Early History of Chemistry

Aristotle 350 B.C.

-Greek philosopher -agreed with Empedocles 4 elements -Added a 5th element- Aether which he said was the material of heavenly bodies such as stars and planets

Joseph Proust 1794

-Law of Definite Composition (Law of Definite Proportions)- a given chemical compound always contains its component elements in fixed ratio (by weight) and does not depend on its source and method of preparation. For example water is always composed of 11.2% hydrogen and 88.8% oxygen

Law of Definite Composition

-Law of Definite Composition (Law of Definite Proportions)- a given chemical compound always contains its component elements in fixed ratio (by weight) and does not depend on its source and method of preparation. For example water is always composed of 11.2% hydrogen and 88.8% oxygen

Law of Multiple Proportions

-Law of Multiple Proportions- If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers -For example, Dalton knew that the element Carbon forms two oxides by combining with oxygen in different proportions. A fixed mass of carbon, say 100 grams, may react with 133 grams of oxygen to produce one oxide, or with 266 grams of oxygen to produce the other. The ratio of the masses of oxygen that can react with 100 grams of carbon is 266:133≈2:1, a ratio of small whole numbers. Dalton interpreted this result in his atomic theory by proposing (correctly in this case) that the two oxides have one and two oxygen atoms respectively for each carbon atom. In modern notation the first is CO (carbon monoxide) and the second is CO2 (Carbon Dioxide

John Dalton 1804

-Law of Multiple Proportions- If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers -For example, Dalton knew that the element Carbon forms two oxides by combining with oxygen in different proportions. A fixed mass of carbon, say 100 grams, may react with 133 grams of oxygen to produce one oxide, or with 266 grams of oxygen to produce the other. The ratio of the masses of oxygen that can react with 100 grams of carbon is 266:133≈2:1, a ratio of small whole numbers. Dalton interpreted this result in his atomic theory by proposing (correctly in this case) that the two oxides have one and two oxygen atoms respectively for each carbon atom. In modern notation the first is CO (carbon monoxide) and the second is CO2 (Carbon Dioxide) -Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element. 3. Atoms of different elements can combine with one another in simple whole number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined or rearranged with each other. 5. Atoms of one element are not changed into atoms of another element by chemical reactions

What was the Phlogiston Theory?

-When an object burns it gives of Phlogiston + the ash weighs less than the starting material - Lavosier proposed the idea of combustion- when something burns it combines with oxygen and weighs more than the starting metal

J.J. Becher 1667

-believed in only 3 elements (replaced fire, water, and air with three forms of earth): terra leaped, terra fluid, terra pings -publishes physical subterranean proposing the Phlogiston theory -term phlogiston had been used as early as 1606 -phlogiston was "fire stuff" which was given off when something burned resulting in the ash weighing less

Joseph Priestley 1762

-discovered oxygen in the air and called it "dephlogisticated air" -continued to further support the Phlogiston Theory

Joseph Black 1756

-discovered that limestone reacts with acid to produce a gas that is denser than air and did not support a flame or animal life. He called this gas fixed air -since this gas is also found in air but air supports a flame and animal life, air must be a mixture and not an element.

Antoine Lavoisier 1777

-disproved the Phlogiston theory -proposed the idea of combustion- when something burns it combines with oxygen and weighs more than the starting metal -law of conservation of Mass- Mass can neither be created nor destroyed, although it may be rearranged in space, or the entities associated with it may be changed in form, as for example when light or physical work is transformed into particles that contribute the same mass to the system as the light or work has contributed. Thus, during any chemical reaction, nuclear reaction, or radioactive decay in an isolated system, the total mass of the reactants or starting materials must be equal to the mass of the products

Empedocles 450 B.C.

-greek philosopher -proposed idea of 4 'elements' -did not use the word elements, instead called them roots -idea of 4 roots was held true for nearly 2000 years

Democritus 400 B.C.

-greek philosopher -Atomism- nature consists of two fundamental principles: atom and void -atoms are uncuttable

The Law of Multiple proportions was based on certain assumptions. Which of these assumptions are known to be untrue? What other assumptions that Dalton made about matter turned out to be untrue?

-particles of gas are not close together -the simple compounds of two elements are not always formed, sometimes more complex ones are formed

Georg Stahl 1703

-student of Becher -reworked Becher idea of the Phlogiston Theory and published terra pinguis to phlogiston -"To Stahl, metals were compounds containing Phlogiston in combination with metallic oxides (calces); on ignition the phlogiston was freed from the metal leaving the oxide behind. When the oxide was heated with a substance rich in phlogiston, such as charcoal, the calx again took up Phlogiston and regenerated the metal. Phlogiston was a definite substance, the same in all its combinations."

Atomic Theory

1. All elements are composed of tiny indivisible particles called atoms (Not true- protons, neutrons, electrons) 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element. (false- isotopes: different versions of elements- for every element on periodic table- multiple versions of that element 3. Atoms of different elements can combine with one another in simple whole number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined or rearranged with each other. (true) 5. Atoms of one element are not changed into atoms of another element by chemical reactions (true, not change by chemical reactions but will change by radioactive decay)

What was John Priestly's contribution to understanding combustion?

Joseph Priestly discovered oxygen

How did Lavoisier prove that the Phlogiston Theory is not true?

Lavoisier put mercury into a sealed vessel and heated it for several days. During heating, he noticed the mercury turned into a red powder but the mass of the vessel and the contents did not change. When he opened the vessel, he heard air rushing inside and the mass of the vessel increased. The difference in mass increased strongly heating the red powder gas off oxygen that supported burning. He proposed that combustion is the combination of a substance with oxygen.

Law of conservation of Mass

Mass can neither be created nor destroyed, although it may be rearranged in space, or the entities associated with it may be changed in form, as for example when light or physical work is transformed into particles that contribute the same mass to the system as the light or work has contributed. Thus, during any chemical reaction, nuclear reaction, or radioactive decay in an isolated system, the total mass of the reactants or starting materials must be equal to the mass of the products