Chemistry Tuesday!!!!! 1/24/12 Bell Ringer Schedule 1. Pick up the Ionic bond packet off the front demo table. Write down and answer the following questions on your packet somewhere. A. Identify the valence electrons and electron dot drawing of the following elements: Li Ca Al C P S F Ne Bell Ringer Ionic & Covalent Bonding Demo Ionic/Covalent Bonding Notes HOMEWORK: Practice problems in your packet I CAN… compare and diagram ionic and covalent bonding.

Li Ca Al C P S F Na

Chemical Bonding and Molecular Structure Cartoon courtesy of NearingZero.net

Bonding Chemical Bond attractive force between atoms or ions that binds them together as a unit bonds form in order to… decrease potential energy (PE) increase stability

Intra VS Intermolecular Forces INTRA within INTER between, among Intramolecular force: bonds between atoms or ions in molecules Examples: metallic, covalent, & ionic bonds Hydrogen bonds to oxygen and forms water Intermolecular force: attraction between molecules themselves Intermolecular forces are only associated with covalently bonded molecules (glucose & fructose hydrogen bridge to make sucrose) 3 different levels of strength: 1) Hydrogen Bridge (used to be called H bond) (strongest) 2) Dipole-dipole forces 3) London Dispersion forces (weakest) (covalently bonded molecules have this) Water molecule attracted to another water molecule

Review of Chemical Bonds There are 2 main types of bonding: IONIC—transfer of 1 or more valence electrons COVALENT—sharing of valence electrons “Between ionic and covalent most bonds are”

The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together.

Electronegativity Difference If the difference in electronegativities is between: 1.7 to 4.0: Ionic 0.3 to 1.7: Polar Covalent 0.0 to 0.3: Non-Polar Covalent Example: NaCl Na = 0.8, Cl = 3.0 Difference is 2.2, so this is an ionic bond!

Ionic Bonds Ions are positively or negatively charged atoms due to the removal or addition of an ELECTRON CATION (CAT – ION) is positively charged – electron removed. ANION (AN – ION) is negatively charged – electron gained. In general metals (Mg) lose electrons ---> cations (+) nonmetals (F) gain electrons ---> anions (-)

Ionic Bonds Positive cations and the negative anions are attracted to one another (remember: Opposites Attract!) Therefore, ionic compounds are usually between metals and nonmetals (opposite ends of the periodic table).

Comparison Ionic Compounds Covalent Compounds Crystalline solids (made of ions) High melting and boiling points Conduct electricity when melted Many soluble in water but not in nonpolar liquid Metal and nonmetals bond Gases, liquids, or solids (made of molecules) Low melting and boiling points Poor electrical conductors in all phases Many soluble in nonpolar liquids but not in water Nonmetals bond with other nonmetals

Covalent Bond A chemical bond in which two or more electrons are shared by two atoms. How should two atoms share electrons? 7e- 7e- 8e- 8e- F F + F Lewis structure of F2 lone pairs F single covalent bond single covalent bond F

Lewis structure of water single covalent bonds 2e- 8e- 2e- H + O + H O H or Double bond – two atoms share two pairs of electrons 8e- 8e- 8e- double bonds O C or O C double bonds Triple bond – two atoms share three pairs of electrons triple bond 8e- N 8e- or N triple bond

Polarity A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment.

+ - Dipole Moment H Cl Direction of the polar bond in a molecule. Arrow points toward the more electronegative atom. H Cl + - Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem 18

Polar Covalent Bond Electrons are shared unequally A covalent bond with greater electron density around one of the two atoms resulting in partial charges (dipole) H F e- poor e- rich electron rich region F H electron poor region d+ d-

Bond Polarity HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity) Cl has a greater share in bonding electrons than does H. Cl has slight negative charge (-d) and H has slight positive charge (+ d)

Bond Polarity This is why oil and water will not mix! Oil is nonpolar, and water is polar. The two will repel each other, and so you can not dissolve one in the other

Bond Polarity “Like Dissolves Like” Polar dissolves Polar Nonpolar dissolves Nonpolar

Determining Molecular Polarity Nonpolar Molecules -Electrons are shared equally -Symmetrical electron density -Often identical atoms -Dipole moments are symmetrical and cancel out. BF3 F 23

Polar Bonds .. .. .. F O N H Cl H H H B H H F F Polar Polar Nonpolar Xe Cl C C Cl F F Cl H F F Cl H Polar Nonpolar Nonpolar Polar A molecule has a zero dipole moment because their dipoles cancel one another. 24

Hydrogen Bonding Occurs with polar structures only Includes a positive Hydrogen ion bonding directly to a negative ion Examples: H-O H-N H-F H2O DNA, RNA, and enzymes have many Hydrogen bonding sites Strongest intermolecular force 25

London Dispersion forces Also known as van der Waals bonds Occur only with nonpolar structures Weakest intermolecular force Electrostatic bonds between atoms or molecules Temporary dipole moment 26

Lewis Dot Bonding Write down examples on board

Double and even triple bonds are commonly observed for C, N, P, O, and S H2CO SO3 C2F4

1/25/10 MONDAY Bell Ringer: Pick up the Molecular Geometry packet off the front green demo table. Remember, we needs Dots candy and toothpicks if you want to perform the edible lab 

MOLECULAR GEOMETRY

VSEPR MOLECULAR GEOMETRY Valence Shell Electron Pair Repulsion theory. Molecule adopts the shape that minimizes the electron pair repulsions. VSEPR Valence Shell Electron Pair Repulsion theory. Most important factor in determining geometry is relative repulsion between electron pairs.

Some Common Geometries Linear Tetrahedral Trigonal Planar

Other VSEPR charts

Structure Determination by VSEPR Water, H2O The electron pair geometry is TETRAHEDRAL 2 bond pairs 2 lone pairs The molecular geometry is BENT.

Structure Determination by VSEPR Ammonia, NH3 The electron pair geometry is tetrahedral. The MOLECULAR GEOMETRY — the positions of the atoms — is TRIGONAL PYRAMID.