1 CHEMICAL BONDING Cocaine

2 Chemical Bonding What property of atoms determines the type of bond they form?

3 Review of Chemical Bonds There are 3 forms of bonding:There are 3 forms of bonding: _________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another_________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another _________—some valence electrons shared between atoms_________—some valence electrons shared between atoms _________ – holds atoms of a metal together_________ – holds atoms of a metal together Most bonds are somewhere in between pure ionic and pure covalent.

4 Electronegativity How do you determine what type of bond is formed between two atoms? Look at the electronegativity values of the atoms. Electronegativity-the ability of an atom to attract electrons in a chemical bond.

5 The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together. In general, the farther apart 2 atoms are on the periodic table, the more polar the bond they make will be.

6 Electronegativity Difference If the difference in electronegativities is between: – 1.7 to 4.0: Ionic – 0.4 to 1.7: Polar Covalent – 0.0 to 0.4: Non-Polar Covalent Example: NaCl Na = 0.8, Cl = 3.0 Difference is 2.2, so this is an ionic bond!

7 Non Polar Bonds If the difference in electronegativity is between , the bond is nonpolar covalent. What type of compounds have nonpolar covalent bonds? Diatomic Elements: Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2 These elements do NOT exist as single atoms on their own. MEMORIZE THESE! Since the two atoms in a diatomic molecule have identical electronegativities,  EN = 0 and the bond is nonpolar covalent.

8 Bond Polarity HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity is between 0.4 and 1.7) Cl has a greater share in bonding electrons than does H. Cl has partial negative charge (-  ) and H has partial positive charge (+  )  EN = EN Cl - EN H  EN = 3.0 – 2.1  EN = 0.9 (polar covalent)

9 NONPOLAR COVALENT Nonpolar: A bond in which a pair of electrons is distributed or shared equally between two atoms

10 NONPOLAR COVALENT Completely non-polar: Nitrogen gas (N 2 ), methane gas (CH 4 ), oxygen gas (O 2 ), chlorine gas (Cl 2 ) (and homogeneous diatomic molecules such Br 2, I 2, and F 2 ), acetylene (C 2 H 2 ), carbon tetrachloride (CCl 4 ). completely canceledNote that these are all perfectly symmetrical and this is why they are non- polar. The dipole moments of any polar bonds is completely canceled out by equal and opposite dipole moments from the other bonds. Mostly non-polar: All basic hydrocarbons (such as propane, butane, pentane, hexane, cyclohexane, octane and others), oils (such as vegetable oils), fats and greases, gasoline, diethyl ether, and others

11 Examples Predict the bond type in: HCl NaCl CCl 4 NH 3

12 Dipoles Molecules that have a polar covalent character are said to have a dipole The more electronegative element pulls electrons and makes that side of the molecule more negative. Use an arrow to indicate the direction electrons are being pulled.

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

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

16 Types of intermolecular forces 1.Induced dipole or dispersion forces –Large covalent molecule shifts e- to make  - and  + and those charges are attracted –Usually non-polar

17 Types of intermolecular forces continued: 2.Dipole-dipole force: attraction between polar molecules –Stronger than induced dipole 3.Hydrogen bonding: strongest type of intermolecular force –hydrogen of 1 atom attracted to F,O,N of another atom H O H H O H

18 In Conclusion… Intermolecular forces –Hydrogen bond »Strongest bond, so higher MP and BP –Dipole-dipole »Medium, so medium MP, BP –Induced dipole (dispersion forces) »Low MP, BP The longer the C chain the higher the MP and BP

19 Last Friday’s Lab (some molecular compound info that might help)

20 -Mineral oil contains hydrocarbons (molecular compounds) that are byproducts of petroleum distillation. -Cottonseed oil is a mixture of multiple different molecular compounds. -Cola: check the ingredients and nutrition facts.

21 This comparison may help you with your lab… Ionic Bonds –Formula unit –Transfer e- –Cation and anion –Solid –High Solubility in water –High BP, MP >300C –Good conductor in solution Covalent bonds –Molecule –Share e- –Nonmetals –Solid, liquid or gas –Low solubility in water –High to Low MP, BP<300C –Poor to non-conductivity

22 What is an acid? An acid is a molecular substance that dissolves in water to produce hydrogen ions –NOTE: ALL acids contain hydrogen… BUT…Not everything with hydrogen is an acid! They are covalent compounds that separate into a cation and an anion in water (ionic tendency)

23 Naming Acids Binary acids: –The name begins with the prefix hydro- –The name is derived from the anion –The suffix –ide should be changed to –ic

24 Try two for yourself… One of the many uses for HCl is cleaning concrete, but it’s also found in your stomach…What is the name of this acid? Some wheel cleaning compounds used in carwashes contain hydrofluoric acid. What is the formula for this acid?

25 Naming Acids Polyatomic acids: –Do not use prefix hydro- –The suffix –ate should be changed to –ic –The suffix –ite should be changed to –ous He “-ate” “-ic” and got stomach “-ite” “-ous.”

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27 Don’t worry, these problems won’t corrode your brain… In addition to its many other uses, nitric acid is commonly used in the woodworking industry to artificially age pine and maple. What is the formula for this acid? What would be the name of HClO 2 H 2 CrO 4 was once widely used in the band instrument repair industry, because of its ability to “birghten” raw brass. What is the name of this acid?

28 MOLECULAR GEOMETRY

29 VSEPR VSEPR V alence S hell E lectron P air R epulsion theory.V alence S hell E lectron P air R epulsion theory. Most important factor in determining geometry is relative repulsion between electron pairs.Most important factor in determining geometry is relative repulsion between electron pairs. Molecule adopts the shape that minimizes the electron pair repulsions. MOLECULAR GEOMETRY

30 Some Common Geometries Linear Trigonal Planar Tetrahedral

31 VSEPR charts Use the Lewis structure to determine the geometry of the moleculeUse the Lewis structure to determine the geometry of the molecule Electron arrangement establishes the bond anglesElectron arrangement establishes the bond angles Molecule takes the shape of that portion of the electron arrangementMolecule takes the shape of that portion of the electron arrangement Charts look at the CENTRAL atom for all data!Charts look at the CENTRAL atom for all data! Think REGIONS OF ELECTRON DENSITY rather than bonds (for instance, a double bond would only be 1 region)Think REGIONS OF ELECTRON DENSITY rather than bonds (for instance, a double bond would only be 1 region)

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

33 Balloon Activity