Scientist used to believe that matter was made up of four elements (air, earth, fire and water).

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2 Scientist used to believe that matter was made up of four elements (air, earth, fire and water). We now know that all matter in the universe is made of slightly more than 100 different substances called elements.

3 Element - a pure substance that cannot be broken down into any other substances by chemical or physical means. Gold Elements are the simplest substances. Copper Iron

4 The elements do not only exist alone they combine with other elements to make all the matter in the world. All living things, including humans, are made mostly of just six elements The six elements found in the amount in living things are: Nitrogen Carbon Hydrogen Oxygen Phosphorous Sulfur The way to remember it this is N CHOPS. Pork Chops, N CHOPS

5 Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on their mass He lived from

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7 Atomic number is on top The symbol is in the middle. Can be one capital letter like O for oxygen Can be one capital letter and one lowercase like Au for gold when there are two letter abbreviations. Element name MAY OR MAY NOT BE LISTED WITH THE SYMBOL! The atomic mass is below the symbol.

8 The periodic table was originally organized by increasing mass (Mendeleev). The modern periodic table is organized by increasing atomic number. The number starts at 1 with Hydrogen, increases going to the right with Helium, 2. It then jumps down a row and starts to the far left with Lithium, 3 and continues with this pattern until you get to the sixth row and we will discuss.

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10 Period the name for each row of elements (left to right) Family the name for each column of element ( up and down)

11 THE PERIODIC TABLE PICTURES

12 What is the smallest possible piece of matter? All matter is made up of atoms. Atom - is the basic particle from which all elements are made.

13 All atoms are made of the same 3 subatomic (smaller than an atom) particles. Protons Electrons Neutrons

14 Different elements have different properties because their atoms are different. The hydrogen atom has 1 proton and 1 electron The helium atom has 2 protons, 2 neutrons, and 2 electrons.

15 Atoms are made of protons (+), neutrons (no chargeneutral), and electrons (-). The number of protons determines which elements can be formed from the atoms Remember, the atomic number of an element tells you the number of protons in that element

16 Atoms of most elements have the ability to combine with other atoms. When atoms combine, they form a chemical bond, Chemical Bond - a force of attraction between two atoms.

17 In many cases, atoms combine to form larger particles called molecules. Molecules when two or more atoms join together by chemical bonds. For Example: A molecule of water is made of a 2 different elements and three atoms total, H 2 O. H 2 atoms of Hydrogen as shown by the subscript 2 O 1 atom of Oxygen (anytime there is not a subscript after an element, it is assumed to be a 1) (we will discuss this again)

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19 Two atoms of the same element can also combine to form a molecule. Oxygen molecules consist of two oxygen atoms. There are 7 elements that combine to form DIATOMIC molecules in nature Hydrogen (H 2 ), Nitrogen (N 2 ), Oxygen (O 2 ), Fluorine (F 2 ), Chlorine (Cl 2 ), Bromine (Br 2 ), and Iodine (I 2 )

20 Compound - a molecule that contains at least two different elements All compounds are molecules BUT not all molecules are compounds. Remember..A molecule is formed when two or more atoms join together chemically. Diatomic hydrogen (H 2 ), diatomic oxygen(o 2 ) and diatomic nitrogen (N 2 ) are not compounds because each is composed of a SINGLE element. Water (H 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) are compounds because each is made from more than one element. The smallest bit of each of these substances (COMPOUNDS) would be referred to as a molecule. For example, a single molecule of diatomic hydrogen is made from two atoms of hydrogen while a single molecule of water is made from two atoms of hydrogen and one atom of oxygen.

21 CO 2 The number 2 below the symbol for oxygen tells you that the ratio of carbon to oxygen is 1 to 2. There is 1 Carbon atom for every 2 Oxygen atoms. (Anytime there is not a subscript after an element, it is assumed to be a 1)

22 If a different ratio of carbon atoms to oxygen atoms are seen in a formula, you have a different compound. CO Carbon to oxygen ratio is 1 to 1. There is 1 Carbon atom for every 1 Oxygen atom. For example, Carbon Monoxide a gas produced in car engines has the formula CO. Carbon Dioxide a gas we exhale has the formula CO 2

23 When elements are chemically combined, they form compounds having properties that are different from those of the uncombined elements.

24 SULFUR AND SILVER - UNCOMBINED For example, the element sulfur is a yellow solid and the element silver is a shiny metal. SULFUR AND SILVER BONDED IN A COMPOUND When silver and sulfur combine, they form a compound called silver sulfide, Ag 2 S. You would call this black compound tarnish.