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• Chapter 2: Learning Objectives• Explain the ancient Greeks ideas about the characteristics of matter.

• Describe the significance of the Laws of Conservation of Mass and Definite Proportions.

• Calculate the amounts of elements from the composition of a compound.

• Explain why the idea that matter is made of atoms is a theory.

• Understand how atomic theory explains the Law of Conservation of Mass.

• Describe how the elements are arranged in the periodic table and why the arrangement is important.

• Distinguish atoms from molecules.

• Identify elements that could be classified as hazardous or rare.

• Explain how green chemistry can change technologies that rely on hazardous or rare elements.

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Atoms: The Greek Idea

~384 B.C.E., Aristotle:

All matter is composed of four elements and all matter is continuous, not atomistic.

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The Tenets of Aristotle’s Model of Matter• The Aristotle atomic theory disagreed with the

prevailing theories of the time.

• He was not able to see how atoms could stay in perpetual motion in a void.

• He developed a theory that was based on the four elements. Aristotle’s theory made a great generalization off all matter being made of the four elements: fire, water, earth, and air.

• He also believed that there were four qualities to these elements: dryness, hotness, coldness, and moistness.

• Based on these beliefs fire would hold the characteristics of being dry and hot, water is wet and cold, air is hot and wet, while the earth is dry and cold.

• In the Aristotle model there were two forces: conflict and harmony. So, each of the elements move naturally in a line to their “proper place,” where it will be at rest. Therefore, conflict was thought to cause bad things, and harmony good things.

• Superior and in ways ruling these other elements, Aristotle believed was a fifth element called aither which solely comprised the heavens.

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~ 450 B.C.E., Leucippus and Democritus

Atomos: The point at which matter can no longer be subdivided.

Atoms: The Greek Idea

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Leucippus & Democritus’ Atomic Model• Matter is physically made up of

atoms.

• Atoms are always moving.

• Atoms are invisible.

• Atoms are homogenous and atoms are solid.

• Atoms are indivisible & cannot be created or destroyed or changed.

• Atoms differ in size, shape, weight position and arrangement.

• There are spaces between atoms. The more empty space the heavier the atom gets.

• For example: Oil is made up of smooth solid atoms that can easily pass each other. Liquid has large round atoms and solids are made with pointy small solid atoms.

• L&M’s atomic model was simply a round sphere with no electrons, protons, or neutrons. 

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Early 1700s Lavoisier

Law of Conservation of Mass: During a chemical change, matter is neither created nor destroyed.

Great Vid….http://www.youtube.com/watch?v=x9iZq3ZxbO8&feature=related

Lavoisier: The Law of Conservation of Mass

Mon Cheri, now about the combining ratios of the gasses….

Oh Antoine-Lauren I love it when you speak of dephlogistated air.

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Lavoisier: The Law of Conservation of Mass

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1799, Proust

Law of Definite Proportions:

A compound always contains the same elements in certain definite proportions.

Uhh…what is a compound?

Proust: The Law of Definite Proportions

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• Regardless of the source, copper II sulfate always has the same composition of it’s constituent elements.

• What elements are in this substance? …compound?

Proust: The Law of Definite Proportions

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The Berzelius experiment illustrates the Law of Definite Proportions.

Proust: The Law of Definite Proportions

CONCEPTUAL EXAMPLE 2.1 Mass Ratios

Solution

Exercise 2.1A

Exercise 2.1B

Hydrogen gas for fuel cells can be made by decomposing methane (CH4), the main component of natural gas. The decomposition gives carbon (C) and hydrogen (H) in a ratio of 3.00 parts by mass of carbon to 1.00 part by mass of hydrogen. How much hydrogen can be made from 90.0 g of methane?

Nitrous oxide, sometimes called “laughing gas,” can be decomposed to give 7.00 parts by mass of nitrogen and 4.00 parts by mass of oxygen. What mass of nitrogen is obtained if enough nitrous oxide is decomposed to yield 36.0 g of oxygen?

The gas ammonia can be decomposed to give 3.00 parts by mass of hydrogen and 14.0 parts by mass of nitrogen. What mass of nitrogen is obtained if 10.2 g of ammonia is decomposed?

We can express the ratio of parts by mass in any units we choose — pounds, grams, kilograms — as long as it is the same for both elements. Using grams as the units, we see that 3.00 g of C and 1.00 g of H would be produced if 4.00 g of CH4 were decomposed. To convert g CH4 to g H, we need a conversion factor that includes 1.00 g H and 4.00 g CH4.

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1803, John Dalton

Law of Multiple Proportions: Elements may combine in more than one set of proportions, with each set corresponding to a different compound.

John Dalton and the Atomic Theory of Matter

CONCEPTUAL EXAMPLE 2.2 Atom Ratios

Phosphine gas can be decomposed to give phosphorus and hydrogen in a mass ratio of 10.3 : 1.00. If the relative mass of phosphorus is 31.0 when the mass of hydrogen is taken to be 1.00, how many hydrogen atoms are combined with each phosphorus atom in the gas?

Solution

Exercise 2.2

Hydrogen sulfide gas can be decomposed to give sulfur and hydrogen in a mass ratio of 16.0 : 1.00. If the relative mass of sulfur is 32.0 when the mass of hydrogen is taken to be 1.00, how many hydrogen atoms are combined with each sulfur atom in the gas?

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John Dalton and the Atomic Theory of Matter

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• All matter is composed of extremely small particles called atoms.

• All atoms of a given element are alike and differ from the atoms of any other element.

• Compounds are formed when atoms of different elements combine in fixed proportions.

• A chemical reaction involves the rearrangement of atoms.

John Dalton and the Atomic Theory of Matter

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• Much of John Dalton’s atomic theory has been modified. For example, John Dalton assumed that all atoms of an element are alike. He did not understand the existence of isotopes.

• What is an isotope?• Isotopes are atoms of the same element with

different relative masses.• Relative atomic mass.

Isotopes

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1869, Dmitri MendeleevMendeleev arranged theelements in order of increasingAtomic Mass. Do the Mendeleev Card Activity!! ..then watch this: http://www.youtube.com/watch?v=0l_Z2zdT9gU

•He left gaps for yet undiscovered elements. •He also predicted the chemical & physical properties of those elements. •When those elements were discovered, many of his predictions were found to be accurate.•Was DM’s PT a model? Why?

Out of Chaos: The Periodic Table

CONCEPTUAL EXAMPLE 2.3 Predicting Periodic Properties

Solution

Exercise 2.3

In 1829, Johann Dobereiner, a German chemist, published his observations that there were several groups of three elements that were quite similar. In each case, the middle element seemed to be halfway between the other two in atomic mass, reactivity, andother properties. One such group, which he called alkali formers, was lithium, sodium, and potassium. Show that the relative atomic mass of the middle element in this triad is close to the average of the relative atomic masses of the other two elements.

The atomic mass of lithium (Li) is 6.941 u and that of potassium (K) is 39.098 u. The average of the two is (6.941 u + 39.098 u) ÷ 2 = 22.795 u, quite close to the modern value for sodium (Na) of 22.989 u.

Another of Dobereiner’s triads was the salt formers chlorine, bromine, and iodine. Show that the relative atomic mass of the middle element in this triad is close to the average of the relative atomic masses of the other two elements.

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Out of Chaos: The Periodic Table

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Out of Chaos: The Periodic Table

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Atoms: Real and Relevant

Atoms are a very real concept. It is even possible to observe computer-enhanced images of atoms.

An image that depicts a circular array of 48 iron atoms on a 7.3 nm copper surface, called a “quantum corral”, assembled by STM manipulation. 

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Leucippus Revisited: Molecules

Molecules are groups of atoms chemically bonded together.

A molecule of water is composed of two atoms of hydrogen (H) bonded to an atom of oxygen (O).

H2O

Check out this molecular modeling site: http://www.edinformatics.com/interactive_molecules/ice.htm