Co-Ordinate Bonds, Intermolecular Forces and Metallic Bonding

7/30/2019 Co-Ordinate Bonds, Intermolecular Forces and Metallic Bonding

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Co-ordinate Bonds,Intermolecular Forces and

Metallic Bonding

Everything you EVER

wanted to know but

were afraid to ask!


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Co-ordinate BondingAlso referred to as DATIVE bonding.

Occurs when a PAIR of electrons is donated from one atom toanother.

Only happens when an empty orbital is present(ie an electron deficient species)

Once the coordinate bond is formed, we treat it exactly the sameas a normal covalent bond.

This is how Group 13 atoms get full octets!


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Amino-BoraneHuh!?!?!?

NH3 BH3(dont worry about the name)

Draw the Lewis Structure for NH3, then for BH3

N has a fulloctet an a lonepair ofelectrons.

NH3 is an

unchargedmolecule.

B only has 6electrons, it isdeficient.

BH3 is anuncharged

molecule.

N can donate its lone

pair to B forming aco-ordinate bond.


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Amino-BoraneNow we have a new molecule with a covalent bond between N and B.

While there are formal charges on N and B, the overall charge on themolecule is neutral.

The bond formed between N and B is just as strong as any covalentbond.


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Co-ordinate BondingDraw the co-ordinate bonds between each of the following pairs:GaCl3, Cl-

H+, H2O

H+, NH3

BF3, NH3

NH3, GaCl3

PCl3, GaCl3

AlCl3, AlCl3 (to form Al2Cl6)


6/18

Intermolecular ForcesCovalent Bonds are NOT intermolecular forces. They are

INTRAMOLECULAR forces.So what are INTERMOLECULEAR Forces?

The forces of attraction/repulsion that exist between molecules.The ones we need to overcome to change the state of the

substance.

Relative Strengths of Bond Types

Ionic Covalent

Intermolecular Forces


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Van der Waals ForcesDiscovered but the Dutch physicist, Van der Waals and named in his

honor.

They are weak interactions between molecules are divided into 2basic types:

1. Dipole Dipole

When a molecule has a permanent dipole moment (molecule ispolar), the negative end of one molecule will sit closer to thepositive end of its neighbor.

2. Dispersion or London Forces (weakest of all intermolecular)

Caused by temporary shifts in electron density within amolecule. For instance the 2 e- shared in H2, located on 1 Hatom rather than the other.


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Dipole Dipole Forces

d+ d-

d+ d-

d+ d-

d+ d-

d+ d-


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Ion Dipole ForcesExist when we dissolve an ionic compound in a polar solvent, like H2O.

The d- end of H2O is attracted to a cation (+).

The d+ end of H2O is attracted to an anion (-).


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London Forces

d+ d-

2e-

d- d+

2e-

Caused by the natural vibrations of theelectrons in the bond, there is no permanentdipole moment.

The dominant intermolecular force in non-polar substances.


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Hydrogen BondingA specific case of Dipole Dipole Forces.

Occurs when H is involved in a strongly polar bond with O, N or F.

The H nucleus (just a proton) is attracted to the lone pairs of thesehighly electronegative atoms.

The result is a network of strong intermolecular interactionsbetween H atoms and available lone pairs.

Occurs extensively in H2O, NH3 and HF.

The primary reason H2O doesnt behave as almost all other

substances in the known universe.

H2O expands when it freezes everything else contracts


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Hydrogen Bonding


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Intermolecular Take-home MessageThe stronger the intermolecular interaction, the

stronger molecules are held together.

When molecules are held together more tightly, we see the evidencewhen we examine physical properties of the substance melting andboiling points increase


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Practice QuestionsFor each of the following molecules, state which intermolecularforce will be dominant. Then state which (out of each pair) shouldhave the higher melting point.

Molecule 1 DominantForce

MeltingPoint

Molecule 2 DominantForce

MeltingPoint

H2O H-Bonding 0 C H2S Dipole -82 C

HCl Dipole -114.2 C H2 London -259 C

NH3 H-bonding -78 C H2O H-bonding O C

Br2 London -7 C I2 London 114 C


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MetalsMetals, theyre an interesting bunch . . .

They play by their own set of rules, so to describe them we need totalk about METALLIC bonding.

First of all what do we know about the properties of metals?

theyre malleable and ductile

theyre electron rich (they give up their electrons to makecations)

they conduct electricity

the free flow of electrons yields many colorful solutions

theyre shiny

they conduct heat


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Metallic BondingThe Sea of Electrons Model

Due to lowelectronegativities,

low effective nuclearcharges and largediffuse orbitals,electrons can flowfreely from one atom

to the next.


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Metallic BondingThe Sea of Electrons Model

Electrons carryelectrical current,if electrons canflow freely

throughout themetal the metal willconduct electricity.


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AlloysA mix of 2 or more metals.

2 types: Substitutional and Interstitial

Fe Fe Fe

Fe Fe Fe

C C

Zn Cu Zn

Cu Zn Cu

Brass (Zn and Cu in variousproportions)

Typically Zn is put in place of a Cu

atom.

Steel (Fe and C in variousproportions)

C fills in the holes between the Fe

atoms.

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Co-Ordinate Bonds, Intermolecular Forces and Metallic Bonding