Periodic TrendsPeriodic Trends

Mrs.KayMrs.Kay

Groups: vertical columns (18)Groups: vertical columns (18)Have similar properties because have Have similar properties because have

same number of electrons in outer shellsame number of electrons in outer shellPeriods: horizontal columns (7)Periods: horizontal columns (7)

Valence electrons: Valence electrons: electrons found in electrons found in the outer most the outer most shell or valence shell or valence shellshell

Each energy Each energy level/shell holds on level/shell holds on a certain number a certain number of electronsof electrons

Alkali metals all end in sAlkali metals all end in s11

Alkaline earth metals all end in Alkaline earth metals all end in ss22

really have to include He but it really have to include He but it fits better later.fits better later.

He has the properties of the He has the properties of the noble gases.noble gases.

s2s1 S- blockS- block

Transition Metals -d blockTransition Metals -d block

d1 d2 d3s1

d5 d5 d6 d7 d8s1

d10 d10

The P-The P-blockblock p1 p2 p3 p4 p5 p6

F - blockF - block inner transition elementsinner transition elements

f1 f5f2 f3 f4

f6 f7 f8 f9 f10 f11 f12 f14

f13

Metals: Metals: To the left of the staircase line To the left of the staircase line

Physical Physical PropertiesProperties:: Luster (shiny)Luster (shiny) Good Good

conductorsconductors High densityHigh density High melting High melting

pointpoint MalleableMalleable

Chemical Chemical Properties:Properties:

Easily lose Easily lose electronselectrons

Corrode easily Corrode easily (ex: rusting or (ex: rusting or tarnishing)tarnishing)

Low Low electronegativityelectronegativity

Non metals: Non metals: to the right of the staircase to the right of the staircase lineline

Physical Properties:Physical Properties: DullDull Poor conductorPoor conductor BrittleBrittle Not malleableNot malleable Low density and Low density and

melting pointmelting point

• Chemical Property:Chemical Property: Tend to gain Tend to gain

electronselectrons High electronegativityHigh electronegativity

Metalloids: Metalloids: along the staircase linealong the staircase line

SolidsSolids Shiny or dullShiny or dull MalleableMalleable Conduct heat and Conduct heat and

electricity better electricity better than non metal but than non metal but not as well as not as well as metalsmetals

Atomic SizeAtomic Size

Atomic SizeAtomic SizeThe electron cloud doesn’t have a The electron cloud doesn’t have a

definite edge.definite edge.They get around this by measuring They get around this by measuring

more than 1 atom at a time.more than 1 atom at a time.Summary: it is the volume that an Summary: it is the volume that an

atom takes upatom takes up

Atomic SizeAtomic Size

Atomic Radius = half the distance between Atomic Radius = half the distance between two nuclei of a diatomic molecule.two nuclei of a diatomic molecule.

}Radius

Group trendsGroup trendsAs we go down a As we go down a

group (each atom group (each atom has another has another energy level) the energy level) the atoms get bigger, atoms get bigger, because more because more protons and protons and neutrons in the neutrons in the nucleusnucleus

HLi

Na

K

Rb

Periodic TrendsPeriodic Trendsatomic radius decreases as you go from left to atomic radius decreases as you go from left to

right across a period. right across a period. WhyWhy? Stronger attractive forces in atoms (as ? Stronger attractive forces in atoms (as

you go from left to right) between the opposite you go from left to right) between the opposite charges in the nucleus and electron cloud charges in the nucleus and electron cloud cause the atom to be 'sucked' together a little cause the atom to be 'sucked' together a little tighter.tighter.

Na Mg Al Si P S Cl Ar

ReactivityReactivity

ReactivityReactivity

Reactivity refers to how likely or Reactivity refers to how likely or vigorously an atom is to react with vigorously an atom is to react with other substances. This is usually other substances. This is usually determined by how easily electrons determined by how easily electrons can be removed (ionization energy) can be removed (ionization energy) and how badly they want to take and how badly they want to take other atom's electrons other atom's electrons

For Metals:For Metals:

PeriodPeriod - reactivity decreases as you - reactivity decreases as you go from left to right across a period. go from left to right across a period. GroupGroup - reactivity increases as you - reactivity increases as you go down a group go down a group

Why? The farther to the left and Why? The farther to the left and down the periodic chart you go, the down the periodic chart you go, the easier it is for electrons to be given easier it is for electrons to be given or taken away, resulting in higher or taken away, resulting in higher reactivity reactivity

For Non-metalsFor Non-metals

PeriodPeriod - reactivity increases as you - reactivity increases as you go from the left to the right across a go from the left to the right across a period. period. GroupGroup - reactivity decreases as you - reactivity decreases as you go down the group. go down the group.

Why? The farther right and up you go Why? The farther right and up you go on the periodic table, the higher the on the periodic table, the higher the electronegativity, resulting in a more electronegativity, resulting in a more vigorous exchange of electron.vigorous exchange of electron.

Ionization EnergyIonization Energy

Ionization EnergyIonization EnergyThe amount of energy required to The amount of energy required to

completely remove an electron from a completely remove an electron from a gaseous atom.gaseous atom.

An atom's 'desire' to grab another An atom's 'desire' to grab another atom's electrons. atom's electrons.

Removing one electron makes a +1 ion.Removing one electron makes a +1 ion.The energy required is called the first The energy required is called the first

ionization energy.ionization energy.

XX(g) (g) + energy+ energy →X →X++ + e- + e-

Ionization EnergyIonization Energy

The second and third ionization The second and third ionization energies can be represented as energies can be represented as follows:follows:

  XX++ (g)(g) + energy + energy X X2+ 2+ (g)(g) + e- + e-

XX2+2+ (g)(g) + energy + energy X X3+ 3+ (g)(g) + e- + e-

More energy required to remove 2More energy required to remove 2ndnd electron, and still more energy electron, and still more energy required to remove 3required to remove 3rdrd electron electron

Group trendsGroup trends Ionization energy decreases down the Ionization energy decreases down the

group.group.

Going from Mg to Be, IE decreases because:Going from Mg to Be, IE decreases because: Be outer electron is in the 3s sub-shell rather Be outer electron is in the 3s sub-shell rather

than the 2s. This is higher in energythan the 2s. This is higher in energy The 3s electron is further from the nucleus and The 3s electron is further from the nucleus and

shielded by the inner electronsshielded by the inner electrons So the 3s electron is more easily removedSo the 3s electron is more easily removed

A similar decrease occurs in every group A similar decrease occurs in every group in the periodic table.in the periodic table.

Period trendsPeriod trendsIE generally increases from left to right.IE generally increases from left to right.Why?Why?    From Na to Ar (11 protons to 18 From Na to Ar (11 protons to 18

protons), the nuclear charge in each protons), the nuclear charge in each element increases.element increases.

   The electrons are attracted more The electrons are attracted more strongly to the nucleus – so it takes strongly to the nucleus – so it takes more energy to remove one from the more energy to remove one from the atom.atom.

Why is there a fall from Mg to Why is there a fall from Mg to Al?Al?

  Al has configuration 1s2 2s2 2p6 3s2 Al has configuration 1s2 2s2 2p6 3s2 3p1, its outer electron is in a p 3p1, its outer electron is in a p sublevelsublevel

   Mg has electronic configuration 1s2 Mg has electronic configuration 1s2 2s2 2p6 3s2.2s2 2p6 3s2.

   The p level is higher in energy and The p level is higher in energy and with Mg the s sub level is full – with Mg the s sub level is full – this this gives it a slight stability advantagegives it a slight stability advantage

Why is there a fall from P to Why is there a fall from P to S?S?

   This can be explained in terms of electron This can be explained in terms of electron pairing.pairing.

   As the p sublevel fills up, electrons fill up As the p sublevel fills up, electrons fill up the vacant sub levels and are unpaired.the vacant sub levels and are unpaired.

This configuration is more energetically This configuration is more energetically stable than S as stable than S as all the electrons are all the electrons are unpaired.unpaired. It requires more energy to pair up It requires more energy to pair up the electrons in S so it has a lower Ionisation the electrons in S so it has a lower Ionisation energy.energy.

There is some repulsion between the paired There is some repulsion between the paired electrons which lessens their attraction to electrons which lessens their attraction to the nucleus.the nucleus.

   It becomes easier to remove!It becomes easier to remove!

Driving ForceDriving ForceFull Energy Levels are very low Full Energy Levels are very low

energy.energy.Noble Gases have full energy levels.Noble Gases have full energy levels.Atoms behave in ways to achieve Atoms behave in ways to achieve

noble gas configuration.noble gas configuration.

22ndnd Ionization Energy Ionization EnergyFor elements that reach a filled or For elements that reach a filled or

half filled sublevel by removing 2 half filled sublevel by removing 2 electrons 2electrons 2ndnd IE is lower than IE is lower than expected.expected.

Makes it easier to achieve a full outer Makes it easier to achieve a full outer shellshell

True for sTrue for s2 2

Alkaline earth metals form +2 ions.Alkaline earth metals form +2 ions.

33rdrd IE IEUsing the same logic sUsing the same logic s22pp11

atoms have atoms have an low 3an low 3rdrd IE. IE.

Atoms in the aluminum family form Atoms in the aluminum family form +3 ions.+3 ions.

22ndnd IE and 3 IE and 3rdrd IE are always higher IE are always higher than 1than 1stst IE!!! IE!!!

Electron AffinityElectron Affinity

Electron AffinityElectron AffinityThe energy change associated with The energy change associated with

adding an electron to a gaseous atom.adding an electron to a gaseous atom.Easiest to add to group 7A.Easiest to add to group 7A.Gets them to full energy level.Gets them to full energy level. Increase from left to right atoms Increase from left to right atoms

become smaller, with greater nuclear become smaller, with greater nuclear charge.charge.

Decrease as we go down a group.Decrease as we go down a group.

Ionization energy, electronegativity

Electron affinity INCREASE

Atomic size increases, shielding constant

Ionic size increases

Ionic SizeIonic SizeCations form by losing electrons.Cations form by losing electrons.Cations are smaller than the atom Cations are smaller than the atom

they come from.they come from.Metals form cations.Metals form cations.Cations of representative elements Cations of representative elements

have noble gas configuration.have noble gas configuration.

Ionic sizeIonic sizeAnions form by gaining electrons.Anions form by gaining electrons.Anions are bigger than the atom they Anions are bigger than the atom they

come from.come from.Nonmetals form anions.Nonmetals form anions.Anions of representative elements Anions of representative elements

have noble gas configuration.have noble gas configuration.

Configuration of IonsConfiguration of Ions Ions always have noble gas Ions always have noble gas

configuration.configuration.Na is 1sNa is 1s222s2s222p2p663s3s11 Forms a +1 ion : 1sForms a +1 ion : 1s222s2s222p2p66 Same configuration as neon.Same configuration as neon.Metals form ions with the Metals form ions with the

configuration of the noble gas before configuration of the noble gas before them - they lose electrons.them - they lose electrons.

Configuration of IonsConfiguration of IonsNon-metals form ions by gaining Non-metals form ions by gaining

electrons to achieve noble gas electrons to achieve noble gas configuration.configuration.

They end up with the configuration of They end up with the configuration of the noble gas after them.the noble gas after them.

Periodic TrendsPeriodic TrendsAcross the period nuclear charge Across the period nuclear charge

increases so they get smaller.increases so they get smaller.Energy level changes between Energy level changes between

anions and cations.anions and cations.

Li+1

Be+2

B+3

C+4

N-3O-2 F-1

Size of Isoelectronic ionsSize of Isoelectronic ions Iso - sameIso - same Iso electronic ions have the same # Iso electronic ions have the same #

of electronsof electronsAlAl+3+3 Mg Mg+2 +2 NaNa+1 +1 Ne FNe F-1 -1 OO-2 -2 and Nand N-3-3 all have 10 electronsall have 10 electronsall have the configuration 1sall have the configuration 1s222s2s222p2p66

Size of Isoelectronic ionsSize of Isoelectronic ionsPositive ions have more protons so Positive ions have more protons so

they are smaller.they are smaller.

Al+3

Mg+2

Na+1 Ne F-1 O-2 N-3

ElectronegativityElectronegativity

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ElectronegativityElectronegativityThe tendency for an atom to attract The tendency for an atom to attract

electrons to itself when it is chemically electrons to itself when it is chemically combined with another element.combined with another element.

How fair it shares.How fair it shares.Big electronegativity means it pulls Big electronegativity means it pulls

the electron toward it.the electron toward it.Atoms with large negative electron Atoms with large negative electron

affinity have larger electronegativity.affinity have larger electronegativity.

Group TrendGroup Trend The further down a The further down a groupgroup the farther the the farther the

electron is away and the more electrons an electron is away and the more electrons an atom has.atom has.

So as you go from fluorine to chlorine to So as you go from fluorine to chlorine to bromine and so on down the periodic table, bromine and so on down the periodic table, the the electrons are further away from the electrons are further away from the nucleusnucleus and better shielded from the and better shielded from the nuclear charge and thus not as attracted to nuclear charge and thus not as attracted to the nucleus. For that reason the the nucleus. For that reason the electronegativity decreaseselectronegativity decreases as you go as you go down the periodic table. down the periodic table.

Period TrendPeriod Trend

Electronegativity increases from left Electronegativity increases from left to right across a to right across a periodperiod

When the When the nuclear charge nuclear charge increasesincreases, so will the attraction that , so will the attraction that the atom has for electrons in its the atom has for electrons in its outermost energy level and that outermost energy level and that means the means the electronegativity will electronegativity will increaseincrease

Period trendPeriod trendElectronegativity increases as you go from left Electronegativity increases as you go from left

to right across a period. to right across a period. WhyWhy? Elements on the left of the period ? Elements on the left of the period

table have 1 -2 valence electrons and would table have 1 -2 valence electrons and would rather give those few valence electrons away rather give those few valence electrons away (to achieve the octet in a lower energy level) (to achieve the octet in a lower energy level) than grab another atom's electrons. As a than grab another atom's electrons. As a result, they have low electronegativity. result, they have low electronegativity. Elements on the right side of the period table Elements on the right side of the period table only need a few electrons to complete the only need a few electrons to complete the octet, so they have strong desire to grab octet, so they have strong desire to grab another atom's electrons.another atom's electrons.

Group TrendGroup Trend

electronegativity decreases as you go down a group. electronegativity decreases as you go down a group. WhyWhy? Elements near the top of the period table ? Elements near the top of the period table

have few electrons to begin with; every electron is have few electrons to begin with; every electron is a big deal. They have a stronger desire to acquire a big deal. They have a stronger desire to acquire more electrons. Elements near the bottom of the more electrons. Elements near the bottom of the chart have so many electrons that loosing or chart have so many electrons that loosing or acquiring an electron is not as big a deal. acquiring an electron is not as big a deal.

This is due to the shielding affect where electrons This is due to the shielding affect where electrons in lower energy levels shield the positive charge of in lower energy levels shield the positive charge of the nucleus from outer electrons resulting in those the nucleus from outer electrons resulting in those outer electrons not being as tightly bound to the outer electrons not being as tightly bound to the atom.atom.

ShieldingShielding

Shielded slightly from Shielded slightly from the pull of the nucleus the pull of the nucleus by the electrons that by the electrons that are in the closer are in the closer orbitals.orbitals.

Look at this Look at this analogy analogy to help understand to help understand