Forces Of Attraction
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Transcript of Forces Of Attraction
Forces of AttractionForces of Attraction
IntroductionIntroduction
Atoms aggregate to form molecules and Atoms aggregate to form molecules and latticelattice
Molecules aggregate to form condensed Molecules aggregate to form condensed phases of mattephases of matte
Aggregation of atoms, appositively Aggregation of atoms, appositively charged ions and molecules is a charged ions and molecules is a
consequence ofconsequence of
Electrical forces exerted on the electrons Electrical forces exerted on the electrons of one particle by the nucleus (or nuclei) of of one particle by the nucleus (or nuclei) of the otherthe other
www.wpi.edu/academics/Depts/chemistry/www.wpi.edu/academics/Depts/chemistry/course/general/concept6.html.course/general/concept6.html.
Two broad categories of forces of Two broad categories of forces of attractionattraction
Intramolecular- forces that exist within Intramolecular- forces that exist within molecules or fundamental/formula unitsmolecules or fundamental/formula units
(forces that hold atoms or ions in a (forces that hold atoms or ions in a compound)compound)
Intermolecular- forces of attraction that Intermolecular- forces of attraction that exist between the molecules in a exist between the molecules in a compoundcompound
Intramolecular ForcesIntramolecular Forces
Three typesThree types
1.1. Ionic Ionic
2.2. CovalentCovalent
3.3. metallicmetallic
Ionic or Electrovalent BondIonic or Electrovalent Bond
Electrostatic force of attraction between Electrostatic force of attraction between ions of opposite chargeions of opposite charge
Ions are formed from atoms as a result of Ions are formed from atoms as a result of electron transfer from one atom to anotherelectron transfer from one atom to another
Formed as a result of a large difference in Formed as a result of a large difference in electronegativity of atomselectronegativity of atoms
Formed between metals and non-metalsFormed between metals and non-metals
Electronegativity- the ability of an atom Electronegativity- the ability of an atom to attract (pull) electrons to itself.to attract (pull) electrons to itself.
Electrostatic force depends on the charge Electrostatic force depends on the charge on the ions.on the ions.
PropertiesProperties
Crystalline solids- rigidity and strengthCrystalline solids- rigidity and strength
High melting and boiling pointsHigh melting and boiling points
Conduct electricity in molten and aqueous Conduct electricity in molten and aqueous statestate
They are hardThey are hard
They are brittleThey are brittle
Soluble in polar solvents such as water Soluble in polar solvents such as water (solute-solvent interactions)(solute-solvent interactions)
Covalent BondsCovalent Bonds
Formed between atoms with a small difference Formed between atoms with a small difference in electronegativityin electronegativity
Formed by the overlapping of atomic orbital.Formed by the overlapping of atomic orbital.
Molecular orbital resultMolecular orbital result
Electrons are shared between nuclei of the two Electrons are shared between nuclei of the two atomsatoms
The attraction between the shared electrons and The attraction between the shared electrons and the nuclei that holds the molecule togetherthe nuclei that holds the molecule together
Two types of bonds are formed Two types of bonds are formed
1.1. Either sigma bondsEither sigma bonds
2.2. Or pi bondsOr pi bonds
Sigma bondsSigma bonds
Three possible ways for a sigma bond to Three possible ways for a sigma bond to be formedbe formed
1.1. Overlapping of two S-orbitalOverlapping of two S-orbital
2.2. Overlapping of an S and a P-orbitalOverlapping of an S and a P-orbital
3.3. Head to head overlapping of two P-Head to head overlapping of two P-orbitalorbital
Pi bondsPi bonds
The side to side overlapping of two P The side to side overlapping of two P orbital.orbital.
Electrons in this bond are delocalizedElectrons in this bond are delocalized
The electron density is above and below The electron density is above and below the plane of the sigma bond.the plane of the sigma bond.
These bonds make a compound reactive These bonds make a compound reactive
example in alkenes with the c-c double example in alkenes with the c-c double bond.bond.
Properties of Covalent CompoundsProperties of Covalent Compounds
Liquids and gases at room temperatureLiquids and gases at room temperature
Relatively low boiling point.Relatively low boiling point.
Do not conduct electricityDo not conduct electricity
Insoluble in polar solventInsoluble in polar solvent
Soluble in non-polar solventSoluble in non-polar solvent
Dative (Coordinate) covalent BondDative (Coordinate) covalent Bond
One atom donates both electrons to form One atom donates both electrons to form a covalent bonda covalent bond
Recall- in a normal covalent bond each Recall- in a normal covalent bond each atom donates an electron to be shared.atom donates an electron to be shared.
The atom donating the electrons must The atom donating the electrons must have at least one lone pair of the have at least one lone pair of the electrons.electrons.
The other atom must have an available The other atom must have an available empty orbital to accommodate this empty orbital to accommodate this electron pairelectron pair
example, boron trifluoride, aluminium example, boron trifluoride, aluminium trichloride.trichloride.
can bond with say ammonia.can bond with say ammonia.
Metallic BondsMetallic Bonds
Positive ions surrounded by a sea of Positive ions surrounded by a sea of mobile (delocalized) electrons.mobile (delocalized) electrons.
Strong electrostatic force of attraction Strong electrostatic force of attraction binds the system togetherbinds the system together
Attraction between valence electrons and Attraction between valence electrons and metal ionmetal ion
What influences the strength of the What influences the strength of the bond?bond?
Availability of electronsAvailability of electrons
-- More available delocalized electrons, the More available delocalized electrons, the stronger the electrostatic attraction, the stronger the electrostatic attraction, the stronger the metallic bond.stronger the metallic bond.
Size of the charge on metal ionSize of the charge on metal ion
- Larger charge size, stronger the metallic Larger charge size, stronger the metallic bond. Explain.bond. Explain.
example Al and Naexample Al and Na
hard metal and soft metalhard metal and soft metal
Properties of metalsProperties of metals
Hardness- Hardness refers to the ability of Hardness- Hardness refers to the ability of a metal to resist abrasion, penetration, a metal to resist abrasion, penetration, cutting action, or permanent distortion cutting action, or permanent distortion
Brittleness- Brittleness is the property of a Brittleness- Brittleness is the property of a metal that allows little bending or metal that allows little bending or deformation without shattering deformation without shattering
Malleability- A metal that can be Malleability- A metal that can be hammered, rolled, or pressed into various hammered, rolled, or pressed into various shapes without cracking or breaking or shapes without cracking or breaking or other detrimental effects is said to be other detrimental effects is said to be malleable. malleable.
Ductility- Ductility is the property of a metal Ductility- Ductility is the property of a metal that permits it to be permanently drawn, that permits it to be permanently drawn, bent, or twisted into various shapes bent, or twisted into various shapes without breaking without breaking
Elasticity- Elasticity is that property that Elasticity- Elasticity is that property that enables a metal to return to its original enables a metal to return to its original shape when the force that causes the shape when the force that causes the change of shape is removed. change of shape is removed.
ToughnessToughness
DensityDensity
Fusibility Fusibility
Conductivity- Conductivity is the property Conductivity- Conductivity is the property that enables a metal to carry heat or that enables a metal to carry heat or electricity electricity
Contraction Contraction
ExpansionExpansion
Polar Covalent Bonds and Dipole Polar Covalent Bonds and Dipole MomentsMoments
Polar bonds- formed between atoms of Polar bonds- formed between atoms of different electronegativity (EN)different electronegativity (EN)- example, chlorine-carbon bond- example, chlorine-carbon bond * chlorine is more EN than carbon* chlorine is more EN than carbon * chlorine attracts the shared electron pair * chlorine attracts the shared electron pair
to itself.to itself. * C-Cl bond is polarized (delta negative * C-Cl bond is polarized (delta negative and delta positiveand delta positive
Polarized bonds have dipole moment.Polarized bonds have dipole moment.
Dipole- Dipole- separation of charge within separation of charge within moleculesmolecules
Intermolecular ForcesIntermolecular Forces
What are the forces between one What are the forces between one chlorine molecule and another?chlorine molecule and another?
Intermolecular forces-Intermolecular forces- forces between forces between molecules or ions and influence their molecules or ions and influence their properties.properties.
Molecular polarityMolecular polarity gives rise to the forces gives rise to the forces of attraction between moleculesof attraction between molecules
characteristicscharacteristics
These forces are electrical – result from These forces are electrical – result from mutual attraction or mutual repulsion.mutual attraction or mutual repulsion.
Generally very weak forces of attractionGenerally very weak forces of attraction
Responsible for the states of matterResponsible for the states of matter
Characteristic FeaturesCharacteristic Features
Attractions exerted by one molecule of a Attractions exerted by one molecule of a molecular substance on another, such as molecular substance on another, such as the force of attraction between water the force of attraction between water molecules in ice. molecules in ice.
Attractions between molecules of one Attractions between molecules of one substance and molecules of another, as substance and molecules of another, as when two liquids are mixed, or a molecular when two liquids are mixed, or a molecular solid such as sugar is dissolved in a liquid. solid such as sugar is dissolved in a liquid.
Attractions between atoms of the noble Attractions between atoms of the noble gas elements, helium through radon.gas elements, helium through radon.
Attraction between molecules of one Attraction between molecules of one substance and ions of another, as when substance and ions of another, as when an ionic compound dissolves in a liquid. an ionic compound dissolves in a liquid.
Types of I.M.FTypes of I.M.F
Ion-dipoleIon-dipole
Dipole-dipoleDipole-dipole
London dispersion forcesLondon dispersion forces
Hydrogen bondsHydrogen bonds
Ion-Dipole ForcesIon-Dipole Forces
Result from electrical interactions between Result from electrical interactions between an ion and the partial charges on a polar an ion and the partial charges on a polar molecule.molecule.
Dipolar molecule- a substance with both a Dipolar molecule- a substance with both a positive and negative endspositive and negative ends
In the presence of ions dipolar molecules In the presence of ions dipolar molecules orient themselves with positive end of orient themselves with positive end of dipole near the anion and negative end dipole near the anion and negative end near cationnear cation
Magnitude of interaction depends on Magnitude of interaction depends on charge.charge.
example: NaCl in water (ionic substance in example: NaCl in water (ionic substance in dipolar water molecules).dipolar water molecules).
Dipole-Dipole forces-Dipole-Dipole forces- Intermolecular Intermolecular forces that operate between neutral forces that operate between neutral molecules having molecular dipole molecules having molecular dipole moments are called dipole-dipole forces moments are called dipole-dipole forces
Result from interactions among dipoles on Result from interactions among dipoles on neighbouring molecules.neighbouring molecules.
The more polar the substance the , the The more polar the substance the , the greater the strength of its dipole-dipole greater the strength of its dipole-dipole interactions.interactions.
The stronger the I.M.F that must be The stronger the I.M.F that must be overcome for a substance to boil or melt.overcome for a substance to boil or melt.
Permanent DipolePermanent Dipole
Inductive Forces and DispersionInductive Forces and Dispersion
InductiveInductive forces arise from the forces arise from the distortiondistortion of the charge cloud induced by the of the charge cloud induced by the presence of another molecule nearby. presence of another molecule nearby.
Distortion arises from the electric field Distortion arises from the electric field produced by the charge distribution of the produced by the charge distribution of the nearby molecule. nearby molecule.
These forces are These forces are always attractivealways attractive but but shorter ranged than electrostatic forces. shorter ranged than electrostatic forces.
If a charged molecule (ion) induces a If a charged molecule (ion) induces a dipole moment in a nearby neutral dipole moment in a nearby neutral molecule, the two molecules will stick molecule, the two molecules will stick together, even though the neutral together, even though the neutral molecule was initially round and molecule was initially round and unchargeduncharged
Dipole-Induced DipoleDipole-Induced Dipole
What would happen if HCl is mixed with What would happen if HCl is mixed with argon, which has no dipole moment?argon, which has no dipole moment?
- The electrons on an argon atom are - The electrons on an argon atom are distributed homogeneously around the distributed homogeneously around the nucleus of the atom.nucleus of the atom.
- Electrons are in constant motion. - Electrons are in constant motion.
Argon close to a polar HCl molecule, the Argon close to a polar HCl molecule, the electrons can shift to one side of the electrons can shift to one side of the nucleus to produce a very small dipole nucleus to produce a very small dipole moment that lasts for only an instant. moment that lasts for only an instant.
Distorting the distribution of electrons Distorting the distribution of electrons around the argon atom, the polar HCl around the argon atom, the polar HCl molecule induces a small dipole moment molecule induces a small dipole moment on this atom.on this atom.
A weak dipole-induced dipole force of A weak dipole-induced dipole force of attraction between the HCl molecule and attraction between the HCl molecule and the Ar atom is createdthe Ar atom is created
Dipole-Induced DipoleDipole-Induced Dipole
Induced Dipole- Induced DipoleInduced Dipole- Induced Dipole
Some atoms are perfectly symmetrical. Some atoms are perfectly symmetrical.
No dipole existNo dipole exist
Some forces must existSome forces must exist
Atoms and Molecules such as; the noble Atoms and Molecules such as; the noble gases, the halogens etc.gases, the halogens etc.
Electrons are in constant motion.Electrons are in constant motion.
Example: Helium atomExample: Helium atom
Movement of the electrons around the Movement of the electrons around the nuclei of a pair of neighboring helium nuclei of a pair of neighboring helium atoms can become synchronized so that atoms can become synchronized so that each atom simultaneously obtains an each atom simultaneously obtains an induced dipole moment. induced dipole moment.
There are fluctuations in electron density There are fluctuations in electron density occurring constantly.occurring constantly.
Creating an induced dipole-induced dipole Creating an induced dipole-induced dipole force of attraction between pairs of atoms. force of attraction between pairs of atoms.
This force is relatively weak in helium.This force is relatively weak in helium.
Atoms or molecules become more Atoms or molecules become more polarizable as they become larger polarizable as they become larger because there are more electrons to be because there are more electrons to be polarized. polarized.
Induced Dipole- Induced DipoleInduced Dipole- Induced Dipole
Hydrogen BondingHydrogen Bonding
Hydrogen Bonding-Hydrogen Bonding- a special kind of a special kind of dipole-dipole force that occurs when a dipole-dipole force that occurs when a hydrogen atom is bonded to one of the hydrogen atom is bonded to one of the very electronegative atoms, F, O, or N. very electronegative atoms, F, O, or N.
Electronegative atom must have at least a Electronegative atom must have at least a lone pair of electronslone pair of electrons
Hydrogen BondingHydrogen Bonding
Combination of forcesCombination of forces
- normal covalent bond- normal covalent bond
- dipole-dipole interaction- dipole-dipole interaction
Hydrogen BondingHydrogen Bonding
The H-F, H-O, and H-N bonds are very The H-F, H-O, and H-N bonds are very polar, because the electronegative atom polar, because the electronegative atom draws the bonding electron pair strongly to draws the bonding electron pair strongly to itself. This leaves the hydrogen nucleus itself. This leaves the hydrogen nucleus exposed exposed
Hydrogen Bonding in waterHydrogen Bonding in water
Summary I.M.FSummary I.M.F
Summary of Forces of AttractionSummary of Forces of Attraction
http://www.chem.ufl.edu/~itl/2045/http://www.chem.ufl.edu/~itl/2045/lectures/lec_g.htmllectures/lec_g.html