chemical bonding chapter 6 general chemistry valence electrons valence electrons...
TRANSCRIPT
Chemical Bonding
Chapter 6
General Chemistry
Valence Electrons• Valence electrons _____________________________________________________________________________
– The s and p electrons in the outer energy level– Fluorine [He] 2s2 2p5 = 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
2s2 2p5
Lewis Dot (Electron Dot) Diagrams
• Lewis Dot (electron dot) diagrams ___________________________________
X
Lewis Dot Diagrams of Selected Elements
Element Valence e- Lewis dot diagram
Sodium 1 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 -787.5 kJ/mol (weaker bond)– MgO -3760 kJ/mol (stronger bond)
Crystalline structure
Ionic Bonding Lewis Dot Diagrams
Na Cl
Ionic Bonding Lewis Dot Diagrams
Na+ Cl-
Ionic Bonding Lewis Dot Diagrams
Ca2+ P 3-
Ca2+P
3-
Ca2+
Ionic Bonding Lewis Dot Diagrams
= Ca3P2Formula 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 solids @ 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…
F F
Covalent bonding• Fluorine has seven valence electrons• A second atom also has seven• By sharing electrons…• …both end with full orbitals
F F8 Valence electrons
Bonding and Nonbonding Electrons
• _______________________ are involved in a chemical bond
• ___________________________________are not involved in bonding and belong exclusively to one atom
Nonbonding electronsBonding
electrons
Diatomic Elements
• __________ pure elements that exist as pairs in nature
• Are covalently bonded– H2 N2 O2 F2 Cl2 Br2 I2
• 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 0.0-0.4)
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 2.1Cl = 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.
H Cl
Calculate Polarity of Bond
Difference in Electronegativity
Type of Bond
0.0-0.4
0.5-1.9
2.0 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: CO2
Intermolecular Forces
Intermolecular Forces
• Polar molecules, such as water (H2O) 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: H2O NH3
London Dispersion Forces
• London Dispersion Forces– Generally only significant IM force in nonpolar
molecules– Attraction between large massed atoms (that
have lots of electrons)– ______________________________________
______________________________________