Atomic TimelineWARM-UP: Take out your Ch. 3 VOCABULARY and timeline materials and

begin completing timeline.

• With your table, you are to create an Atomic Discovery Timeline/Historical Collage that includes the following:

• Democritus• Aristotle• Law of Conservation of Mass• Law of Definite Proportions• Law of Multiple Proportions• John Dalton• Joseph Thompson• Robert Millikan• Ernest Rutherford

•Each person or discovery should be on one piece of paper and include a summary, date, and illustration

• NO NO2• N:O N:O• 1:1 1:2 (8.5 x 2)= 1.71.7g :1 g 1.7g : 2g

Compound Mass of nitrogen that combines with 1 g oxygen

NO 1.70

NO2 0.85

NO4 0.44

NO2 NO4 N:O N:O 1:2 1:4(2x.85) =1.7 (.44 x 4) =1.761.7 g : 2 g 1.76 to 4 g

Compound Mass of nitrogen that combines with 1 g oxygen

NO 1.70

NO2 0.85

NO4 0.44

August 23WARM UP: Find the ratio of N :O

4NO

NO

Compound Mass of nitrogen that combines with 1 g oxygen

NO 1.70

NO2 0.85

NO4 0.44

NO NO4N:O N:O

The Atom

History and Structure

Atomic Discovery and Structure

The Atom

Atom

An atom is the smallest particle of an element that retains the chemical properties of that element

The nucleus is a very small region located at the center of an atom

The nucleus is made up of at least one positively charged particle called a proton and usually one or more neutral particles called neutrons

The Atom

Atom

Surrounding the nucleus is a region occupied by negatively charged particles called electrons

Protons, neutrons, and electrons are often referred to as subatomic particles

The Atom

The Atom

• Discovery of the Electron

• Cathode Rays and Electrons

» Experiments in the late 1800s showed that cathode rays were composed of negatively charged particles

» These particles were named electrons

The AtomJoseph John Thomson’s (1987) cathode-ray tube experiments measured the charge-to-mass ratio of an electron

The Atom• Charge and Mass of the Electron

• Robert A. Millikan’s (1909) oil drop experiment measured the charge of an electron

• With this information, scientists were able to determine the mass of an electron

Atomic Discoveries: Experiments

• file:///D:/student/ch03/sec02/vc02/hc603_02_v02fs.htm

Discovery of the Atomic Nucleus• More detail of the atom’s structure was provided in

1911 by Ernest Rutherford and his associates

• The results of their gold foil experiment led to the discovery of a very densely packed bundle of matter with a positive electric charge

• Rutherford called this positive bundle of matter the nucleus

Atomic Discoveries: Experiments

• file:///D:/student/ch03/sec02/vc02/hc603_02_v02fs.htm

The Atom

• Composition of the Atomic Nucleus

• All atomic nuclei are made of protons and neutrons

• A proton has a positive charge equal in magnitude to the negative charge of an electron

• Atoms are electrically neutral because they contain equal numbers of protons and electrons

• A neutron is electrically neutral

Composition of the Atomic Nucleus

• The nuclei of atoms of different elements differ in their number of protons and therefore in the amount of positive charge they possess

• Thus, the number of protons determines that atom’s identity

Size of the Atom

The radius of an atom is the distance from the center of the nucleus to the outer portion of its electron cloud

Because atomic radii are so small, they are expressed using a unit that is more convenient for the sizes of atoms

This unit is the picometer, pm (10 -12)

Atomic Timeline

• With your table, you are to create an Atomic Discovery Timeline/Historical Collage that includes the following:

• Democritus• Aristotle• Law of Conservation of Mass• Law of Definite Proportions• Law of Multiple Proportions• John Dalton• Joseph Thompson• Robert Millikan• Ernest Rutherford

•Each person or discovery should be on one piece of paper and include a summary, date, and illustration