Chemical Bonding Physical Science Chemical Bonds n n

Chemical Bonding Physical Science

Chemical Bonds n n When two or more atoms attach to each other, they form a chemical bond Compounds are any two elements chemically bonded n n n Water Sugar Salt And almost all other substances!!!! Electrons are responsible for the type, strength, and size of a chemical bond

Lewis Structures n n n Bohr-Rutherford diagrams are large and difficult to show relationships between multiple atoms Lewis diagrams are used to show multiple atoms Lewis diagrams show only the valence electrons

Lewis Structures n n Valence electrons form the charge of an atom Electrons are always trying to get together in groups of 8 (forget shells for a minute) Elements that have 8 valence electrons have FULL outer groups We call these elements NOBLE or INERT gases, they are found in group 8

Lewis Structures n Label the Nobel (Inert) gases on your chart

Lewis Structures n Elements with 1 valence electron are called the Alkali metals (group 1) (Label)

Lewis Structures n Elements with 2 valence electrons are called the Alkaline Earth metals (group 2) (Label)

Lewis Structures n Elements with 7 valence electrons are called the Halogens (group 7) (Label)

Lewis Structures n Consist of n n Element Symbol Electrons in each open spot Sy

Lewis Structures n n n 7 Draw the element symbol Determine the # valence electrons Starting at the top, going clockwise, place one electron in each spot around the element symbol Cl

Lewis Structure n Draw the Lewis Structure for Aluminum! Al

Quick Recap! n n Draw the Lewis Structure for Lithium! Draw the Rutherford-Bohr Diagram for Lithium! - Li 3 P 3 N -

A note about charges… n Writing a charge n n n Valence electrons, Bohr-Rutherford, and Lewis diagrams are used to determine charge Charges are a shortcut to determining bonding properties RULES OF CHARGE n n n IF the # of valence electrons is GREATER than 4, the charge is negative (Mostly) IF the # of valence electrons is less than 4, the charge is positive (Mostly) Charges are in reference to a full shell of 8

A note about charges… n For example, Aluminum has 3 valance electrons The possible charges are +3 OR -5 n It either has 3 OVER a full shell, or 5 LESS than a full shell n Because the number 3 is less than 4, we use the charge of +3 n

Charges +1 Nitrogen? -3 Sodium? n n Any element with a charge is called an ION, the charge is an ionic charge What are the ionic charges of the elements in the table? Oxygen? Argon? -2 0

Charges

Charges n A few exceptions! Metals are always a positive charge!! n Non metals are always negative!! n Metalloids can go either way (you are not responsible for choosing – I will tell you) n n Example: Boron According to rule of 4’s…. its a +3 charge n But since it’s a nonmetal, we use -5! n

Rules of Bonding 1. 2. 3. 4. All compounds must have neutral charges (That means the positive charges (cations) and the negative charges (anions) must equal Subscript numbers are used to show the number of ions Coefficients are used to show the number of molecules

Rules of Bonding 2 H 2 O Coefficient Subscript 1 atom of O “ 1’s” are implied and not written Subscript 2 atoms of H

Rules of Bonding H 2 O H H O

Rules of Bonding H 2 O O H H

Rules of Bonding n Try this one! Na. Cl (table salt) Na Cl

Rules of Bonding n Last One! Aluminum Bromide Br Al Br Br

Chemical Bonding n Several Types including Covalent Bonds* n Ionic Bonds* n Metallic (only between metals) n

Covalent Bonds n n n Electrons are shared between two or more atoms Covalent bonds can exist between atoms of the same type…for example N-N (N 2) or O-O (O 2) Covalent bonds can form single, double, or triple bonds Covalent bonds are strong and usually result in stable molecules Carbon always forms covalent bonds and forms the basic molecules for all life substances

Ionic Bonds n n Usually formed by members of the Alkali group (ones with +1 electron) Electrons are donated to another molecule Between elements from opposite sides of the chart Forms crystals (salts) & most dissolve in water

Forming Compounds 1. 2. 3. 4. Write ions with charges Cross charges Write subscripts (omit “ 1’s”) Use parenthesis if needed

Forming Compounds n What is the molecular formula of water? +1 H H 2 -2 O O 1 H 2 O O H H

Forming Compounds n What is the molecular formula of carbon dioxide? +4 -2 C O C 2 O 4 C 2 O 4 CO 2 Yikes! Reduce like a fraction to lowest denominator ****note****

Forming Compounds n What is the molecular formula of a compound that has aluminum and sulphur? +3 -2 Al S Al 2 S 3 Al 2 S 3 Any guesses on the name?