Chemical Compounds Chapter 20

A. Elements that combine chemically no longer have the same properties B. Chemical Formulas are composed of symbols and subscripts that indicate the number of atoms of each element

C. Atoms form compounds when the compound is more stable than separate atoms 1. Noble gases have complete outer shells, so they are more chemically stable 2. Elements that do not have complete outer shells are more reactive, but are more stable as compounds than elements 3. Atoms can lose, gain, or share electrons 4. A chemical bond is the force that holds atoms together

20.2 A. An ion is a charged particle 1. When an atom loses an electron it becomes positively charged (has more protons than electrons) 2. When an atom gains an electron it becomes negatively charged (has less protons than electrons) Some examples are sodium chloride, commonly known as table salt; sodium fluoride, an anticavity ingredient in some toothpastes; and potassium iodide, an ingredient in iodized salt.

B. Ionic Compounds: Held together by an ionic bond when atoms gain/lose electrons 1. The result is a neutral compounds 2. Net sum of charges is zero

C. Molecules are formed as a result of sharing electrons 1. A Covalent Bond is the force of attraction between atoms sharing electrons, a molecule is formed 2. Can form double or triple bonds 3. Electrons are held more closely to the atoms with the larger nucleus

A Polar molecule has one negative and one positive end 5. A Nonpolar molecule both ends are either positive or negative Polar or Nonpolar??

20.3 Writing and Naming Chemical Formulas Use Symbols to represent elements in writing formulas Binary Compounds are composed of two elements Oxidation Number- How many electrons an atom has gained, lost, or shared until it becomes stable Use Oxidation Numbers to write formulas a. Compounds are always neutral b. A formula must be balanced, by having the same amount number of positive and negative ions In writing a formula use the name of the first element, the root name of the second element, and the suffix - ide to write the name of the compound. *Oxidation Numbers used only in IONIC Bonds*

Polyatomic Ion- Positively or Negatively charged atoms 1. Contains three or more elements 2. Write the name of the positive ion first, then the name of the negative ion second To write formulas use the oxidation numbers, their least common multiple, and put parentheses around the ion before adding a subscript to represent the number of atoms

Hydrate compounds have water chemically attached to the ions Name the binary (2 elements) covalent (shared) compound by using prefixes to indicate how many atoms of each element are in the compound Examples: Carbon Dioxide: CO2 Carbon Monoxide: CO *Prefixes used only in COVALENT Bonds *

Practice Naming COVALENT Binary Compounds: Silicon Dioxide Iodine Trichloride Dihydrogen Oxide SiO2 ICl3 H2O N2O5 CaCr2 Na4Cl DiNitrogen PentaOxygen Calcium DiChromide Tetrasodium Chlroide

Practice Naming IONIC Binary Compounds Sodium bromide 2. Silicon oxide 3.Lithium carbonite Oxidation Number of Na= +1 Br= -1  NaBr Oxidation Number of Si= -4 O= +2  Si2O4  SiO2 Oxidation Number of Li = +1 C= -4  Li4C