Chapter 6 p. 98-116 Bonding

What is a Chemical Bond? Chemical bonds provide the “glue” that holds all compounds together An attraction between the protons of one atom and the electrons of another What is the charge of a proton? What is the charge of an electron? The atoms will either SHARE or TRANSFER electrons Different bonds account for different properties of a substance The atoms will then have a complete outer shell and be STABLE, like a noble gas The actual bond has stored (potential) energy When a bond is broken, energy is absorbed An ENDOTHERMIC process When a bond is formed, energy is released An EXOTHERMIC process Remember, BARF! Because of this, compounds have lower energy then the atoms themselves This also causes the stability of the system to INCREASE

Examples: Broken or Formed? Absorbed or Released? 2H2 + O2 => 2H2O NaCl => Na + Cl 4K + O2 => 2K2O N + N => N2

Lewis Dot Diagrams- Atoms Also called Electron Dot Diagrams Find number of electrons in last energy level Called the ? Place the element symbol in the middle Represents the atom and all of its full shells Place dots, circles, or x’s all around the element symbol to represent the electrons Start with 2 dots (if there are 2 valence electrons) on one side of the element symbol Then 1 dot at each of the 3 other sides until the electrons are done MAX is 8! If there are still more electrons, make the rounds again.

Examples: Al Ca H Cl Ne

Lewis Dot Diagrams- Ions The valence shell SHOULD be FULL! Place the element symbol in the middle Represents the atom and all of its full shells Metals: Lose valence electrons Brackets around the symbol POSITIVE charge outside the bracket Non-Metals: Gain valence electrons Bracket and EIGHT DOTS around the symbol NEGATIVE charge outside the bracket

Examples: Na + S -2 Mg +2 Cl -

Lewis Dot Diagrams- Compounds Write the symbols of the 2 elements Place the valence electrons around the symbols Start with 2 at the top, then add one to each of the other sides until the valence is full One element should have circles or dots The other element should have x’s (usually) Both elements should have FULL valence electron shells Every TWO dots represent TWO electrons. They can also be drawn as ONE line

Examples Draw H2 Draw H2O Draw CO2 Draw HCl

Open your book to p. 99 (1-5) 2 1 3

Now, open your book to p. 102 3 See Board 4

Octet Rule Atoms will gain, lose, or share one or more valence electrons in order to achieve a complete outer shell of 8 VALENCE ELECTRONS A complete octet of eight valence electrons results in an exceptionally stable electron configuration This is why noble gases are so unreactive

There are 3 types of bonds that can be made: Metallic Ionic Covalent

1- Metallic Bonds Occurs ONLY in metals Positive ions in a “sea” of mobile electrons The negative electrons are attracted to the positive ion and that’s what holds the metal together Properties of Metals (Metallic bonds) Low ionization energy Malleable and ductile Because of moving valence electrons Hard Good conductors of heat and electricity In a solid and a liquid Because of MOBILE ELECTRONS High melting and boiling points

Open your book to p. 103 3 2 (it’s a metal!) 1

Remember, Electronegativity Atom’s attraction for electrons in a bond Higher the electronegativity, the more the atom attracts electrons Lower the electronegativity, the weaker is the attraction for electrons Table S, Column 5 Measured on a scale of 0-4

Ionic or Covalent Bond To find out the type of bond that exists: Look at the electronegativity for the 2 atoms bonding Subtract their electronegativity Absolute value! If the EN difference is > 2.0 = IONIC If the EN difference is < 2.0 = COVALENT

Ionic Bond: YES or NO Hydrogen and Chlorine Sodium and Chlorine Potassium and Bromine HBr HF 2.1-3.2 = 1.1 No 0.9-3.2 = 2.3 YES! 0.8-3.0 = 2.2 YES! 2.1-3.0 = 0.9 No 2.1-4.0 = 1.9 YES Remember, If the difference is 2.0 or more, it is an ionic bond

2- Ionic Bonds Elements that form ionic bonds will try to achieve the OCTET RULE Occurs between a metal and a non-metal Formed when a metal transfers one or more electrons to a nonmetal Metals lose e- and non-metals gain e- Non-metals have higher electronegativities and will strip away e- from metals which have lower electronegativities

Ionic Substance Characteristics They have IONIC BONDS Hard Good conductors of electricity ONLY when dissolved in water In aqueous solution (aq) and a melted liquid (l) NOT in SOLID form Ions carry a charge and can’t move in a solid High melting and boiling points Due to the STRONG attraction of the ions

Ionic Character To determine which compound has the greatest/ least ionic character, subtract the electronegativities of each element. The compound that has the greatest EN difference = greatest ionic character. The compound that has the smallest EN difference = least ionic character.

Ionic Substance Lewis Dot Diagrams Metals Write the Symbol of the Element With brackets because its an ion Look at the Oxidation Number If there is more than one, look at the first one Remember, that’s how many e- it will lose Write the Oxidation number next to the Symbol Nonmetals Place a bracket [ ] around the symbol and the 8 dots Remember, this is how many e- it will gain

Let’s do Some Examples Sodium Chloride Potassium Bromide Hydrogen Fluoride Magnesium Oxide Na2O CaCl2

Open your book to p. 110 (26-37) H h

Covalent Bonds Formed when two atoms SHARE electrons NO TRANSFER OF ELECTRONS Occurs between NON-METALS Very STRONG bond To find out if a covalent bond exists: Subtract the electronegativity If the answer is less than 2.0, it is a covalent bond

Covalent Bonds Character Molecular substances (have covalent bonds): Soft Poor conductors of heat and electricity There aren’t any charged particles to carry the electricity Low melting points and boiling points Remember the word “SPLash” Opposite properties as an ionic bond

Covalent Bonds Atoms can share a number of electrons More than just 2 Each pair of electrons that is shared, will form a bond For example: 1 pair (2 electrons) = single bond H - Br 2 pairs (4 electrons) = double bond O = C = O 3 pairs (6 electrons) = triple bond H - C = C - H

Covalent Bonds 3 types of covalent bonds: 1- Nonpolar covalent Electrons are shared equally EN difference between the elements is 0 Diatomic molecules 2- Polar covalent Electrons are shared unequally 2 different non-metals EN difference between 0.1-1.6 The element with the greater EN pulls stronger and gets a partial negative charge WATER!!!!!! 3- Coordinate covalent When one atom donates both of the electrons that are shared NH3 plus H+ get you NH4+ (ammonium ion) H2O + H+ -> H3O+ (hydronium ion) Always has a charge

Lets do some examples: Cl2 H2S NH3 H2O NaCl NH4+ Tell me the electronegativity, the difference, the type of bond, and draw the structure Cl2 H2S NH3 H2O NaCl NH4+

Polar Character To determine which compound has the greatest/least polar character, subtract the EN of each element. The compound that has the greatest EN difference = most polar. The compound that has the smallest EN difference = least polar.

Shape of Covalent Molecules Non-Polar Molecules Symmetrical Looks the same! Polar Molecules Asymmetrical

Non-Polar Bonds and Non-Polar Shape There are only ONE TYPE of molecule that can have a : Non-polar bond AND non-polar shape DIATOMIC MOLECULES!!!!!

Polar Bonds and Non-Polar Shape UNEQUAL sharing of electrons, but SYMMETRICAL shape CO2, CH4, CF4

Open your workbook up to p. 105-108 (13-25)

Summary of Bonds Ionic Transfer Electrons Difference in electronegativity of 1.7 or more Hard Good conductors when melted or in an aqueous solution Because of the movable ions High melting and boiling points Brackets! Covalent Share electrons Difference in electronegativity of less than 1.7 Soft Poor conductors of heat or electricity Low melting or boiling points SPLash Different types of bonds

Summary of Bonds-Covalent Nonpolar Covalent Equally share electrons Diatomic Molecules Same electronegativies Octet rule Usually has symmetrical shape Polar Covalent Unequal sharing of electrons Different electronegativites Also, octet rule Asymmetrical shape

Summary of Bonds Coordinate Covalent One element donates BOTH electrons to the bond Always will have a charge to it Metallic Bonds ONLY metals Mobile electrons Hard Good conductors in a solid and liquid state High melting and boiling points

STUDY FOR YOUR TEST!!! 