unit 3 periodic trends, electron configurations, and bonding

UNIT 3

PERIODIC TRENDS, ELECTRON

CONFIGURATIONS, AND BONDING

Periodic Table TrendsPeriodic Table Trends

Periodic LawPeriodic Law““When arranged by increasing atomic number, the chemical When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and elements display a regular and repeating pattern of chemical and physical properties.”physical properties.”Atoms with similar properties appear in groups or families (vertical Atoms with similar properties appear in groups or families (vertical columns) on the periodic table.columns) on the periodic table.

all have the same number of valence (outer shell) electrons, which all have the same number of valence (outer shell) electrons, which governs their chemical behavior.governs their chemical behavior.

Atomic RadiusAtomic RadiusRadius is the distance from the center of Radius is the distance from the center of the nucleus to the the nucleus to the ““edgeedge”” of the electron of the electron cloud.cloud.

Since a cloudSince a cloud’’s edge is difficult to define, s edge is difficult to define, scientists use covalent radius, or half the scientists use covalent radius, or half the distance between the nuclei of 2 bonded atoms.distance between the nuclei of 2 bonded atoms.

Atomic radii are usually measured in Atomic radii are usually measured in picometers (pm) or angstroms (Å). An angstrom picometers (pm) or angstroms (Å). An angstrom is 1 x 10is 1 x 10-10-10 m. m.

Ex. Two Br atoms bonded together are 2.86 Ex. Two Br atoms bonded together are 2.86 angstroms angstroms

apart. So, the radius of each apart. So, the radius of each

atom is 1.43 Å.atom is 1.43 Å.2.86 Å

1.43 Å 1.43 Å

The trend for atomic radius The trend for atomic radius smaller at the top to larger at the bottom.smaller at the top to larger at the bottom.

add an entirely new energy level to the electron cloud, making the add an entirely new energy level to the electron cloud, making the atoms larger with each step.atoms larger with each step.

The trend across a horizontal period is less obvious.The trend across a horizontal period is less obvious.Each step from left to right adds a proton and an electron (and 1 or 2 Each step from left to right adds a proton and an electron (and 1 or 2 neutrons) and electrons are added to existing energy levels.neutrons) and electrons are added to existing energy levels.

The effect is that the more positive nucleus has a greater pull on the The effect is that the more positive nucleus has a greater pull on the electron cloud.electron cloud.

The nucleus is more positive and the electron cloud is more negative.The nucleus is more positive and the electron cloud is more negative.

The The increased attraction pulls the cloud inincreased attraction pulls the cloud in, making atoms smaller as we , making atoms smaller as we move from left to right across a period.move from left to right across a period.

Ionization EnergyIonization EnergyIf an electron is given enough energy to overcome the forces If an electron is given enough energy to overcome the forces holding it in the cloud, it can leave the atom completely.holding it in the cloud, it can leave the atom completely.

The atom has been The atom has been ““ionizedionized”” or charged. The number of protons or charged. The number of protons and electrons is no longer equal.and electrons is no longer equal.The energy required to remove an electron from an atom is The energy required to remove an electron from an atom is ionization energy. (measured in kilojoules, kJ)ionization energy. (measured in kilojoules, kJ)

The larger the atom is, the easier its electrons are to remove.The larger the atom is, the easier its electrons are to remove.Ionization energy and atomic radius are inversely proportional.Ionization energy and atomic radius are inversely proportional.

Electron AffinityElectron AffinityElectron affinity is the energy Electron affinity is the energy changechange that occurs when an atom that occurs when an atom gains an electrongains an electron (also measured in kJ). (how well atoms attract (also measured in kJ). (how well atoms attract electrons)electrons)

Electron affinity is usually exothermic, but Electron affinity is usually exothermic, but not alwaysnot always..

Electron affinity is exothermic if there is an empty Electron affinity is exothermic if there is an empty or partially empty orbital for an electron to or partially empty orbital for an electron to occupy.occupy.If there are no empty spaces, a new orbital or If there are no empty spaces, a new orbital or energy level must be created, making the process energy level must be created, making the process endothermic.endothermic.

Metals: Metals like to lose valence electrons to form cations to have Metals: Metals like to lose valence electrons to form cations to have a fully stable octet. They absorb energy to lose electrons. The a fully stable octet. They absorb energy to lose electrons. The electron affinity of metals is lower than that of nonmetals.electron affinity of metals is lower than that of nonmetals.Nonmetals: Nonmetals like to gain electrons to form anions to have Nonmetals: Nonmetals like to gain electrons to form anions to have a fully stable octet. They release energy to gain electrons to form an a fully stable octet. They release energy to gain electrons to form an anion; thus, electron affinity of nonmetals is higher than that of anion; thus, electron affinity of nonmetals is higher than that of metals.metals.

ElectronegativityElectronegativityElectronegativity is a measure of an atomElectronegativity is a measure of an atom’’s attraction for another s attraction for another atomatom’’s electrons.s electrons.

It is an arbitrary scale that ranges from 0 to 4.It is an arbitrary scale that ranges from 0 to 4.The units of electronegativity are Paulings.The units of electronegativity are Paulings.Generally, metals are electron givers and have low Generally, metals are electron givers and have low electronegativities.electronegativities.Nonmetals are are electron takers and have high Nonmetals are are electron takers and have high electronegativities. electronegativities. What about the noble gases?What about the noble gases?

Periodic Trends Rap

Electron ConfigurationElectron ConfigurationQuantum Mechanical Model (electron cloud)Quantum Mechanical Model (electron cloud)

Energy is quantized. It comes in chunks.Energy is quantized. It comes in chunks.

A quanta is the amount of energy needed to A quanta is the amount of energy needed to move from one energy level to another.move from one energy level to another.

Since the energy of an atom is never Since the energy of an atom is never ““in in betweenbetween”” there must be a quantum leap in there must be a quantum leap in energy.energy.

Schrödinger derived an equation that described Schrödinger derived an equation that described the energy and position of the electrons in an the energy and position of the electrons in an atomatom

Atomic OrbitalsAtomic OrbitalsWithin each energy level the Within each energy level the complex math of Schrödinger's complex math of Schrödinger's equation describes several equation describes several shapes.shapes.

These are called atomic orbitalsThese are called atomic orbitalsRegions where there is a high Regions where there is a high probability of finding an probability of finding an electronelectron

S orbitalsS orbitals

• 1 s orbital in1 s orbital in

every energy levelevery energy level

1s 2s1s 2s 3s 3s

• Spherical shapedSpherical shaped

• Each s orbital can hold 2 electronsEach s orbital can hold 2 electrons

• Called the 1s, 2s, 3s, etc.. orbitalsCalled the 1s, 2s, 3s, etc.. orbitals

P orbitalsP orbitals• Start at the second Start at the second

energy level energy level

• 3 different 3 different directionsdirections

• 3 different shapes3 different shapes

• Each orbital can hold Each orbital can hold 2 electrons2 electrons

• The p Sublevel has The p Sublevel has 3 p orbitals3 p orbitals

• Called the 2p, 3p, Called the 2p, 3p, etc.etc.

D orbitalsD orbitals• The D sublevel starts in the 3The D sublevel starts in the 3rdrd

energy level energy level

• 5 different shapes (orbitals)5 different shapes (orbitals)

• Each orbital can hold 2 electronsEach orbital can hold 2 electrons

• The D sublevel has 5 D orbitalsThe D sublevel has 5 D orbitals

• Called the 3d, 4d, etc.Called the 3d, 4d, etc.

F orbitalsF orbitals• The F sublevel starts in the fourth The F sublevel starts in the fourth

energy levelenergy level

• The F sublevel has seven different The F sublevel has seven different shapes (orbitals)shapes (orbitals)

• 2 electrons per orbital2 electrons per orbital

• The F sublevel has 7 F orbitalsThe F sublevel has 7 F orbitals

• ONLY 4F and 5FONLY 4F and 5F

SummarySummary

s

p

d

f

# of shapes (orbitals)

Max # of electrons

1 2 1

3 6 2

5 10 3

7 14 4

SublevelStarts at energy level

Atomic OrbitalsAtomic Orbitals

• The periodic table gives clues to how The periodic table gives clues to how electrons fill each energy level (shell)electrons fill each energy level (shell)

• Principal Quantum Number (n) = the Principal Quantum Number (n) = the energy level of the electron. (same as energy level of the electron. (same as the period it’s in)the period it’s in)

• Three ways to represent where Three ways to represent where electrons areelectrons are

• Electron ConfigurationElectron Configuration

• Noble Gas ConfigurationNoble Gas Configuration

• Orbital NotationOrbital Notation

Orbital Filling Orbital Filling Rules!!!!Rules!!!!

• Aufbau principleAufbau principle- electrons enter the - electrons enter the lowest energy first.lowest energy first.– This causes difficulties because of the This causes difficulties because of the

overlap of orbitals of different overlap of orbitals of different energies.energies.

• Pauli Exclusion PrinciplePauli Exclusion Principle- at most 2 - at most 2 electrons per orbital - different spinselectrons per orbital - different spins

• HundHund’’s Rules Rule- When electrons occupy - When electrons occupy orbitals of equal energy they donorbitals of equal energy they don’’t t pair up until they have to .pair up until they have to .

Stable Electron ConfigurationsStable Electron Configurations• All elements on the periodic table (except for Noble All elements on the periodic table (except for Noble

Gases) have incomplete outer energy levelsGases) have incomplete outer energy levels– Valence electronselectrons in outer energy level of atomValence electronselectrons in outer energy level of atom

• Elements will gain, lose, or share electrons to get full Elements will gain, lose, or share electrons to get full outer levels (octet rule)outer levels (octet rule)– Eight electrons = STABLE!!!Eight electrons = STABLE!!!

• Electron dot diagrams help to visualize valence Electron dot diagrams help to visualize valence electronselectrons– Symbol represents nucleus and inner electronsSymbol represents nucleus and inner electrons– Dots represent valence electronsDots represent valence electrons– Group # = valence electronsGroup # = valence electrons

IonsIons• Charged atoms where the number of protons and Charged atoms where the number of protons and

electrons is not equalelectrons is not equal

• Charge indicates how many electrons are added or Charge indicates how many electrons are added or subtractedsubtracted– Negative charge- ADD electronsNegative charge- ADD electrons– Positive charge- SUBTRACT electronsPositive charge- SUBTRACT electrons– Example Sodium ionExample Sodium ion

• Na Na atomic number 11 = 11 electrons atomic number 11 = 11 electrons• NaNa++ subtract one electron = 10 electrons subtract one electron = 10 electrons

Drawing Electron Dot Drawing Electron Dot DiagramsDiagrams

• Determine number of valence electrons from periodic tableDetermine number of valence electrons from periodic table

• Draw the symbol for the elementDraw the symbol for the element

• Place dots around the symbol, one per side, until all valence Place dots around the symbol, one per side, until all valence electrons are accounted forelectrons are accounted for

• Example- Aluminum with 3 valence electronsExample- Aluminum with 3 valence electrons

Al

A Chemical BondA Chemical Bond• Forces that hold groups of atoms together and make Forces that hold groups of atoms together and make

them function as a unit.them function as a unit.

• A bond will form if the energy of the pairing is lower A bond will form if the energy of the pairing is lower than that of the separate atoms.than that of the separate atoms.

• Some elements have stronger attractions to e- when Some elements have stronger attractions to e- when bonded- helps to predictbonded- helps to predict– ELECTRONEGATIVITY (EN)ELECTRONEGATIVITY (EN)

• Relative attraction an atom has for shared electrons in a Relative attraction an atom has for shared electrons in a covalent bondcovalent bond

• Unit- paulingsUnit- paulings• Arbitrary number used for comparison purposes Arbitrary number used for comparison purposes

– F is 4.0, Cs/Fr 0.7F is 4.0, Cs/Fr 0.7

Copyright © Cengage Learning. All rights reservedCopyright © Cengage Learning. All rights reserved 3636

Arrange the following bonds from Arrange the following bonds from most to least polarmost to least polar: :

a) a) N–FN–F O–FO–F C–FC–F

b)b) CC––FF NN––OO SiSi––FF

c)c) Cl–ClCl–Cl B–ClB–Cl S–ClS–Cl

a)a) C–F, C–F, N–F, N–F, O–FO–F

b)b) Si–F, Si–F, C–F, C–F, N–ON–O

c)c) B–Cl, B–Cl, S–Cl, S–Cl, Cl–Cl Cl–Cl

Types of Chemical BondsTypes of Chemical Bonds• Ionic BondsIonic Bonds

– Some elements achieve stable configurations by transferring Some elements achieve stable configurations by transferring electronselectrons• Example- sodium and chlorineExample- sodium and chlorine• Sodium 1 valence electron Chlorine 7 valence electronsSodium 1 valence electron Chlorine 7 valence electrons• Both want to be stableBoth want to be stable• Sodium will lose the one electron, and chlorine will gain that electron, Sodium will lose the one electron, and chlorine will gain that electron,

forming IONS (atoms that have gained or lost electrons)forming IONS (atoms that have gained or lost electrons)


Na+ Cl-

• Charge on ion represented by + or – signCharge on ion represented by + or – sign

• Positive ion- cationPositive ion- cation

• Negative ion- anion (use suffix –ide)Negative ion- anion (use suffix –ide)

• NaNa++ClCl- - is sodium chloride (NaCl) is sodium chloride (NaCl)

• Groups 1, 2, and 3 will lose electronsGroups 1, 2, and 3 will lose electrons

• Groups 5, 6, and 7 will gain electronsGroups 5, 6, and 7 will gain electrons

• Group 4 will go either wayGroup 4 will go either way

• Ionic compounds- compounds that contain ionic Ionic compounds- compounds that contain ionic bondsbonds

• Chemical formula- shows ratios of ions contained Chemical formula- shows ratios of ions contained in the bondin the bond– NaNa++ClCl- - one to one NaCl one to one NaCl– MgMg2+2+ClCl- - one to two MgCl one to two MgCl22

• Crystal LatticesCrystal Lattices– Each ionic compound makes specific shape based on Each ionic compound makes specific shape based on

arrangementarrangement– Crystal- solid whose particles are arranged in a lattice Crystal- solid whose particles are arranged in a lattice

structure (NaCl- cubes, ruby- hexagonal)structure (NaCl- cubes, ruby- hexagonal)

• Properties of ionic compoundsProperties of ionic compounds– High melting point, boiling pointHigh melting point, boiling point– Poor conductor when solid, good when molten/dissolvedPoor conductor when solid, good when molten/dissolved– Crystal structure- shatters when hitCrystal structure- shatters when hit

• Covalent BondsCovalent Bonds– Nonmetals have high ionization energyNonmetals have high ionization energy

• DonDon’’t usually form ions-share electrons to t usually form ions-share electrons to get to stable energy levelget to stable energy level

• Covalent bond-chemical bond in which two Covalent bond-chemical bond in which two atoms share a pair of valence electronsatoms share a pair of valence electrons– May share one (single bond), two (double May share one (single bond), two (double

bond), or three pairs (triple bond)bond), or three pairs (triple bond)

4343

Chemical BondsChemical Bonds– Form moleculesForm molecules

• Neutral group of atoms that are joined together by Neutral group of atoms that are joined together by one or more covalent bondsone or more covalent bonds

• May exist as diatomic moleculesMay exist as diatomic molecules– Made of 2 atoms of same elementMade of 2 atoms of same element

Chemical BondsChemical Bonds• May form single or multiple bondsMay form single or multiple bonds

• Subscript tells how many of each element are Subscript tells how many of each element are presentpresent

Chemical BondsChemical Bonds• When atoms share electrons, they rarely share equallyWhen atoms share electrons, they rarely share equally

• One element will One element will ““attractattract”” electrons more than the electrons more than the othersothers

• Polar Covalent Bond- a covalent bond in which Polar Covalent Bond- a covalent bond in which electrons are not shared equallyelectrons are not shared equally– Atom with greater attraction gets a partial negative charge Atom with greater attraction gets a partial negative charge

((δδ-), lesser attraction partial positive charge (-), lesser attraction partial positive charge (δδ+)+)

http://www.uoregon.edu/~ch111/images/hfpolar.gif

Naming CompoundsNaming Compounds• Binary CompoundsBinary Compounds

– Composed of two elementsComposed of two elements– Ionic and covalent compounds includedIonic and covalent compounds included

• Binary Ionic CompoundsBinary Ionic Compounds– Metal—nonmetalMetal—nonmetal

• Binary Covalent CompoundsBinary Covalent Compounds– Nonmetal—nonmetalNonmetal—nonmetal


Stereochemistry- VSEPR TheoryStereochemistry- VSEPR Theory

• All molecules have 3D shapeAll molecules have 3D shape

• Stereochemistry- study of shapes of moleculesStereochemistry- study of shapes of molecules

• VSEPR theoryVSEPR theory– VValence alence SShell hell EElectron lectron PPair air RRepulsionepulsion

– Helps to understand and predict molecuar geometry Helps to understand and predict molecuar geometry (from Lewis Dot diagrams)(from Lewis Dot diagrams)

– Developed by Gillespie and Nyholm in 1956-57Developed by Gillespie and Nyholm in 1956-57

– Rules based on the idea that the arrangement in Rules based on the idea that the arrangement in space of the covalent bonds formed by an atom space of the covalent bonds formed by an atom depends on the arrangement of valence e-depends on the arrangement of valence e-• e- try to push each other far away while still bonding to e- try to push each other far away while still bonding to

central atomcentral atom

• Restricted VSEPR rulesRestricted VSEPR rules– Valence e- pairs (both shared and lone) arrange Valence e- pairs (both shared and lone) arrange

themselves around the central atom in a molecule themselves around the central atom in a molecule in such a way as to minimize repulsion (as far in such a way as to minimize repulsion (as far away from each other as possible)away from each other as possible)

– When predicting molecular geometry, double and When predicting molecular geometry, double and triple bonds act like single bondstriple bonds act like single bonds

– Lone pairs of e- occupy more space than bonding Lone pairs of e- occupy more space than bonding e-e-

• Steps to draw VSEPR moleculesSteps to draw VSEPR molecules– Draw Lewis DiagramDraw Lewis Diagram

– Count the number of bonding and lone pairs Count the number of bonding and lone pairs surrounding the central atomsurrounding the central atom• Multiple bonds count as one pairMultiple bonds count as one pair

– Shape molecule in order to minimize repulsionShape molecule in order to minimize repulsion

Stereochemistry- VSEPR TheoryStereochemistry- VSEPR Theory• All molecules have 3D shapeAll molecules have 3D shape

• Stereochemistry- study of shapes of moleculesStereochemistry- study of shapes of molecules

• VSEPR theoryVSEPR theory– VValence alence SShell hell EElectron lectron PPair air RRepulsionepulsion– Helps to understand and predict molecuar geometry Helps to understand and predict molecuar geometry

(from Lewis Dot diagrams)(from Lewis Dot diagrams)– Developed by Gillespie and Nyholm in 1956-57Developed by Gillespie and Nyholm in 1956-57– Rules based on the idea that the arrangement in Rules based on the idea that the arrangement in

space of the covalent bonds formed by an atom space of the covalent bonds formed by an atom depends on the arrangement of valence e-depends on the arrangement of valence e-• e- try to push each other far away while still bonding to e- try to push each other far away while still bonding to

central atomcentral atom• e- pair repulsione- pair repulsion

• Restricted VSEPR rulesRestricted VSEPR rules– Valence e- pairs (both shared and lone) arrange Valence e- pairs (both shared and lone) arrange

themselves around the central atom in a molecule themselves around the central atom in a molecule in such a way as to minimize repulsion (as far in such a way as to minimize repulsion (as far away from each other as possible)away from each other as possible)

– When predicting molecular geometry, double and When predicting molecular geometry, double and triple bonds act like single bondstriple bonds act like single bonds

– Lone pairs of e- occupy more space than bonding Lone pairs of e- occupy more space than bonding e-e-

• Steps to draw VSEPR moleculesSteps to draw VSEPR molecules– Draw Lewis DiagramDraw Lewis Diagram

– Determine the central atom (lowest EN)Determine the central atom (lowest EN)

– Count the number of bonding and lone pairs Count the number of bonding and lone pairs surrounding the central atomsurrounding the central atom• Multiple bonds count as one pairMultiple bonds count as one pair

– Shape molecule in order to minimize repulsionShape molecule in order to minimize repulsion• Find on VSEPR chartFind on VSEPR chart

EXAMPLESEXAMPLES

• Water, HWater, H22OO

– 2 bond pairs2 bond pairs

– 2 lone pairs2 lone pairs– The molecular The molecular

geometry geometry is is BENTBENT..

H O H••

••

H O H••

••

http://en.wikibooks.org/wiki/Image:Carbon-dioxide-3D-balls.png

unit 3 periodic trends, electron configurations, and bonding

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