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