BONDING AND GEOMETRY Unit 8 Chemistry. ATOMS AND IONS REVIEW Atoms are neutral They have the same number of protons and electrons Number of positives

BONDING AND BONDING AND GEOMETRYGEOMETRYUnit 8Unit 8

ChemistryChemistry

ATOMS AND IONS ATOMS AND IONS REVIEWREVIEW

Atoms are neutralAtoms are neutral They have the same number of protons and electronsThey have the same number of protons and electrons

Number of positives = number of negativesNumber of positives = number of negatives Example: NaExample: Na 11 protons, 11 electrons 11 protons, 11 electrons 11 – 11 = 0 11 – 11 = 0

Ions have a chargeIons have a charge They have a different number of protons and electronsThey have a different number of protons and electrons Example: NaExample: Na+1+111 protons, 10 electrons11 protons, 10 electrons 11 – 10 = +1 11 – 10 = +1 If an atom GAINS an electron If an atom GAINS an electron becomes negatively becomes negatively

charged charged ANION ANION If an atom LOSES an electron If an atom LOSES an electron becomes positively becomes positively

charged charged CATION CATION

TYPES OF BONDSTYPES OF BONDS

Bonding occurs because every element is Bonding occurs because every element is either trying to get to 0 electrons in the valence either trying to get to 0 electrons in the valence or 8 electrons in the valence (zero and 8 are or 8 electrons in the valence (zero and 8 are both stable)both stable) Valence is the outer electron shell—place where Valence is the outer electron shell—place where

bonding occursbonding occurs Ionic – Bonding between a metal and a Ionic – Bonding between a metal and a

nonmetalnonmetal Metallic – Bonding between two metalsMetallic – Bonding between two metals Covalent – Bonding between two nonmetalsCovalent – Bonding between two nonmetals

IONIC BONDINGIONIC BONDING

Very stable and strongVery stable and strong Strongest possible bondStrongest possible bond Requires a large amount of energy to break an Requires a large amount of energy to break an

ionic bondionic bond Forms compounds known as “ionic Forms compounds known as “ionic

compounds”compounds” All ionic compounds will dissolve in water and All ionic compounds will dissolve in water and

carry a current (electrolyte)carry a current (electrolyte) Generally have high melting and boiling pointsGenerally have high melting and boiling points Compounds are generally hard and brittleCompounds are generally hard and brittle

METALLIC BONDINGMETALLIC BONDING

Metal atoms are pieces of metal that consist of closely Metal atoms are pieces of metal that consist of closely packed cations (positively ions)packed cations (positively ions) Cations are surrounded by mobile valence electrons that are Cations are surrounded by mobile valence electrons that are

free to drift from one part of the metal to anotherfree to drift from one part of the metal to another Metal atoms are arranged in very compact and orderly Metal atoms are arranged in very compact and orderly

(crystalline) patterns(crystalline) patterns Metallic bonding is the electrostatic attraction between Metallic bonding is the electrostatic attraction between

conduction electrons, and the metallic ions within the conduction electrons, and the metallic ions within the metals, because it involves the sharing of free metals, because it involves the sharing of free electrons among a lattice of positively-charged metal electrons among a lattice of positively-charged metal ions ions Occurs between 2 or more metalsOccurs between 2 or more metals Result of the attraction of free floating valence electrons for the Result of the attraction of free floating valence electrons for the

positive ion positive ion These bonds hold metals togetherThese bonds hold metals together

COVALENT BONDINGCOVALENT BONDING

Covalent:Covalent: Covalent bonds are when atoms SHARE Covalent bonds are when atoms SHARE

VALENCE electronsVALENCE electrons

A covalent compound is called a A covalent compound is called a moleculemolecule

Covalent bond ALWAYS occurs between Covalent bond ALWAYS occurs between 2 nonmetals2 nonmetals

TYPES OF COVALENT BONDSTYPES OF COVALENT BONDS

Single BondSingle Bond Covalent bond where one pair of electrons (2 Covalent bond where one pair of electrons (2

electrons total) are shared between 2 atomselectrons total) are shared between 2 atoms Atoms share electrons so that each has a full octet Atoms share electrons so that each has a full octet

(8 valence)(8 valence) Electrons that are shared count as valence Electrons that are shared count as valence

electrons for both atomselectrons for both atoms ExamplesExamples

ClCl22


Double BondsDouble Bonds Bond in which two pairs of electrons (4 Bond in which two pairs of electrons (4

electrons total) are shared between 2 atomselectrons total) are shared between 2 atoms ExamplesExamples

OO22

Triple BondsTriple Bonds Bond in which 3 pairs of electrons (6 total Bond in which 3 pairs of electrons (6 total

electrons) are shared between atomselectrons) are shared between atoms ExamplesExamples

NN22


Electron PairsElectron Pairs Electron pairs involved in the actual bond are called Electron pairs involved in the actual bond are called

BONDING PAIR or SHARED PAIR electronsBONDING PAIR or SHARED PAIR electrons Electrons not involved in the actual bond, those Electrons not involved in the actual bond, those

surrounding the rest of each element are called surrounding the rest of each element are called LONE PAIR electronsLONE PAIR electrons

POLAR BONDS AND POLAR BONDS AND MOLECULESMOLECULES

Covalent bonds are formed by sharing Covalent bonds are formed by sharing electrons between two atomselectrons between two atoms

The bonding pair of electrons is shared The bonding pair of electrons is shared between both elements, but each atom is between both elements, but each atom is tugging on the bonding pairtugging on the bonding pair When atoms in a molecule are the same (diatomic) When atoms in a molecule are the same (diatomic)

the bonding pair is shared equallythe bonding pair is shared equallythis bond is this bond is called non polar covalentcalled non polar covalent

When atoms in a molecule are different, the bonding When atoms in a molecule are different, the bonding pair of electrons are not shared equallypair of electrons are not shared equallythis is this is called a polar covalent bondcalled a polar covalent bond


Why is the bonding pair not shared Why is the bonding pair not shared equally?equally? The answer lies within electronegativityThe answer lies within electronegativity

One of the elements is more electronegative than One of the elements is more electronegative than the other and therefore has a greater desire for the other and therefore has a greater desire for the shared pairthe shared pair

The MORE electronegative element tends to pull The MORE electronegative element tends to pull the electrons closer and thus has a slightly the electrons closer and thus has a slightly negative charge negative charge

The LESS electronegative element has a slightly The LESS electronegative element has a slightly positive charge since the shared pair is being positive charge since the shared pair is being pulled awaypulled away


Polar MoleculesPolar Molecules Molecule in which one end of the molecule is Molecule in which one end of the molecule is

slightly negative and the other end is slightly slightly negative and the other end is slightly positive positive

Just because a molecule contains a polar Just because a molecule contains a polar bond DOES NOT mean the entire molecule bond DOES NOT mean the entire molecule is polaris polar

The effect of polar bonds on the polarity of The effect of polar bonds on the polarity of an entire molecule depends on the shape of an entire molecule depends on the shape of the molecule and the orientation of the polar the molecule and the orientation of the polar bondsbonds


Example: COExample: CO22 O = C = OO = C = O

Carbon and Oxygen lie along the same axis. Carbon and Oxygen lie along the same axis. Bond polarities are going to cancel out Bond polarities are going to cancel out

because they are in opposite directionsbecause they are in opposite directions Carbon dioxide is a nonpolar molecule even Carbon dioxide is a nonpolar molecule even

though there are two polar bonds presentthough there are two polar bonds present Would cancel out if the polarities moved towards Would cancel out if the polarities moved towards

each other as welleach other as well When polarities cancel out, the molecule is non-When polarities cancel out, the molecule is non-

polarpolar


Example: HExample: H22OO

INTRAMOLECULAR INTRAMOLECULAR FORCESFORCES

Intramolecular forces- (attraction is within the molecule)

Types of forces: covalent, Ionic, metallic

INTERMOLECULAR INTERMOLECULAR FORCESFORCES

Intermolecular Forces- (attraction is between molecules)

Hydrogen bonding Dipole-Dipole Bonding Dispersion (London/van der Waals)

INTRA/INTERMOLECULAR INTRA/INTERMOLECULAR FORCESFORCES

Which is a greater force: Intermolecular or intramolecular?

Rank the strength of each kind of inter and intra molecular force.

FORCES IN A MOLECULEFORCES IN A MOLECULE

Dipole-Dipole ForcesDipole-Dipole Forces Dipoles are created when equal but opposite Dipoles are created when equal but opposite

charges are separated by a short distancecharges are separated by a short distance Have to have a positive and a negative end so Have to have a positive and a negative end so

that one of the elements is pulling on the electronthat one of the elements is pulling on the electron

Only happens in polar moleculesOnly happens in polar molecules Dipole forces are extremely strong and lead Dipole forces are extremely strong and lead

to high melting and boiling pointsto high melting and boiling points


Hydrogen BondingHydrogen Bonding Very strong type of dipole forceVery strong type of dipole force Only occurs when hydrogen is covalently Only occurs when hydrogen is covalently

bonded to a highly electronegative atombonded to a highly electronegative atom Always involves hydrogenAlways involves hydrogen Example: HF, HExample: HF, H22O, NHO, NH33

FORCES IN A MOLECULEFORCES IN A MOLECULE H – bonding and boiling point

Why does boiling point increase as you go down a group?

The increase in boiling point happens because the molecules are getting The increase in boiling point happens because the molecules are getting larger with more electrons, and so dispersion forces become greaterlarger with more electrons, and so dispersion forces become greater


London Dispersion ForcesLondon Dispersion Forces Electrons are in constant motion around a Electrons are in constant motion around a

nucleusnucleus At any given time there might be more At any given time there might be more

electrons on one side of an atom than on the electrons on one side of an atom than on the otherother

For a split second, the side with more For a split second, the side with more electrons is negative, and the side with less electrons is negative, and the side with less electrons is positiveelectrons is positive


London Dispersion ForcesLondon Dispersion Forces Recall that Noble Gases have a full outer Recall that Noble Gases have a full outer

shell and you have been told they are shell and you have been told they are unreactive BUT due to London Dispersion unreactive BUT due to London Dispersion Forces, they COULD bond for an instantForces, they COULD bond for an instant Example: ArExample: Ar22

London Forces are very weakLondon Forces are very weak The smaller the mass of the atom, the The smaller the mass of the atom, the

smaller the London Forcesmaller the London Force

BOND DETAILSBOND DETAILS

TerminologyTerminology Bond strength-energy required to break a bondBond strength-energy required to break a bond Bond axis-imaginary line joining two bonded atoms Bond axis-imaginary line joining two bonded atoms

(example: C-C)(example: C-C) Bond length-the distance between two bonded Bond length-the distance between two bonded

atoms at their minimum potential enery; the average atoms at their minimum potential enery; the average distance between two bonded atomsdistance between two bonded atoms

Bond energy-energy required to break a chemical Bond energy-energy required to break a chemical bond and form neutral isolated atomsbond and form neutral isolated atoms

Chemical compound tend to form so that each Chemical compound tend to form so that each atom, by gaining, losing, or sharing electrons, atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest has an octet of electrons in its highest occupied energy leveloccupied energy level


Comparison of Bond Length/Strength for Comparison of Bond Length/Strength for Covalent Bond Types:Covalent Bond Types: Longer bond = less bond strengthLonger bond = less bond strength Rating 1-3 (with 3 as the largest and 1 as Rating 1-3 (with 3 as the largest and 1 as

the smallest)the smallest)BondBond LengthLength StrengthStrength

SingleSingle 33 11

DoubleDouble 22 22

TripleTriple 11 33


Coordinate Covalent BondsCoordinate Covalent Bonds Very rareVery rare Tend to form harmful moleculesTend to form harmful molecules Occurs when both of the bonding pair of Occurs when both of the bonding pair of

electrons in a covalent bond come from only electrons in a covalent bond come from only ONE of the atomsONE of the atoms

Example: COExample: CO


ResonanceResonance Occurs when there are more than one possible Occurs when there are more than one possible

structures for a moleculestructures for a molecule Refers to bonding in molecules or ions that cannot Refers to bonding in molecules or ions that cannot

be correctly represented by a single Lewis structurebe correctly represented by a single Lewis structure Example: COExample: CO22

To indicate resonance, a double-headed arrow is placed To indicate resonance, a double-headed arrow is placed between a molecule’s resonance structuresbetween a molecule’s resonance structures

Even though all of the structures are different, the Even though all of the structures are different, the number of bonding pair of electrons and lone pair of number of bonding pair of electrons and lone pair of electrons stay the same in each structureelectrons stay the same in each structure

VSEPR THEORYVSEPR THEORY

Valence Shell Electron Pair Repulsion Valence Shell Electron Pair Repulsion TheoryTheory

Allows us to picture molecules in 3 Allows us to picture molecules in 3 dimensionsdimensions

Centers around the fact that electrons Centers around the fact that electrons have negative charges and repel one have negative charges and repel one anotheranother

So electron pairs within a structure try to So electron pairs within a structure try to arrange themselves to be as far away arrange themselves to be as far away from other pairs as possiblefrom other pairs as possible


TetrahedralTetrahedral Central atom bonds to 4 atoms and has zero Central atom bonds to 4 atoms and has zero

lone pairslone pairs CHCH44


PyramidalPyramidal The central atom bonds to 3 atoms and has The central atom bonds to 3 atoms and has

1 lone pair of electons1 lone pair of electons NHNH33


Trigonal PlanarTrigonal Planar The central atom bonds to 3 atoms and has The central atom bonds to 3 atoms and has

zero lone pairszero lone pairs BFBF33


Bent TriatomicBent Triatomic The central atom bonds to 2 atoms and has The central atom bonds to 2 atoms and has

2 lone pair of electrons2 lone pair of electrons HH22OO


Linear TriatomicLinear Triatomic The central atom bonds to 2 atoms and has The central atom bonds to 2 atoms and has

zero lone pair of electronszero lone pair of electrons COCO22


LinearLinear One bond between 2 atomsOne bond between 2 atoms HClHCl

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BONDING AND GEOMETRY Unit 8 Chemistry. ATOMS AND IONS REVIEW Atoms are neutral They have the same number of protons and electrons Number of positives