Date post: | 04-Jan-2016 |
Category: |
Documents |
Upload: | rhoda-booker |
View: | 221 times |
Download: | 0 times |
Chapter 8Covalent Bonding
Covalent bonding …….Covalent bonding …….
• Usually forms between two nonmetals (takers)
• Neither want to give up their electrons but are willing to share electrons
Exception: Hydrogen Exception: Hydrogen
Hydrogen and a nonmetal …..neither wants to give up their electrons and neither has enough pull to take the
other’s so they share a pair of electrons
•Hydrogen has one electron, but only needs one more to be “happy”
In a covalent bond the…In a covalent bond the…
-shared electrons are attracted to adjacent nuclei
+ +
Covalent BondingCovalent Bonding
Covalent Bonds form molecules
(* remember: Ionic Compounds form formula units)
Molecule = smallest part of a covalent compound
That’s That’s why…….Covalent why…….Covalent
compounds are also compounds are also called called molecularmolecular
compoundscompounds
Binary (2-element) compounds
-similar to ionic, but indicate the number of atoms using prefixes
Naming Covalent Naming Covalent CompoundsCompounds
Prefix Meaning
Mono- 1
Di- 2
Tri- 3
Tetra- 4
Penta- 5
Hexa- 6
Hepta- 7
Octa- 8
Nona 9
Deca- 10
-if only 1 atom of 1st element, then no prefix is used
Ex.
COCarbon monoxide
CO2
Carbon dioxide
-if more than 1 atom of 1st element, then use prefix
N2O4
Dinitrogen tetraoxide
Ws. Naming Molecular Compounds
Ws. Name the following Molecular Compounds
Hydrogen Compounds can form Acids
• Remember…..Hydrogen is the exception to most rules
• Hydrogen has 1 electron but only needs 1 more to be happy so it acts like a nonmetal
• Hydrogen doesn’t want to give up it’s one electron but it is willing to share it.
• When hydrogen combines with an anion a covalent compound is formed
When these compounds are dissolved in water…..
…..they become acids.
What makes them an acid?
• Hydronium ions are formed
•Start with ionic compound name.
•Then follow the 3 rules
How to Name AcidsHow to Name Acids
Naming AcidsNaming AcidsRule #1 (Binary Acids)Rule #1 (Binary Acids)
• When anion ends in “ide”, the acid name begins with “hydro” and then ends in “ic”, then “acid”
• Ex. Hydrogen chloride (HCl)= hydrochloric acid Hydrogen sulfide (H2S) =hydrosulfuric acid
Naming AcidsNaming AcidsRule #2 (Tertiary Acids)Rule #2 (Tertiary Acids)
• If anion ends in “ate”, the acid name is the stem of the anion with the suffix “-ic” followed by the word “acid”
• Ex. Hydrogen nitrate (HNO3) = nitric acid
Naming AcidsNaming AcidsRule #3 (Tertiary Acids)Rule #3 (Tertiary Acids)
•When anion ends in “ite” , the acid name is the stem of the anion with suffix “-ous” followed by the word “acid”
•Ex. Hydrogen sulfite (H2SO3) = sulfurous acid
Ws. Name the Following Acids
Ws. Formula Writing
MoleculeMolecule
• Ex. CO H2O
1 molecule of carbon monoxide
1 molecule of water
Coefficient – the # of molecules or # of formula units .
H2O
4 molecules of water
How many molecules of How many molecules of water???water???
4
The number covalent bonds The number covalent bonds that will form depends on the that will form depends on the
# of valence electrons# of valence electrons
*Remember each atom is trying to achieve noble gas configuration (full outer shell)
7 valence electrons wants to share 1 pair
6 valence electrons wants to share 2 pair
5 valence electrons wants to share 3 pair
Chlorine atoms each have 7
valence electrons
….they each want one more so they will share one pair of electrons
Formation of Bonds
Single Covalent BondsSingle Covalent Bonds – 1 shared – 1 shared pair of electronspair of electrons
Cl2
Single bond- 1 shared pair of Single bond- 1 shared pair of electronselectrons
F and F F F
Double bond-2 shared pairs of Double bond-2 shared pairs of electronselectrons
O and O O O
Triple bond-3 shared pairs of electronsTriple bond-3 shared pairs of electrons
N and N N N
-you show the shared pair(s) of electrons between symbolsEx. Cl2
Lewis Dot Diagram of Lewis Dot Diagram of Covalent CompoundsCovalent Compounds
Cl Cl
Structural FormulasStructural Formulas •Each pair of shared electrons is
shown as a dash( - )•Ex. Cl2
Cl Cl Cl-ClLewis Dot Diagram Structural Formula
*Remember hydrogen only needs to share one pair
Be Be carefulcareful with with Hydrogen (HHydrogen (H22))
Hydrogen (HHydrogen (H22))
H-H
Diatomic Diatomic MoleculesMolecules• Two different atoms covalently
bonded
• Ex. CO OH-
Diatomic Diatomic ElementsElements
Ex.
Cl and Cl
Cl Cl
-when atoms of same element covalently bond
Diatomic Diatomic ElementsElements-elements that exist in pairs when not bonded to other atoms
(“BrINClHOF”)Br2 bromine
I2 iodineN2 nitrogenCl2 chlorineH2 hydrogenO2 oxygenF2 fluorine
More examples of More examples of singlesingle covalent bonds…covalent bonds…
Water HWater H22OO(2 single covalent
bonds)
HO
H
Hydrogen and chlorineHydrogen and chlorine
H-Cl
Methane CHMethane CH4 4
( 4 single covalent bonds)( 4 single covalent bonds)
H
H C H
H
PClPCl3 3 Phosphorus Phosphorus trichloridetrichloride
( 3 single covalent bonds)( 3 single covalent bonds)
Cl P Cl
Cl
Double BondsDouble Bonds
O O
Lewis Dot Diagram of carbon Lewis Dot Diagram of carbon dioxidedioxide
O C O
Carbon dioxideCarbon dioxide
O C O
Triple bondsTriple bonds
N N
Coordinate Coordinate Covalent BondsCovalent Bonds
• A coordinate covalent bond is formed when one atom donates both electrons to be shared.
Ammonium NHAmmonium NH44++
N H
H
H H
Ammonia NH3Hydrogen
Coordinate covalent bond
In coordinate bond structural In coordinate bond structural formula……formula……
An arrow points from the atom donating the pair of electrons toward the atom receiving them.
N HH
H
H
When drawing electron dot diagrams……..
•if an atom is “short” 2 electrons – try a coordinate covalent bond
H3(PO4)
H3(PO4)
P O
O
O
OH
H H
Coordinate covalent bond
Bond PolarityBond Polarity•Nonpolar - When bonding electrons
are equally shared (same electronegativity)
• Ex. Diatomic elements
•Polar – When one atom has higher electronegativity ( attractive force) and pulls electron closer to it. It gains a slight negative charge and the other atom gains a slight positive charge
• Ex. H2O
Ws. What is Electronegativity?
.4 and below Nonpolar covalent
Between .4 to 2.0 Polar covalent
Greater than 2.0 ionic
• If the difference is….. the type of bond will be..
Electronegativity Differences !!!!!Electronegativity Differences !!!!!
Describing each bond in the molecule as ….
•Even pull= NonpolarUneven pull = polarStrong uneven pull = ionic
Showing polarity of individual bonds
Use differences in electronegativitiesIndicated with δ ( lower case Greek letter delta) and charge.
Overall polarity of Overall polarity of MoleculesMolecules
equals the sum of all the bond polarities
The arrow points to the atom with the higher electronegativity
Symmetry in MoleculesSymmetry in Molecules• Symmetrical molecules are
usually nonpolar. Polar bonds cancel each other out
• Ex. CO2
Carbon TetrachlorideCarbon Tetrachloride
Bonds can be polar, yet Bonds can be polar, yet overall molecular polarity is overall molecular polarity is
nonpolarnonpolar
Asymmetrical Asymmetrical MoleculesMolecules
• Asymmetrical molecules are polar if there are polar bonds in the structure.
• Ex. H2O
Polarity of WaterPolarity of Water
HH
O
δ - δ -
δ + δ +
VSEPR TheoryVSEPR Theory•Valence shell electron-pair repulsion theory
• Because electron pairs repel, molecules adjust shapes so that pairs are as far away from each other as possible
Domains
• Single bond • Double bond• Triple bond• Lone unshared pair
The # of Electron Domains The # of Electron Domains determines the Basic Electron determines the Basic Electron
Domain shapeDomain shape
• Linear – 1 or 2 domains• Trigonal Planar – 3 domains• Tetrahedral – 4 domains• Trigonal bipyramidal – 5 domains• Octrahedral – 6 domains
Linear
Trigonal Planar ( flat)
Tetrahedral
Trigonal bipyramidal
Octahedral
Determining the Electron Domain Shape
• Count up all valence electrons• Start with central atom (C, or Lowest EN, never H)• Place other atoms around with maximum repulsion• Put 8 electrons around outside atoms• Any extra electrons go around the central atom• Count the number of domains to determine the
basic shape
• **** some compounds do NOT follow the octet rule
Let’s try some• CS2
• BeH2
• CO2
• CH4
• CCl4• NO3
-
• NH4+
• SiF4
• SF4
Molecular geometry
• Shapes are altered if there are non- bonding pairs of electrons
surrounding the central atom
Bent – can be formed from a trigonal planar or tetrahedral
Ex. H2O
Ex. SO2
Trigonal Pyramidal- can be formed from a tetrahedral
Ex. NH3
Ws. Electron Domain and Molecular Geometries
Structures and ModelsStructures and Models
Covalent Bonding: Molecular Model
Building Lab
Model Colors
• Black – Carbon family• Blue – Nitrogen family• Red - Oxygen family• Green or Purple - Halogens• Yellow - Hydrogen
• Use sticks to show single bonds
• Use springs to show multiple bonds
Formula Electron domain shape/
Molecular shape
Lewis Dot diagram * be careful of shape
Single, double or triple bond ( list each bond
EN Difference- list for for each bond
Bond Type ( polar or nonpolar –list for each bond)
Polarity of Molecule (polar or nonpolar)
H2
EA=D=NBD=BD=
Cl2
EA=D=NBD=BD=
EA= valenceelectrons available D = electron domains
NBD= non-bonding domains BD= bonding domains
Electron –Domain Basic Bond Shapes
• Linear
• Bent
• Trigonal Planar
• Trigonal Pyramidal
• Tetrahedral
Hints for Lab
Start with Central Atom
• If it has carbon, use “C” as central atom
• If no carbon, use single atom or atom with lowest EN as central atom
• Never put hydrogen as central atom
Hints about the Acids
• Do polyatomic ion groups first, then add the hydrogens
• Use single atom, except Hydrogen, as central atom
• Usually contain coordinate covalent bonds
Last Hint !!!!
• If an atom is “short” 2 electrons – try a coordinate covalent bond
H2(CO3)
CO
O
ODouble bond
H H
H3(PO4)
P O
O
O
OH
H H
Coordinate covalent bond
H2(SO4)
S
O
OO
O
H
H
Coordinate covalent bonds
H(NO3)
N OO
OH
Coordinate covalent bond
Properties of Properties of Covalent Covalent
CompoundsCompounds• Low melting points (usually below
300oC) • Boiling points usually lower than
ionic compounds• Many are liquids or gases at room
temperature• High to low solubility• Poor to non-conducting
Covalent Compounds form Covalent Compounds form Network SolidsNetwork Solids
• Most covalently bonds substances melt easily because you just have to break the weak attractions between molecule and molecule
• Ex. Ice – Water– Sugar (C12H22O11)
Covalent crystalsCovalent crystals
• If covalent compound forms crystals (repeating pattern)……..
• Requires a lot of energy to break all the covalent bonds
• Have high melting points• Ex. diamonds
A diamond ( pure carbon)
Solubility of Solubility of Covalent Covalent
CompoundsCompounds•“Like dissolves Like”•Polar compounds will
dissolve in polar solvents•Nonpolar compounds will
dissolve in nonpolar solvents
Why don’t water and oil mix?
-Water is polar, oil is nonpolar.
-Water is more attracted to itself than to the oil.
Why do detergents cause water and oil to mix?-detergents are long molecules with one polar and one nonpolar end.
-the water is attracted to the polar end and the oil is attracted to the nonpolar end.
Soap and DetergentSoap and DetergentNonpolar end –attracts nonpolar oil or grease
Polar end –attracts (polar)water
Chapter ReviewCovalent Bonding
Ionic vs. CovalentElectrons transfer Electrons shared
Metal and Non metal Nonmetal and Nonmetal
Formula units molecules
No prefixes in names Prefixes in names
Neutral compound Neutral compound
Called salts If starts with “H” it could be an acid when dissolved in H2O
High melting points, easily dissolved and conduct when dissolved
Low melting points, not easy to dissolve, don’t conduct electricity
Ws. Bond Prediction
Ws.Naming Compounds
Ws. Name the Following Compounds
Ws. Naming Compounds Reference Sheet
Diatomics = 2 atoms of same element bonded
to each other
BrINClHOF
Diatomic element is linear and Nonpolar
Covalent Bonds – 4 Types• Single- 1 shared pair of electrons
(1 from each atom)
• Double – 2 shared pairs of electrons (two from each atom)
• Triple- 3 shared pairs of electrons, (three from each atom)
• Coordinate covalent – both electrons of shared pair come from 1 atom
Structural FormulaStructural Formula- shows arrangement of
bonds• Cl Cl single• O O double• N N triple• C O coordinate covalent
Electron Dot Diagrams
• Every atom MUST have 8 electrons drawn around it except “H”.
• “H” needs 2 electrons
Polar vs. Nonpolar – depends on EN
( electronegativity) difference
• Nonpolar – shared evenly – EN difference below .4
• Polar – shared unevenly – EN .4 – 2.0
• Ionic – pulls electron off of atom. EN above 2.0
Polarity of Bond
•Depends on electronegativity difference
Polarity of Molecule
• Look at symmetry, then polarity of the bonds
Know how to name ionic compounds, covalent compounds and acids
The End