- Elements are pure substances that cannot be broken down further without losing their identity, and there are currently 118 known elements, with 88 occurring naturally. - In the universe, hydrogen makes up 75% and helium 20%, while on Earth oxygen is the most abundant element in the crust at 46.6% and silicon is second most at 27.7%. - Compounds are pure substances made of two or more chemically bonded elements, with properties different from the individual elements, and can be represented by chemical formulas showing the elements and their ratios.

1. Elements and Compounds A Mr. Mularella Presentation

2. The 4 Ancient Elements Earth Fire Air Water

3. Elements There are currently 118 elements that have been identified though only 88 of them are naturally occurring.

4. Elements in the Universe In our universe, hydrogen makes up 75% of all matter! Helium makes up about 20% with oxygen being the 3 rd most abundant element. All of the other elements are relatively rare in the universe.

5. Elements in the Earth In the Earth’s crust, oxygen is the most abundant element (46.6%). Silicon is the second most abundant element (27.7%). Aluminum (8.1%), iron (5.0%), calcium (3.6%), sodium (2.8%), potassium (2.6%). and magnesium (2.1%) complete the list of elements that account for approximately 98.5% of the total mass of the earth's crust.

6. Elements Elements are a pure substance. Made of only one kind of material, has definite properties, and is the same all throughout. Elements are the simplest pure substance. They cannot be broken down into simpler substances without losing their identity.

7. Elements and Atoms The smallest particle of an element that has the properties of that element is called an atom . Atoms: the building blocks of matter. Atoms of the same element are alike; atoms of different elements are different.

8. Chemical Symbols Shorthand way of representing the elements. Usually one or two letters. Usually taken from the name of the element. Carbon-C, Calcium-Ca, Hydrogen-H, Iodine-I, Oxygen-O, Chlorine-Cl

9. Chemical Symbols Some symbols come from their Latin name: Gold-Au--aurum Silver-Ag--argentum Iron-Fe--Ferrum Mercury-Hg--hydrogyrum

10. Compounds Pure substances made up of more than one element. 2 or more elements chemically combined. Ex: H 2 O, NaCl, C 6 H 12 O 6 , CO 2 Unlike elements, compounds can be broken down to simpler substances. This can happen through a chemical reaction.

11. Compounds The properties of the elements that make up a compound are often quite different from the properties of the compound itself. Sodium-Na--highly reactive metal Chlorine-Cl--poisonous gas Sodium Chloride-NaCl--table salt

12. Molecules Compounds are made of molecules. A molecule is 2 or more atoms chemically bonded. Water-2 atoms of hydrogen and one atom of oxygen-together they form one molecule of H 2 O. A molecule is the smallest particle of a compound that has all the properties of that compound. Just as all atoms of a certain element are alike, all molecules of a certain compound are alike.

13. Chemical Formulas A shorthand way of representing compounds. If chemical symbols are the “letters,” these are the “words.” Ex: NH 3 - ammonia, C 3 H 7 OH - rubbing alcohol Sometimes, the formula represents a molecule of a single element. These are called diatomic molecules. This is how that element is naturally found. O 2 -Oxygen H 2 -Hydrogen Cl 2 -Chlorine

14. Chemical Formulas Subscripts are small numbers used in chemical formulas. They are placed to the lower RIGHT of the chemical symbols. Represent # of atoms of an element in a compound. CO 2 = 1 atom of carbon and 2 atoms of oxygen. H 2 SO 4 = 2 atoms of hydrogen, 1 atom of sulfur and 4 atoms of oxygen