Covalent Bonds Other Bonds James Treasury Sen. Kit Bond Bond Bond

Bonding A metal and a nonmetal form an ionic bond by the transfer of e-. Nonmetal atoms form covalent bonds by sharing e-.

Bonding A metal and a nonmetal form an ionic bond by the transfer of e-. Nonmetal atoms form covalent bonds by sharing e-. …that’s not the whole story.

Consider electronegativity

(We can also define % ionic character) Call a bond with electronegativity difference of: 0-.4 -- nonpolar covalent bond .5-1.8 -- polar covalent bond 1.9 and above -- ionic bond (We can also define % ionic character)

What kind of bond forms between chlorine and phosphorus atoms?

What kind of bond forms between chlorine and phosphorus atoms? Cl P 3.0 - 2.1=.9 This is a polar covalent bond (use an absolute value for the difference)

What kind of bond forms between these atoms? H and Cl Cl and C Cl and F F and F Na and O Mg and N Mg and Mg N and O

The Lewis Diagram Bar represents a covalent bond, 2 shared electrons Unshared pairs fill out the octets. Double and triple bars represent double and triple bonds.

Lewis diagrams Step 1: Count the total valence electrons available --use the columns of the periodic chart --negative ions have extra electrons, --positive ions are missing electrons Step 2: Count the total valence electrons needed --duet rule for hydrogen, or the --octet rule for everything else Step 3: Number of bonds = (electrons needed-electrons available) / 2 electrons per bond

Lewis diagrams Step 4: Choose the central atom (almost always the unique one), surround it with the others. Step 5: Connect with one bond to each outer atom. (PS: Recheck your formula!) Step 6: Fill in enough multiple bonds to satisfy step 3 Step 7: Draw in unshared pairs to fill valence levels.

Don’t Don’t try to figure out whose electrons are whose. Electrons are identical. Don’t string the atoms along. Put one atom in the center, unless you have 6 or more atoms. Don’t EVER put two bonds or an unshared pair on H.

Lewis diagrams Draw a Lewis diagram of hydrogen cyanide, HCN

Lewis diagrams Draw a Lewis diagram of hydrogen cyanide, HCN H C N

Try an ion. Draw a Lewis diagram for the nitrite, NO2- , ion

Lewis diagrams Draw a Lewis diagram for the nitrite, NO2- , ion [ O N O ]-

Resonance Which one is preferable? [ O N O ]-

(the double-headed arrow signifies resonance) Each is valid. The multiple bond exists in both locations. This is called resonance. [ O N O ]- (the double-headed arrow signifies resonance)

Resonance Draw three resonance structures for carbon dioxide.

Formal Charge (#valence e-) - (#bonds/2 + unshared e-) Try to minimize each. The more electronegative atom gets a more negative formal charge.

Formal Charge Draw two valid arrangements each for the atoms in: H2CO H2O2 N2O (count bonds, put them in, fill in lone pairs)

Formal Charge Which is preferable? H H O C H O C H

Formal Charge Which is preferable? H H O C H O C H

Formal Charge Choose this one! Which is preferable? H H O C H O C H

Formal Charge Which is preferable? H H O O H O O H

Formal Charge Which is preferable? H H O O H O O H

Formal Charge Choose this one! Which is preferable? H H O O H O O H

Formal Charge Which is preferable? O N N N O N

Formal Charge Which is preferable? O N N N O N -1 +1 0 or +1 -2 +1

Formal Charge Choose this one! Which is preferable? O N N N O N

Formal Charge Which is preferable? O N N O N N

Formal Charge Which is preferable? O N N O N N -1 +1 0 or 0 +1 -1

Formal Charge Choose this one! Which is preferable? O N N O N N

Coordinate covalent bonds How did this become this? C O C O

Coordinate covalent bonds How did this become this? Carbon monoxide really does have the third bond. The oxygen donates both electrons to share. This is a coordinate covalent bond C O C O C O

Coordinate covalent bonds Draw a Lewis diagram of the ozone (O3) molecule. Count the formal charge for each atom and mark a coordinate covalent bond

Coordinate covalent bonds Draw a Lewis diagram of the ozone (O3) molecule. Count the formal charge for each atom and mark a coordinate covalent bond O O O -1 +1 0

Exceptions to the octet rule Draw a Lewis diagram for the triiodide ion, I3-

Exceptions to the octet rule Draw a Lewis diagram for the triiodide ion, I3- Gadzooks! When you try to find the number of bonds, (24-22)/2=1 bond. That’s not enough to tie the ion together.

Exceptions to the octet rule When that happens—go old school. Circle your electrons [ I I I ]-

Exceptions to the octet rule When that happens—go old school. Circle your electrons [ I I I ]-

Exceptions to the octet rule When that happens—go old school. Circle your electrons [ I I I ]- Two single bonds will satisfy the outer two iodine atoms, the middle one breaks the octet rule (with 10 electrons).

Exceptions to the octet rule Draw a Lewis diagram for XeF4 (The point here is to find out how many unshared pairs are on the central atom)

Exceptions to the octet rule Draw a Lewis diagram for XeF4 (The point here is to find out how many unshared pairs are on the central atom) F F Xe F Start here day 2 purple F

Polar bonds We use a symbol to show a polar covalent bond. The arrow points toward the more electronegative atom, the (+) end is less electronegative O H H H

Polar bonds Or, mark the molecule’s (+) and (-) parts The d is the small Greek delta. It indicates a small change. In this case, a partial charge d- O d+ H d+ H H

Three properties of polar bonds: The less electronegative end of a polar bond: d+ d- H Cl --is more positive --cannot attract the electrons as well --is farther from the shared pair of electrons Start here white day

Molecular Shapes Most molecules have a central atom that follows the octet rule. This allows the following shapes. Tetrahedral Trigonal pyramid (trigonal=having three Bent corners) Linear and Trigonal planar

Molecular Shapes Four bonds in four directions makes a tetrahedral shape

Molecular Shapes Three bonds and one lone pair in four directions makes a trigonal pyramid shape

Molecular Shapes Two bonds and two lone pairs in four directions makes a bent shape

Molecular Shapes A double bond holds two electron pairs in the same direction. With no lone pairs, this makes a trigonal planar molecule

Molecular Shapes One lone pair, with a single and a double bond gives a bent molecule.

Molecular Shapes Two double bonds, or a single and a triple makes a linear molecule

Molecular Shapes Two atoms are always in a straight line, a linear molecule.

Look for double bonds and unshared pairs If A=central atom, B=atoms bonded to it, E=e- pairs: AB4—tetrahedral (no double bonds) AB3E-trigonal pyramid AB2E2 –bent ABE3 –linear AB3— trigonal planar (one double bond) AB2E –bent ABE2—linear AB2—linear (2 doubles or 1 triple) ABE—linear (“) Look for double bonds and unshared pairs

Determine the shape of each molecule and ion on the lab that has a single central atom.

Polarity of molecules When polar bonds are not cancelled by symmetry, you get a polar molecule. A polar molecule has (+) and (-) parts. POLARITY is the first property to look for when analyzing a molecule !

Polarity CH4 has no polar bonds. It is symmetric PH3 has no polar bonds It is not symmetric CO2 has polar bonds. It is symmetric H2O has polar bonds. It is not symmetric

Polarity CH4 has no polar bonds. It is symmetric Not polar! PH3 has no polar bonds It is not symmetric CO2 has polar bonds. It is symmetric H2O has polar bonds. It is not symmetric Polar!

Mark each molecule on the lab that is polar. For those that are not polar—why not? (PS—don’t even look at the ions. If it has a whole charge, ignore the partial charges)

(Hydrogen is the only exception) Hybridization Atomic orbitals combine to form hybrid orbitals before bonding (Hydrogen is the only exception)

Before bonding The first step is a hybridization of the valence level H H H H forms… p orbitals s orbitals

Hybridization The first step is a hybridization of the valence level C H H H H The s and p orbitals hybridize to form sp3 orbitals. The sp3 designation shows one s orbital and 3 p orbitals make the new ones sp3 orbitals

Hybridization The first step is a hybridization of the valence level C H H H H The number of orbitals is preserved (4 in  4 out) sp3 orbitals

Hybridization C H H H H All four bonds are identical. Methane is a symmetrical molecule.

sp2 Hybridization When one p orbital is left out of the hybridization, it is used to make a double bond C H H O …forms…. p orbitals s orbitals

sp2 Hybridization When one p orbital is left out of the hybridization, it is used to make a double bond C H H O sp2 orbitals Unused p orbitals—will form the second bond between C and O

sp2 Hybridization When one p orbital is left out of the hybridization, it is used to make a double bond C H H O Makes the double bond!

sp2 Hybridization H C O:: Carbon & oxygen share electrons in unused p orbitals H C O:: Carbon shares electrons in sp2 orbitals

sp2 Hybridization p bond s bonds H C O:: Carbon & oxygen share electrons in unused p orbitals H C O:: Carbon shares electrons in sp2 orbitals p bond s bonds

sp Hybridization When two p orbitals are left out of the hybridization, it is used to make two double bonds, or a triple bond C O O …forms….

sp Hybridization When two p orbitals are left out of the hybridization, it is used to make two double bonds, or a triple bond C O O sp orbitals Unused p orbitals sp2 orbitals

sp Hybridization When two p orbitals are left out of the hybridization, it is used to make two double bonds, or a triple bond C O O

sp Hybridization p bonds When two p orbitals are left out of the hybridization, it is used to make two double bonds, or a triple bond C O O

sp Hybridization ::O C O:: Carbon & oxygen share electrons in unused p orbitals ::O C O:: Carbon shares electrons in sp orbitals

Look for multiple bonds! #of Multiples Bonding patterns Hybridization None AB4, AB3E, sp3 AB2E2, ABE3 One AB3, AB2E sp2 ABE2 Two AB2, ABE sp

Look for multiple bonds! #of Multiples Bonding patterns Hybridization None sp3 One sp2 Two sp

What is the hybridization of the carbon atoms in… CCl4 H2CO C2H6 C2H4 C2H2 CO CH3OH HCOOH

Molecular Orbital Theory (MOT) Overlapping s orbitals, or hybridized orbitals makes a s (sigma) bond The electron density is on the SAME line as the nuclei s* s s s

Molecular orbitals Overlapping p orbitals, makes a p (pi) bond The electron density is on a PARALLEL line to the line of the nuclei p p p + + p*

Molecular orbitals A single bond is a s bond A double bond is a s bond, and a p bond above and below the s A triple bond is a s bond, with two p bonds– above/below and front/back

For every bonding molecular orbital (s or p) an antibonding orbital is formed (s* or p*) A bond is formed when there are more bonding than antibonding electrons

VSEPR Valence Shell Electron Pair Repulsion Theory

VSEPR Valence Shell Electron Pair Repulsion Theory --pronounced “Vesper” Electron pairs repel each other. Just as it says.

VSEPR is used to predict bond angles VSEPR is used to predict bond angles. The pairs will space themselves out as far as possible. A lone pair will take as much room as a bond AND MORE! Consider sp3 hybridization

AB4—like methane. Tetrahedral 109.5o AB3E—like ammonia. Pyramidal 107o AB2E2—like water. Bent 104.5o angles --the unshared pairs force the bonds closer together—bond angles decrease

With sp2 hybridization: AB3—like carbonate. Trigonal planar: 120o AB2E—like nitrite. Bent: less than 120o ABE2—like O2(2 atoms, has to be linear)

With sp hybridization: AB2—like carbon dioxide. Linear: 180o ABE—like carbon monoxide. Linear: 180o

…but that’s just if you always follow the rules… – like the octet rule.

With dsp3 hybridization: AB5—trigonal bipyramid AB4E—seesaw AB3E2—t-shaped AB2E3—linear ABE4—linear

With d2sp3 hybridization: AB6— octahedral AB5E—square pyramid AB4E2—square planar AB3E3—t-shaped AB2E4 , ABE5—linear

What is the shape of… All of the molecules and ions on the lab? I3-, SF6, XeF4, PCl5, IF5?

Count the s and p bonds in the following molecule Count the s and p bonds in the following molecule. Label each bond as s or p H H H C C C C C H H H O

11 3 Count the s and p bonds in the following molecule. Label each bond as s or p H H H C C C C C H H H O

Determine the hybridization of the carbons and the oxygen atom

Determine the hybridization of the carbons and the oxygen atom sp sp sp3 sp2 sp3 sp2 H H H C C C C C H H H O

The molecular aufbau diagram

The molecular aufbau order s1s2s*1s2s2s2s*2s2s2px2p2py,z4p*2py,z4s*2px2…. For example: O2 has 16 electrons. Its electron configuration is: O2 s1s2s*1s2s2s2s*2s2s2px2p2py,z4p*2py,z2

The molecular aufbau order What is the electron configuration of… N2 NO Ne2 Remember: we couldn’t do a Lewis diagram with an odd number of electrons!

The molecular aufbau diagram

The molecular aufbau diagram These two can switch places—no effect on bonding, but it causes magnetic effects we can measure

The molecular aufbau diagram These two can switch places—no effect on bonding, but it causes magnetic effects we can measure

Bond order The order of a bond in a diatomic molecule is half the number of shared electrons not cancelled by antibonding electrons. Or: (number of bonding e- in the atoms-antibonding e-)/2

Bond order What is the bond order of… N2 NO Ne2 Remember: we couldn’t do a Lewis diagram with an odd number of electrons!

You will be responsible for: Writing the molecular orbital electron configuration and Calculating the bond order… …of any pair of atoms from the second period as they attempt to form a diatomic molecule.

Bond Energies The energy it takes to break a bond is the amount of energy released as the bond is formed. --measured in kJ/mol --can be used to estimate DHrxn --can be absorbed or emitted as light.

What is the DHf of NH3?

What is the DHf of NH3? Write the reaction N2 + 3H2 2NH3

What is the DHf of NH3? Count the bonds made and broken N2 + 3H2 2NH3 1 NN triple bond, 3 HH single bonds broken 6 NH single bonds made

What is the DHf of NH3? Look up bond energies, and find a total N2 + 3H2 2NH3 1 molx941kJ/mol+3 molx436kJ/mol= 2249kJ used 6 molx393 kJ/mol=2358 kJ released

What is the DHf of NH3? Find the difference, express as kJ/mol N2 + 3H2 2NH3 2358 kJ-2249kJ=109 kJ more is released, as 2mol NH3 is produced, DHf=-109kJ/2mol=-55kJ/mol

It’s an estimate. My book claims -46 kJ/mole.

What is the heat of reaction for: CH4 + O2 H2O +CO2

What is the heat of reaction for: CH4 +2O2 2H2O +CO2

What is the heat of reaction for: CH4 +2O2 2H2O +CO2 Break 2 O=O and 4 C-H Form 4 H-O and 2 C=O

What is the heat of reaction for: CH4 +2O2 2H2O +CO2 Break 2 O=O and 4 C-H =2@500 kJ + 4@393kJ=2572kJ Form 4 H-O and 2 C=O =4@464kJ + 2@799kJ= 3454 kJ

What is the heat of reaction for: CH4 +2O2 2H2O +CO2 Break 2 O=O and 4 C-H =2@500 kJ + 4@393kJ=2572kJ Form 4 H-O and 2 C=O =4@464kJ + 2@799kJ= 3454 kJ -882kJ/mol

What is the heat of reaction for: 2H2O2 2H2O +O2

Tasks

On your test, you will be asked to: Describe how and why ionization of metals and non-metals occurs Write EC’s for atoms and ions Show formation of ionic and covalent bonds by electron dot diagrams Describe metallic bonding Define and identify electrolytes

On your test, you will be asked to: Identify particles and types of substances by bonding Draw Lewis diagrams Identify shapes of molecules and ions Identify types of bonds between atoms Describe polarity

On your test, you will be asked to: Identify polar and nonpolar molecules Identify hybridizations Describe single and double bonds by MOT Estimate DHrxn by bond energies Use VSEPR to predict molecular shapes and bond angles. Calculate and justify bond orders for diatomics from the second period