C OVALENT C OMPOUNDS

1. Usually soft and squishy 2. Not soluble in water 3. Does not conduct electricity 4. Low melting points 5. Low boiling points

T WO T YPES OF B ONDS  Ionic: Electrons are transferred  Covalent: Electrons are shared  Non-polar covalent: equally shared  Polar Covalent: unevenly shared

N AMING C OVALENT C OMPOUNDS

NAMING COMPOUNDS Nonmetal – Nonmetal USE PREFIXES! 1. Change the ending of the second word to -ide 2. No mono on the first word 3. Drop any double vowels

C OVALENT P REFIXES Number of AtomsPrefix 1Mono- 2Di- 3Tri- 4Tetra- 5Penta- 6Hexa- 7Hepta- 8Octa- 9Nona- 10Deca-

THE PREFIX TELLS YOU HOW MANY ATOMS YOU HAVE! NO CRISS CROSS!!!!

E XAMPLES 1. CO 2. CO 2 3. SO 2 4. SO 3 5. N 2 H 4 6. N 2 O 3 1.Carbon Monoxide 2.Carbon Dioxide 3.Sulfur Dioxide 4.Sulfur Trioxide 5.Dinitrogen Tetrahydride 6.Dinitrogen Trioxide

E XAMPLES 1. disilicon hexafluoride 2. tricarbon octachloride 3. phosphorus pentabromide 4. nitrogen monoxide 5. selenium difluoride 6. dihydrogen monoxide 1.Si 2 F 6 2.C 2 Cl 8 3.PBr 5 4.NO 5.SeF 2 6.H 2 O

EMPIRICAL AND MOLECULAR FORMULAS

Define Empirical Formula: A chemical formula that gives the simplest whole-number ratio of the elements in the formula. Which of the following is an empirical formula? CO 2 C 2 O 4 Fe 2 Cl 6 FeCl 3

Define Molecular Formula: A chemical formula that gives the actual number of the elements in the molecular compound. For the following molecular formulas, write the empirical formula: Molecular: Empirical: C 2 H 4 C 6 H 12 O 6 C 9 H 21 O 6 N 3

L EWIS S TRUCTURES

L EWIS S TRUCTURES FOR C OMPOUNDS  The pair of dots between two symbols represents the shared pair.  How many shared pairs does each fluorine have below?  An unshared pair, also called a lone pair, is a pair of electrons that is not involved in bonding and that belongs exclusively to one atom.

L EWIS S TRUCTURES  The shared pair of electrons is often replaced by a long dash. Each dash represents TWO electrons

FF + 7e - FF 8e - F F F F Lewis structure of F 2 lone pairs single covalent bond W HY SHOULD TWO ATOMS SHARE ELECTRONS ? To get a valence of 8 electrons!

M ULTIPLE C OVALENT B ONDS  double bond : covalent bond in which two pairs of electrons are shared between two atoms  shown by two side-by-side pairs of dots or by two parallel dashes

M ULTIPLE C OVALENT B ONDS  triple bond : covalent bond in which three pairs of electrons are shared between two atoms  shown by three side-by-side pairs of dots or by three parallel dashes

S TEPS FOR D RAWING L EWIS S TRUCTURES 1. Draw the Lewis Dot diagram for each individual atom 2. Count up the number of valence electrons 3. Connect the atoms together to pair up the electrons (put atoms that can make the most connections in the center) 4. Once all electrons are paired, recount electrons to double check total valence

P RACTICE Draw the Lewis Structure for HBr 1. HBr = 8 3. H — Br = 8

B OND P OLARITY

Which element is the most electronegative? H F Fluorine - Has 7 valence e - and wants 8 ability of an atom to attract electrons R EVIEW : W HAT IS ELECTRONEGATIVITY ?

H F F H electron rich region electron poor region e - rich e - poor ++ -- P OLAR BOND : covalent bond with greater electron density around one of the two atoms

Nonpolar Covalent share e - Polar Covalent partial transfer of e - Ionic transfer e - Increasing difference in electronegativity Electronegativity Difference Bond Type 0 to 0.3Nonpolar Covalent 0.4 to 1.6Polar Covalent  1.7 Ionic W HAT TYPE OF B OND IS IT ?

Classify the following bonds as ionic, polar covalent,or covalent: Cs – 0.7Cl – – 0.7 = 2.3Ionic H – 2.1S – – 2.1 = 0.4Polar Covalent Cl – 3.0N – – 3.0 = 0Nonpolar Covalent Cs to Cl H to S Cl to N

I NTERMOLECULAR F ORCES

Intermolecular forces: attractive forces between molecules. Intramolecular forces: attractive forces within a molecule (the bonds) intramolecular forces are much stronger than intermolecular forces Intramolecular Forces Intermolecular Forces

D IPOLES  What is a dipole?  A polar molecule  Uneven sharing of electrons so there is a separation of charge

D IPOLE -D IPOLE F ORCES  Attraction between two polar molecules — + — +

H YDROGEN B ONDING  Special type of Dipole – Dipole  Attraction between: Hydrogen and Nitrogen/Oxygen/Fluorine

D IPOLE – I NDUCED D IPOLE  Attraction between one polar and one nonpolar molecule — + — + — + Electrons shift toward positive end of dipole

L ONDON D ISPERSION F ORCES  Attraction between two nonpolar molecules — + — + Electrons become uneven and form a dipole

S TRENGTH OF IMF  Hydrogen Bond  Dipole – Dipole  Dipole – Induced Dipole  London Dispersion Forces strongest weakest

W HAT DOES IMF EFFECT ?  Viscosity  Surface Tension  Cohesion/Adhesion  Boiling Point

Stronger IMF  Higher Viscosity V ISCOSITY  Measures a fluid’s resistance to flow

Stronger IMF  Higher Surface Tension S URFACE T ENSION  result of an imbalance of forces at the surface of a liquid.

Adhesion Cohesion A DHESION AND C OHESION  Cohesion: intermolecular attraction between like molecules  Adhesion: intermolecular attraction between unlike molecules

B OILING P OINT  Point at which liquid particles escape the surface of the liquid into the gas phase Stronger IMF  Higher Boiling Point