Early Chemistry – courtesy Ms. Borgatti

Processing ores and embalming fluids 1000 B.C. Early History of Chemistry Robert Boyle (1627-1691): He believed that science should be substantiated by experiments and looking at the properties of gases. He also began to define the element. Processing ores and embalming fluids 1000 B.C. In 400 B.C. the Greeks proposed all matter was made out of fire, water, earth, and air. Next 2000 years chemistry was dominated by alchemy. Some were fakes, trying to turn cheap metals into gold. Others were genuine scientists: learning the preparation of acids.

The Elements All of the material on the Earth is derived from about 100 different elements. If you think about it, it is pretty incredible to think that EVERYTHING that you see around you comes from only 92 naturally occurring building blocks. For example, proteins are made by linking together C, H, O in long complex chains. Without them, humans would not exist. Out of 118 known elements (as of March 2010), only 92 of them occur naturally. The rest have been manufactured in laboratories.

Mass Percent of Elements in the Earth’s Surface, Atmosphere, and Oceans Most Common: Oxygen 49.2% Silicon 25.7% Aluminum 7.5% Iron 4.71% Calcium 3.39% Sodium 2.63% Potassium 2.40% Magnesium 1.93%

Oxygen: Nearly half of the mass of all matter on Earth is made up of oxygen! Oxygen makes up about 20% of the Earth’s atmosphere… In what form does oxygen exist in the Earth’s atmosphere? O2 Also found in rocks, sand, and soil in the Earth’s crust. However, it is not usually found in element state. Usually the oxygen in these materials is located in other compounds that contain another element called silicon.

Mass Percent in the Human Body Most Common: Oxygen 65% Carbon 18% These elements present in the body, even those present in small amounts, play a crucial role in life. For example, Chromium, which helps the body use sugars to produce energy. Hydrogen 10% Nitrogen 3% Calcium 1.4% Phosphorus 1% Magnesium .5% Potassium .34%

What does the book mean when it says “Element”? Sometimes it means a single atom of that element. Sometimes the book means a large enough sample of atoms that can be weighed on a balance. It may even be an “elemental molecule”, like O2. You have to think carefully when you are reading the text in order to determine which definition of “element” applies!

Symbols for Elements The name of chemical elements generally come from the Latin, Greek, or German word that describes a property of the element. Example: Gold (originally from Greek word aurum) which meant “shining dawn”. Example: Lead (originally from the Greek word plumbum) which meant “heavy”. It is common for elements to also be named after the places where they were discovered. Example: Germanium, francium, californium. They can also be named after the scientists that discovered them. Example: Einsteinium and Nobelium.

Sodium = Natrium (Greek) = Na Iron = Ferrum (Greek) = Fe The rules behind the “Elemental Symbols” The symbol usually consists of the first letter or the first two letters of the elements full name. The first letter is always capitalized and the second letter is not. EXCEPTIONS Sometimes the two letter used are not the first two letters in the element’s name: Zinc = Zn Cadmium = Cd Chlorine = Cl Platinum = Pt Sometimes the symbols are based on Latin or Greek names that are no longer used in the Periodic Table. Sodium = Natrium (Greek) = Na Iron = Ferrum (Greek) = Fe

An “In-Depth” Look at Iron: Thought to be the main component of the Earth’s core. First evidence of human use of iron dates back to 4000 B.C. in the form of iron beads. Later, 3000 B.C., evidence of use of iron in weapons by one of the military cultures. Today iron is extremely important as it is one of the metals that makes up the alloy of steel. Most importantly, it is irreplaceable in human chemistry. Iron compounds in our blood allow us to absorb oxygen from the air and transport it to the tissues of our bodies. Assist oxygen in reacting with food to provide us with energy.

Evolution of Atomic Theory As scientists began to really look at materials in nature, they discovered several things… 1. Most natural materials are mixtures of pure substances. 2. Pure substances are either elements or combinations of elements called compounds. 3. A specific compound (ex. H2O) always contains the same proportions (by mass) of the elements. Ex. Any time you are dealing with water…. There are 8 grams of oxygen for every one gram of hydrogen. Chemical composition never changes in a compound.

John Dalton Born in 1766, he was an English scientist. Made his living as a teacher and private tutor in England. Interested in science at a young age and started a school in his village at age 12. As a young child he was fascinated by the weather and the atmosphere. He began recording the weather conditions every day for 46 years which has contributed much to the study of early world weather patterns. He was most famous for developing “Dalton’s Atomic Theory”.

Dalton's Atomic Theory - 1808 1. Elements are made out of tiny particles called atoms. 2. All atoms of a given element are identical. 3. The atoms of a given element are different from those of any other element. 4. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. 5. Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.

Law of Constant Composition: If a compound always contains the same relative numbers of atoms, it will always contain the same proportions by mass of the various elements. At this point in history, people believed Dalton’s theories because he was able to use them to successfully predict the chemical compound of nitrous oxide.

Law of Conservation of Mass : A chemical change is a rearrangement of atoms. Since atoms are neither created nor destroyed, mass is neither created nor destroyed --- i.e., mass is conserved.