Discovering the Atom and Subatomic Particles Chapter 3.1—3.3 Notes

Let’s start with some history.. Aristotle Greek philosopher that lived from 384—322 B.C.) Described composition and behavior of matter in terms of four different qualities: hot, cold, moist, and dry Democritus Another Greek philosopher (460—370 B.C.) “matter is composed of a finite number of incredibly small but discrete units we call atoms.” Coined the term atom from the Greek phrase atomos, meaning “not cut” or “that which is indivisible” The texture, mass, and color of a material are a function of the texture, mass, and color of its atoms.

What is an element? Aristotle said that any substance could be changed from one substance to another by simply changing one of the 4 basic qualities (hot, cold, moist, dry) Meaning, we could change lead to gold Alchemy: a field of study concerned primarily with finding potions that would produce gold Robert Boyle (1627—1691) goes against Aristotle and says that a substance is not an element if it is made of two or more components Antoine Lavoisier (1743—1794) says that an element is any material made of only one component Identified a compound as any material composed of two or more elements

Lavoisier Recall from chapter 2: definitions of compound and element Lavoisier’s ideas are in line with our present understanding His definitions required experimentation—Greek philosophers simply based their ideas on logic and reason. Lavoisier considered the “father of modern chemistry”

Law of Conservation of Mass Lavoisier hypothesized that mass is always conserved during a chemical reaction Conserved means the mass does not change The number of grams of mass present after the reaction is the same as the number of grams present before the reaction

Law of Conservation of Mass Formally states: There is no detectable change in the total mass of materials when they react chemically to form new materials. Let’s think about it: If I burn a piece of wood, does the wood weigh the same after as it does before? Why? Lavoisier accounted for gases! When the wood burns, gaseous carbon dioxide and water vapor are released!

Discovery of Oxygen Joseph Priestly ( ), an English chemist, had prepared and isolated a gas. First to recognize the nature of carbonated beverages Collected oxygen gas by heating the highly toxic compound mercury oxide, HgO—turns into liquid mercury and oxygen gas when heated. The gas couldn’t be broken down to simpler substances so Lavoisier classified it as an element. The gas could be used to produce acidic solutions; Lavoisier called it oxygen, meaning “acid former.”

Discovery of Hydrogen Henry Cavendish, English chemist, isolated a gas that could be ignited in air to produce water and heat. Lavoisier recognized this gas was an element, and he named it hydrogen (Greek word for “water former.”) Hydrogen reacts with atmospheric oxygen to form water, therefore water is a compound Aristotle had claimed that water was an element

Law of Definite Proportions Joseph Proust, French chemist, that noted that whenever hydrogen and oxygen react to form water, it is always in the same ratio. 8 grams of oxygen react with 1 gram of hydrogen to produce 9 grams of water; 32 grams of oxygen react with 4 grams of hydrogen to produce 36 grams of water. Law of Definite Proportions: Elements combine in definite mass ratios to form compounds.

Dalton’s Postulates John Dalton (1766—1844), self-educated English schoolteacher 1. Each element consists of indivisible, minute particles called atoms 2. Atoms can be neither created nor destroyed in chemical reactions 3. All atoms of a given element are identical 4. Atoms chemically combine in definite whole-number ratios to form compounds 5. Atoms of different elements have different masses

Diatomic Molecules Amadeo Avogadro (1776—1856), Italian physicist and lawyer 2 atoms per molecule at standard temperature and pressure H 2, N 2, O 2, F 2, Cl 2, I 2, Br 2

“Father” of the Periodic Table Dmitri Mendeleev (1834—1907), Russian chemistry professor Produced a chart summarizing the properties of known elements Arranged the elements based on their properties Sometimes there were blanks that could not be filled by any known elements; he left these open and others eventually discovered the missing elements

Place the following in chronological order: a. Elements are made of atoms b. Hydrogen gas and oxygen gas consist of diatomic molecules c. The periodic table can be used to predict the properties of elements d. Mass is conserved during a chemical reaction