Review+of+elements,+compounds+and+mixtures

media type="custom" key="2627187" [|On line practice: recognize elements, compounds and mixtures] Name_ || about what you do in your math classes when you are multiplying: 4 x (**CO** ** 2 ** ).
 * [[image:file:C:%5CDOCUME%7E1%5COwner%5CLOCALS%7E1%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_image002.jpg width="4" height="1"]] media type="custom" key="2364215"
 * ** Making Molecules ** ||
 * ** Background Information ** : An **__element__** is a substance consisting of a single type of ||
 * atom. There are 92 naturally occurring elements in the world; yet there are many, many ||
 * more types of matter. These different types of matter are combination of elements. A ||
 * particular type of combination of elements is a compound. ||
 * A chemical **__compound__** is a chemical substance formed from two or more elements in a ||
 * specific proportion. The elements lose their individual chemical properties and the ||
 * compound has new properties. A **__molecule__** is the smallest unit of a compound that can ||
 * exist alone and keep the properties of that compound. Molecules are made up of one ||
 * or more atoms. If they have more than one atom, the atoms can be the same (an ||
 * oxygen molecule has two oxygen atoms) or different (a water molecule has two ||
 * hydrogen atoms and one oxygen atom). Molecules in living organisms, such as proteins ||
 * and DNA, can be made up of many thousands of atoms. ||
 * Compounds are written using **__formulas__**. The chemical formula of a molecule or ||
 * compound shows how many atoms of each element are in one molecules of the ||
 * compound. Formulas are written by putting the element symbols next to each other. If ||
 * there is //more than one atom of an element// in the molecule, the formula shows it by a ||
 * // small number after the symbol // of that element. This number is called a **__subscript__**. //No// ||
 * // number // after an element’s symbol is understood to mean //one atom of that e//lement is ||
 * present. ||
 * //__ For example __//, the formula for water is **H** ** 2 **** O ** , which means there are 2 atoms of hydrogen ||
 * and one atom of oxygen in the molecule. Carbon dioxide is **CO** ** 2 **, which means there is ||
 * one atom of carbon and two atoms of oxygen in the molecule. ||
 * To show the number of molecules, a number is put in front of the molecule. This number ||
 * is called a **__coefficient__**. ||
 * //__ For example __// 4 molecules of carbon dioxide are written as: **4CO** ** 2 ** ||
 * This means there are a total of **4** **C** atoms and **8 O** atoms in the combination. Think ||

** From the name of a //chemical//, determine whether it is an element or compound. ** The first objective says that from the name of the chemical you should be able to determine whether it is an element or a compound. Doing that essentially involves recognizing the names of the elements, and then if you are dealing with something that combines more than one element, then you are dealing with a compound. Example: a. water, H2O (a) Water: Water is one of those things that you should just recognize by name and recognize that it consists of hydrogen and oxygen and therefore water is a compound. The second objective says that from the chemical symbol or chemical formula you should be able to determine the name of the element or compound. Example: a. H2 b. NaCl (a) H2: is an element beacuse it has only one kind of atom in its composition. It is also a molecule because it has more tnam one atom (diatomic molecule) (b) NaCl: Sodium chloride is a compound beacuse it has more than one kind of atom in its composition.

From the name of an //element//, determine whether it is a metal, a nonmetal or an inert gas.
The second objective says that from the name of an element you should be able to determine whether it is a metal, nonmetal or an inert gas. To do that, you either have to rely on your recognition of these things, or consult a periodic table. The elements which are found on the left side up to the diagonal line that includes aluminum are going to be the metals. The nonmetals will include the other elements up and to the right of that diagonal line and also hydrogen with the exception of the last group of elements on the periodic table, which are the inert gases.

Example: Which of the following elements are metals, which are nonmetals and which are inert gases? a. phosphorus b. Helium d. magnesium Answers: Phosphorus is a non metal, Helium is a noble gas or inert gas and magnesium, Mg is a metal.

Obj. 3. From the name of an **//element//**, determine whether it has metallic, covalent or ionic bonding.
In order to do this, you have to decide whether the element that you are dealing with is a metal or a nonmetal, the same kind of thing that we just did in the previous example. Metallic bonds occurs between metal, so if an atom of Fe bonds to another atom of Fe, we call that type of bond, metallic. Likewise, if two non metals, like C and O form a bond, we will have a covalent bond. Ionic bond occurs when a metal reacts with a non metal, the bond in the new compound will be ionic.

Obj. 3. Determine if the substance is pure (element/ compound) or mixture
A ** pure substance ** is a form of matter that has a definite composition and distinct properties. It may consist of only one type of atoms ( examples: Fe(s), N 2 (g), S 8 (s)), or of only one compound where the atoms are connected in a defined way, ( examples: FeS(s), CH 4 (g), NaNO 3 (s), H 2 O(l)). Many substances called “pure” in everyday life like “Pure Honey”, “Pure Silk” etc. are not pure in a scientific sense but they are mixtures.

Examples; a. H and H pure (element) b. Na and Cl pure (compound) c. Water and NaCl Mixture

[|Separation of mixtures] 