
99.762
0.038
Atomic Mass
15.994915
16.999131
oxygen - 18
0.200
17.999160
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