Chemical Bonding Chapter 6 General Chemistry

Valence Electrons Valence electrons ______________________________ _______________________________________________ –The s and p electrons in the outer energy level –Fluorine [He] 2s 2 2p 5 = 7 valence e- The electrons responsible for the chemical properties of atoms are those in the outer energy level ________________those in the energy levels below the outer energy level 2s 2 2p 5

Lewis Dot (Electron Dot) Diagrams Lewis Dot (electron dot) diagrams ___________________________________ X

Lewis Dot Diagrams of Selected Elements ElementValence e-Lewis dot diagram Sodium1 Na Magnesium Phosphorus Chlorine

Octet Rule The octet rule: _______________________ _____________________________________ Want to achieve the e- configuration of a noble gas Why named “octet”? Exceptions?

Chemical Bonding When atoms bond, the valence electrons are redistributed to make the atom more stable _______________results from the electrical attraction between large numbers of cations and anions Covalent bonding: results from the _______ of electrons between two atoms

Ionic Bonding

Remember Ions ? Ions: charged atoms Cations: positively charged atoms –_________________________________ to create a noble gas configuration (cations) Anions: negatively charged atoms –_________________________________to create a noble gas configuration (anions)

Ionic Bonds Formed between ________________ atoms Anions and cations are held together by opposite charges The bond is formed through the transfer of electrons Ionic compounds are called ___________ Simplest ratio is called the ____________ –Example: Na + will bond with Cl - to make sodium chloride, NaCl

Electronegativity Electronegativity: reflects an atom’s ability to attract electrons in a chemical bond Metals generally have ___ electronegativity Nonmetals generally have high electronegativity

How Determine if Ionic? Ionic bonds form between 2 atoms with difference in electronegativity of 2.0 or greater

Properties of Ionic Compounds Conduct electricity in aqueous form –are __________________ High melting and boiling points Usually solids at room temperature Have ________________ Example: sodium chloride (table salt)

Lattice Energy The strength of an ionic bond compared to another ionic bond is determined by the lattice energy Lattice energy _______________________ _____________________________________ Examples: –NaCl kJ/mol (weaker bond) –MgO-3760 kJ/mol (stronger bond)

Crystalline structure

Ionic Bonding Lewis Dot Diagrams NaCl

Ionic Bonding Lewis Dot Diagrams Na + Cl -

Ionic Bonding Lewis Dot Diagrams Ca 2+ P 3- Ca 2+ P 3- Ca 2+

Ionic Bonding Lewis Dot Diagrams = Ca 3 P 2 Formula Unit

Metallic Bonding

Metallic Bonds Metallic bonding is the bonding that results from the attraction between _______________________________ _______________________________ –Bond between two metal atoms

Sea of Electrons Metals hold on to their valence electrons very weakly. Think of them as positive ions (cations) floating in a ______________ Electrons are free to move through the solid. Metals conduct electricity.

Covalent Bonding

Covalent Bonds Two nonmetals_____ electrons to achieve full octet of electrons By sharing, both atoms get to count the electrons toward a noble gas configuration. Form molecules - _____________________ ___________________

Examples of Molecules

How determine if covalent? Covalent bonds form between 2 atoms with difference in electronegativity of ________________

Properties of Covalent Compounds Do not conduct electricity in aqueous solution –Are __________________ Relatively low melting and boiling points Can be gasses, liquids or room temp –Examples: sugar, wax, carbon dioxide

Comparison of MP, BP in Ionic and Covalent Compounds

Bond Energy The strength of an covalent bond compared to another covalent bond is determined by the bond energy Bond Energy: _______________________ _____________________________________ ___________________________________ –Stronger covalent bonds have a higher bond energy

Bond Energy and Bond Length

Bond Length Bond Length: ________________________ _____________________________________ The longer the bond, the ___________ the bond energy (the ___________the bond) The shorter the bond, the ___________ the bond energy (the ___________ the bond)

Types of Covalent Bonds Single covalent Double covalent Triple covalent Share __ e- (one pair) Share __e- (two pairs) Share __e- (three pairs)

Covalent bonding Fluorine has seven valence electrons F

Covalent bonding Fluorine has seven valence electrons A second F atom also has seven By sharing electrons… FF

Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals FF 8 Valence electrons

Bonding and Nonbonding Electrons _______________________ are involved in a chemical bond ___________________________________ are not involved in bonding and belong exclusively to one atom Nonbonding electrons Bonding electrons

Diatomic Elements __________ pure elements that exist as pairs in nature Are covalently bonded –H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2 Ways to remember: –BrINClHOF –H, N, O, Halogens

Polarity

Bond Polarity Atoms of elements do not always share electrons equally ___________________unequal sharing of electrons (dif electroneg 0.5 – 1.9) ___________________equal sharing of electrons (dif electroneg )

Bond Polarity When two different atoms bond covalently, there is an unequal sharing –the more electronegative atom will have a _____________ attraction and will acquire a slightly ________charge –called a polar covalent bond or simply polar bond.

Bond Polarity Refer to Periodic Table values of Electronegativity Consider HCl H = electronegativity of 2.1 Cl = electronegativity of 3.0 –the bond is _________ –the chlorine acquires a slight negative charge, and the hydrogen a slight positive charge

Bond Polarity Only partial charges, much less than a true 1+ or 1- as in ionic bond Written as: H Cl the positive and minus signs (with the lower case delta ) denote partial charges.  

Bond Polarity Can also be shown: the arrow points to the more electronegative atom. HCl

Calculate Polarity of Bond Difference in Electronegativity Type of Bond and greater

Geometry

VSEPR Theory Valence Shell Electron Pair Repulsion Theory ___________________________________ ___________________________________ Allows chemists to predict shapes of simple molecules

Predict shape and polarity Shape affects polarity of molecule Even though atoms may have dif electroneg > 0.5, the shape may cancel out the effects Example: CO 2

Intermolecular Forces

Polar molecules, such as water (H 2 O) attract other polar molecules. The forces of attraction between molecules are known as _______________________ –Stronger IM Forces result in ________ MP, BP (solids and liquids) –Weaker IM Force result in __________MP, BP (liquids, gases)

Types of Intermolecular Forces Dipole-dipole forces Hydrogen bonding London Dispersion Forces

Dipole-Dipole Dipole-dipole forces –Attractions between ________________ –Example: BrF

Hydrogen Bonding Hydrogen bonding –Is a special type of dipole-dipole attraction –Not really a “bond” but a stronger attraction –______________________________________ ______________________________________ –Example: H 2 O NH 3

London Dispersion Forces –Generally only significant IM force in nonpolar molecules –Attraction between large massed atoms (that have lots of electrons) –______________________________________ ______________________________________