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DOR Chemical/Physical
Changes Classify each change as either chemical or
physical.
1) Gasoline in your engine burns as you start the car.
2) Distilled water
3) Rust on a nail
4) Glow sticks
5) Medicine crushed into a powder
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, one element masses combined with second element’s mass in whole number ratio.
Compositions of these compounds are related
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.
Stated electrons have a negative charge
Determined ratio between mass and charge of an electron
Robert Millikan
1909, American
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
Oil drop experiments.
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
SOOO we have protons and electrons…anything else?
Experiments shooting alpha particles at Beryllium atoms
Colleague of Rutherford
Participated in Manhattan Project
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
Homework
Read pp. 36-39, 263-267, 276-280
DOR: Atomic Theory 9/4
1) Which scientist is credited with the Law of Conservation of Mass?
2) This scientist performed cathode ray experiments to determine the ratio between the mass and charge of an electron.
3) This scientist found the actual mass and charge of an electron following up on another scientist’s data.
4) An electron’s location and direction cannot be simultaneously known. This statements is from _______________________________________
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.
c = νλ
c = speed of light, 3.0 x 10 8 m/s
ν= frequency (s-1)
λ= wavelength (nm)
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
E = hν h= 6.626 x 10 -34 Js (Planck’s constant)
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
E = hν (energy of photon)
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)
Example 1 Calculate the energy found in a photon of red light with a wavelength of 700.0 nm
Example 2 How much energy (in joules) is found in the radiation of the hydrogen atom emission spectrum with a 656.3 nm wavelength?
Homework 9/4/13
Read over Law of Conservation of Mass lab procedure.
Read pp. 267-274
Problems p. 293 #31
Problems p. 294 #37, 38, 41, 42
DOR: Test Survey
1) How much time did you spend outside of class in preparation for Test I ?
2) What materials did you use to study for the test?
3) Was the test material represented through the study guide and class materials?
4) What grade do you feel you deserve on the test?
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.
Ex. 1: Ca
Ex. 2: H+1
Ex. 3: Bi-212
PEN Method for---
O -2 P
F S-2
Li +1 Cl
Ba +2 Na
Mg Po-215
C -14 Al+3
N Ra-226
U-235 U-238