Bellringer (Page 24): What does this represent?

AtomsPage 23 of your notebook

Objectives

Summarize the observed properties of cathode rays that led to the discovery of the electron.

Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus.

List the properties of protons, neutrons and electrons.

Define atom and isotope.

Atoms

Very small 1 x 1022 atoms in 1

penny Equivalent to 1

grain of sand in a sandbox the size of Texas

Properties of Atoms

Smallest characteristic of a given element

Make up everything Different for each element

Only 90 elements occur in nature

Atoms

Too small to see with an ordinary microscope

Need scanning tunneling microscope to get an image of an atom Tells nothing about

the structure of an atom

Atoms

Atoms in Kanji, they spell "atom" using iron atoms on a copper surface. The literal translation is something like "original child."

Ancient Greeks Theory

Only 4 elements Fire (red) Water (blue) Air (grey) Earth (brown)

Ancient Greeks and the Atom Democritus

postulated tiny particles of water that could not be subdivided further Called them atomos

(means indivisible)

Aristotle

Thought everything was continuous

Atoms didn’t exist Ancient Greeks

could not test either model

This view prevailed for >2000 years

Foundations of Atomic Theory

By the 1790’s, the study of matter was revolutionized by the analysis of chemical reactions Beginning of technology

This lead to the discovery of several basic laws

Father of Modern Chemistry

law of conservation of matter (mass):

The total mass of substances does not change during a chemical reaction.

reactant 1 + reactant 2

total mass

product

total mass=

iron + oxygen iron(III) oxide

Fe + O2 Fe2O3

70.0 g + 30.0 g 100.0 g

100.0 g

Antoine Lavoisier (1743-1794)

Lavoisier Accurately weighed starting

materials and products of reactions

Law of Conservation of Mass

Mass is neither created nor destroyed during chemical reactions

Cannot create material out of thin air Make new materials by rearranging

atoms Basis for chemical calculations

1. All matter is composed of extremely small particles

Atoms are indivisible2. Atoms of a given element

are alike but different from atoms of any other element

Atoms for any element have identical chemical and physical properties

1803 John Dalton:

3. Atoms can not be subdivided, created or destroyed.

4. Compounds are formed when different elements combine in fixed proportions

▪ Typically written with smallest whole numbers - Law of Definite Proportions - Law of Multiple Proportions

1803 John Dalton:

5. A chemical reaction involves combining, separating or rearranging of atoms

• Law of Conservation of Mass

1803 John Dalton:

Modern Atomic Theory

Modern Atomic Theory proved a few of Daltons ideas where wrong. Atoms are divisible into smaller particles▪ Electrons, neutrons and protons

A given element can have atoms with different masses▪ Isotopes

The Discovery of Atomic Structure

Cathode rays – The ray of light emitted by the cathode (negative electrode) in a glass discharge tube; travels in straight lines, unless deflected by magnetic or electric fields.

Studied cathode rays and determined that

J. J. Thomson (1897)

Atoms are divisible into even smaller

particles.

Millikan’s Oil-Drop Experiment

Determined the negative charge of an electron

James Chadwick

• Discovered a particle in the nucleus that had no charge•neutron

Roentgen

Studied the glow caused by the cathode ray tube

Chemically treated paper that glowed▪ Even through

walls!

Discovery of RadioactivityBecquerel

found that uranium ores would fog photographic plates in the dark

Marie and Pierre Curie Marie and Pierre

Curie isolated 1/30 ounce ofradium from one ton ofuranium ore.

Marie died fromradiation-inducedleukemia.

The pages of her labnotebook were laterfound to becontaminated withradioactivefingerprints.

Radioactivity

– spontaneous emission of radiation from certain unstable elements

Behavior of Radioactivity

Rutherford’s Experiment

The Discovery of Atomic Structure

Rutherford’s a-Scattering Experiment (Gold Foil) and Discovery of the Atomic Nucleus

The vast majority of an atom’s volume is empty space.

Nucleus - The tiny central region of the atom that contains the positive charge and essentially all the mass.

Structure of Atom

Rutherford suggested: Most of mass in nucleus All the positive charge

Nucleus: protons and neutrons Neutrons have mass but

no charge Very small size compared

to the rest of the atom The rest of the atom

contains the electrons

Subatomic Particles

Particles smaller than the atom Number of protons in element = atomic

number Element: all atoms having the same

atomic number

Atomic Structure

Isotopes Atoms having the same atomic

number BUT differing in number of

neutrons

Symbols for Isotopes

ZAX

A = mass number = number of protons + number of neutrons = number of nucleonsZ = atomic numberX – symbol of the element

Isotopes of hydrogen

A Neutron walked into a bar and asked how much for a drink. The bartender replied, “for you…. no charge.”

-Jaime- Internet Chemistry Jokes