DOR: Test Survey
1) How much time did you spend outside of class in preparation for Test I ?
1) What materials did you use to study for the test?
1) Was the test material represented through the study guide and class
materials?
1) What grade do you feel you deserve on the test?
The Atom
Law of Conservation of
Mass/Matter
 Matter cannot be created or
destroyed
 Total mass is constant in chemical
reactions.
 Originated with Antoine Lavoister
(1700s)
 Quantitative mass data of
reactants and products in
mercury oxide decomposition.
Law of Definite Proportions
 Proposed by Joseph Proust (late 1700s)
 Decompositions and research with copper
carbonate
 Compound composition and properties are fixed
 All compound samples have the same
composition
 Same % of elements in the compound
 Ex. H2O
Law of Multiple Proportions
 2+ compounds with same 2 elements
 Compositions of these compounds are related
 Masses of elements related to each other in whole
number ratios
 Proposed by John Dalton in addition to his atomic
theory.
 Ex. CO2 (2:1), CO (1:1)
Terminology
 Element– basic unit of a substance, contain
only ONE type of atom, represented by
symbol.
Example: Ag, only contains Ag atoms.
 Atom—smallest particle of an element that
still contains element properties.
 Example: One atom of Au, cannot have a smaller particle
of gold and still be gold.
Compound vs. Molecule
 Compounds:
 more than one element
 elements combined in definite
proportions
 Molecule:
 Smallest unit of a compound that still
retains the properties of the compound.
How far back does the
“atom” go?
 Democritus
 400 B.C.
 Called the basic unit of
matter an “atom”
The Atom and its Structure
Dalton Atomic Theory
 1800s
 Atoms make up
elements.
 Atoms form
compounds as a whole
and cannot be divided.
Compounds formed
from atoms joining in
FIXED proportions
Dalton Atomic Theory
(cont.)
 All matter made of
atoms
 Atoms of an element
have the same size,
mass, etc.
 Different atoms have
various sizes, mass,
etc.
 Atoms cannot be
divided, destroyed, or
created.
 Atoms rearrange in
chemical reactions.
John Thomson
 1897
 Cathode-Ray experiments.
 Discovered the electron
particle and its possible
charge (-).
 Determined ratio between
mass and charge of an
electron
Robert Millikan
 1909, American
 Oil drop
experiments.
 Found the mass of an electron
(VERY small) with
Thompson’s data
 Currently, mass of electron =
9.109 x 10-31kg
 Discovered electron charge
 e = -1.602 x 10-19 C
Early Models of the Atom
Thompson
 Must be a balance between negative and positive
charges
 “Raisin-Pudding” model
 Uniform distribution of positive charge
 Positive cloud with stationary electrons
Early Models of the Atom
Rutherford
 How are electrons distributed in an atom?
 Discovered alpha particles as 42He
 Experiments with Au, Ag, and Pt foils
bombarded with alpha particles
Early Models of the Atom
Rutherford
 Mostly empty space
 Small, positive nucleus
 Contained protons
 Negative electrons
scattered around the
outside
James Chadwick
 1932 discovered neutrons contained
in atom’s nucleus
 No charge
 Mass approximately same as
proton mass
Early Models of the Atom
Bohr
 1913—hydrogen atom structure
 Physics + quantum theory
 Electrons move in definite
orbits around the positively
charged nucleus—planetary
model
 Does not apply as atoms
increase in electron number
Erwin Schrödinger
 Quantum mechanics
 1926---wave equation
 Electrons behave more like
waves than particles
Heisenberg’s Uncertainty
Principle
 Electron’s location and direction cannot
be known simultaneously
 Electron as cloud of negative charge
Modern Model of the Atom
The electron cloud
 Sometimes called the
wave model
 Electron as cloud of
negative charge
 Spherical cloud of varying
density
 Varying density shows
where an electron is more
or less likely to be
How did we discover electron
arrangement in an atom?
ELECTROMAGNETIC
RADIATION ! ! !
Waves
 Repeated disturbance through a medium (air, liquid) from
origin to distant points.
 Medium does not move
 Ex. Ocean waves, sound waves
Characteristics of Waves
 Wavelength
 Distance between 2 points within a wave cycle
 2 peaks
 Frequency
 # of wave cycles passing a point for a particular time unit
 Usually seconds.
Wavelength and frequency are
inversely proportional.
Electromagnetic Waves
 Produced from electric charge movement
 Changes within electric and magnetic fields carried over a
distance
 No medium needed
Electromagnetic Spectrum
 Contains full range of wavelengths and frequencies found
with electromagnetic radiation
 Mostly invisible, visible range (390 nnm -760 nm)
 Different materials absorb/transmit the spectrum
differently.
Types of Spectra
 What is a spectra?
 Spectrum– white light/radiation split into different wavelengths and
frequencies by a prism
 Continuous spectrum
 No breaks in spectrum
 Colors together
 Line spectrum
 Line pattern emitted by light from excited atoms of a particular element
 Aided in determining atomic structure
Line Spectrum
 Pattern emitted by light from excited atoms of an element
 Specific for each element
 Used for element identification
Flame Tests
 Some atoms of elements produce visible light if heated
 Each element has a specific flame color
 Examples: Li, Na, Cs, Ca
A Bit of Quantum
Theory……
Max Planck
 1900
 Related energy and radiation
 Quantum---smallest amount of energy
 Atoms can only absorb/emit specific quanta
Albert Einstein
 1905
 Added to Planck’s concept
 Photons—
 Bundles of light energy
 Same energy as quantum
 Photons release energy and electrons gain energy
 Threshold frequency– minimum amount of energy needed by photon to
extract electron
THEREFORE ………
 Light is in the form of electromagnetic waves
 Photons can resemble particles
 Gave raise to the possibility of thinking about wave AND
particle qualities of subatomic particles (electron)
Atomic Structure
Nucleus
 Protons
 Neutrons
Electrons
Atomic Structure
 Electrons
 Tiny, very light particles
 Have a negative electrical charge (-)
 Move around the outside of the nucleus
Atomic Structure
 Protons
 Much larger and heavier than electrons
 Protons have a positive charge (+)
 Located in the nucleus of the atom
Atomic Structure
 Neutrons
 Large and heavy like protons
 Neutrons have no electrical charge
 Located in the nucleus of the atom
Atomic Structure
Describing Atoms
Atomic Number = number of
protons
In a neutral atom, the # of protons
= the # of electrons
Atomic Mass= the number of
protons + the number of neutrons
Isotopes
 The number of protons for a given atom never changes.
 The number of neutrons can change.
 Two atoms with different numbers of neutrons are called
isotopes
 Isotopes have the same atomic #
 Isotopes have different atomic Mass #’s
Isotopes
Ions
 An atom that carries an electrical charge is called an ion
 If the atom loses electrons, the atom becomes positively charged.
 If the atom gains electrons, the atom becomes negatively charged
Ions
 The number of protons does not change in an ion.
 The number of neutrons does not change in an ion.
 So, both the atomic number and the atomic mass remain
the same.
PEN Method for-- H
O
P
 He
F
S
 Li +1
Ne
Cl -1
 Be
Na
Ar
 U-238
Mg +2
K