Unit 5: PeriodicityUnit 5: Periodicity

History of the Periodic TableHistory of the Periodic Table

Dimitri MendeleevDimitri Mendeleev (1836-1907) (1836-1907)– Russian chemistry professorRussian chemistry professor

Noticed that as he was arranging Noticed that as he was arranging elements according to their elements according to their properties that they generally were properties that they generally were organized in order of increasing organized in order of increasing atomic massatomic mass..

Genius of Mendeleev’s WorkGenius of Mendeleev’s Work Left spaces for elements not yet discovered.Left spaces for elements not yet discovered. He predicted that some still-unknown elements He predicted that some still-unknown elements

must exist to fit in the holes.must exist to fit in the holes.

Mendeleev’s Periodic TableMendeleev’s Periodic Table

Contained 1 inconsistency.Contained 1 inconsistency.– He placed the elements in order of He placed the elements in order of atomic massatomic mass

Forced to break pattern a couple times to Forced to break pattern a couple times to preserve the patterns he had discovered.preserve the patterns he had discovered.

Henry MoseleyHenry Moseley• Once the proton was discovered Once the proton was discovered

by Rutherford, Moseley worked by Rutherford, Moseley worked with X-rays to determine how with X-rays to determine how many protons elements had.many protons elements had.

• He arranged the elements in order He arranged the elements in order of increasing of increasing atomic number.atomic number.

• The eliminated the inconsistencies The eliminated the inconsistencies seen in Mendeleev’s table. seen in Mendeleev’s table.

• He was killed at the age of 28 in He was killed at the age of 28 in WWI.WWI.

Periodic LawPeriodic Law

Periodic LawPeriodic Law: The properties of the : The properties of the elements are periodic functions of their elements are periodic functions of their atomic numbersatomic numbers. .

What this means is that if we arrange the What this means is that if we arrange the elements in elements in order of increasing atomic order of increasing atomic numbernumber, we will periodically encounter , we will periodically encounter elements that have similar chemical and elements that have similar chemical and physical properties. physical properties.

These elements appear in the same vertical These elements appear in the same vertical column (group).column (group).

ElementsElements

Science has come along Science has come along way since Aristotle’s way since Aristotle’s theory of Air, Water, theory of Air, Water, Fire, and Earth.Fire, and Earth.

Scientists have Scientists have identified 92 naturally identified 92 naturally occurring elements, and occurring elements, and created about 28 others.created about 28 others.

Periodic TablePeriodic Table We can learn a lot about an element We can learn a lot about an element

based on where it is based on where it is locatedlocated..

You can predict the You can predict the physical and physical and chemical propertieschemical properties and how an and how an element will element will reactreact..

Metals

NonmetalsMetalloids

LABEL THESE ON YOUR PERIODIC TABLE

Properties of MetalsProperties of Metals Good Good conductorsconductors of heat of heat

and electricity.and electricity. ShinyShiny DuctileDuctile (can be stretched (can be stretched

into thin wires).into thin wires). MalleableMalleable (can be (can be

pounded into thin pounded into thin sheets).sheets).

Reacts with water which Reacts with water which results in results in corrosioncorrosion..

Properties of Non-MetalsProperties of Non-Metals poor conductorspoor conductors of of

heat and electricity.heat and electricity. not ductile or not ductile or

malleable.malleable. Solid non-metals are Solid non-metals are

brittle and break brittle and break easily.easily.

dulldull Many non-metals are Many non-metals are

gasesgases..

Sulfur

Bromine

Properties of MetalloidsProperties of Metalloids MetalloidsMetalloids (metal-like) (metal-like)

have have properties of both properties of both metals and non-metals.metals and non-metals.

They are They are solidssolids that can that can be be shiny or dull.shiny or dull.

They They conduct heat and conduct heat and electricityelectricity better than non- better than non-metals but not as well as metals but not as well as metals.metals.

They are They are ductile and ductile and malleable.malleable.

Columns of elements are called Columns of elements are called groups or familiesgroups or families. .

Elements in each family have Elements in each family have similarsimilar but not identical but not identical propertiesproperties..

For example, lithium (Li), sodium For example, lithium (Li), sodium (Na), potassium (K), and other (Na), potassium (K), and other members of family 1 are all soft, members of family 1 are all soft, white, shiny metals.white, shiny metals.

All elements in a family have the All elements in a family have the same number of same number of valence electronsvalence electrons..

Each Each horizontal rowhorizontal row of elements is called a of elements is called a periodperiod.. The elements in a The elements in a periodperiod are not alikeare not alike in properties. in properties. In fact, the properties change greatly across even given In fact, the properties change greatly across even given

row.row. The The first elementfirst element in a period is always an extremely in a period is always an extremely

active solidactive solid. The last element in a period, is . The last element in a period, is alwaysalways an an inactive gasinactive gas..

HydrogenHydrogen The hydrogen square sits atop Family 1, but The hydrogen square sits atop Family 1, but

it is not a member of that family. it is not a member of that family. Hydrogen is Hydrogen is in a class of its own.in a class of its own.

It’s a gas at room temperature.It’s a gas at room temperature. It has one proton and one electron in its one It has one proton and one electron in its one

and only energy level.and only energy level. Hydrogen Hydrogen only needs 2 electrons to fill up its only needs 2 electrons to fill up its

valence shell.valence shell.

Alkali MetalsAlkali Metals first columnfirst column of the of the

periodic tableperiodic table

1 valence electron1 valence electron

They are They are shinyshiny, have the , have the consistency of clayconsistency of clay, and , and are easily are easily cut with a cut with a knifeknife

That is Sodium!

Alkali MetalsAlkali Metals

most reactive metalsmost reactive metals react violently with react violently with

waterwater never found as free never found as free

elements in nature. elements in nature. They are They are always always bonded with another bonded with another element.element.

That is sodium on top of the water.

Alkaline Earth MetalsAlkaline Earth Metals

never found alonenever found alone in nature, always bonded with in nature, always bonded with something else.something else.

two valence electronstwo valence electrons

Transition MetalsTransition Metals

elements in the elements in the d-block d-block (Groups 3-12)(Groups 3-12)

These are the metals you These are the metals you are probably most familiarare probably most familiar

Transition ElementsTransition Elements

Transition elementsTransition elements have properties similar have properties similar to one another and to other metals, but their to one another and to other metals, but their properties do not fit in with those of any properties do not fit in with those of any other family. other family.

Many transition metals combine chemically Many transition metals combine chemically with oxygen to form compounds called with oxygen to form compounds called oxidesoxides. .

Boron FamilyBoron Family

The Boron Family is named The Boron Family is named after the first element in the after the first element in the family.family.

3 valence electrons3 valence electrons This family includes a This family includes a

metalloid (boron), and the metalloid (boron), and the rest are metals.rest are metals.

This family includes the This family includes the most abundant metal in the most abundant metal in the earth’s crust (aluminum).earth’s crust (aluminum).

Carbon FamilyCarbon Family

4 valence electrons4 valence electrons This family includes a non-This family includes a non-

metal (carbon), metalloids, metal (carbon), metalloids, and metals.and metals.

The element carbon is called The element carbon is called the “basis of life.” There is an the “basis of life.” There is an entire branch of chemistry entire branch of chemistry devoted to carbon devoted to carbon compounds called organic compounds called organic chemistry.chemistry.

Nitrogen FamilyNitrogen Family The nitrogen family is named The nitrogen family is named

after the element that makes after the element that makes up 78% of our atmosphere.up 78% of our atmosphere.

This family includes non-This family includes non-metals, metalloids, and metals, metalloids, and metals.metals.

5 valence electrons5 valence electrons. They . They tend to tend to shareshare electrons when electrons when they bondthey bond

Other elements in this family Other elements in this family are phosphorus, arsenic, are phosphorus, arsenic, antimony, and bismuth.antimony, and bismuth.

Oxygen FamilyOxygen Family 6 valence electrons6 valence electrons Most elements in this Most elements in this

family family share share electrons electrons when forming compounds.when forming compounds.

Oxygen is the most Oxygen is the most abundant element in the abundant element in the earth’s crust. It is earth’s crust. It is extremely active and extremely active and combines with almost all combines with almost all elements.elements.

Halogen FamilyHalogen Family 7 valence electrons7 valence electrons, ,

which explains why which explains why they are the most they are the most active non-metals. active non-metals. They are never found They are never found free in nature.free in nature.

Halogen atoms only Halogen atoms only need to need to gain 1 gain 1 electronelectron to fill their to fill their outermost energy outermost energy level.level.

They react with alkali They react with alkali metals to form salts.metals to form salts.

Noble GasesNoble Gases Noble Gases are colorless Noble Gases are colorless

gases that are extremely un-gases that are extremely un-reactive. reactive.

One important property of One important property of the noble gases is their the noble gases is their inactivity. They are inactive inactivity. They are inactive because their because their outermost outermost energy level is full. energy level is full.

Because they do not readily Because they do not readily combine with other combine with other elements to form elements to form compounds, the noble compounds, the noble gases are called gases are called inertinert..

All the noble gases are All the noble gases are found in small amounts in found in small amounts in the earth's atmosphere.the earth's atmosphere.

Rare Earth ElementsRare Earth Elements

The thirty rare earth The thirty rare earth elements are composed elements are composed of the lanthanide and of the lanthanide and actinide series.actinide series.

One element of the One element of the lanthanide series and lanthanide series and most of the elements in most of the elements in the actinide series are the actinide series are called trans-uranium, called trans-uranium, which means synthetic which means synthetic or man-made.or man-made.

Octet RuleOctet Rule

Octet means to have 8 valence electrons. Is associated with the stability of the noble gases. Helium (He) is stable with 2 valence electrons

Valence Electrons– He 1s2 2– Ne 1s2 2s2 2p6 8– Ar 1s2 2s2 2p6 3s2 3p6 8– Kr 1s2 2s2 2p63s2 3p6 4s2 3d10 4p6 8

Electron ShieldingElectron ShieldingShielding electrons are those electrons in the energy levels between the nucleus and the valence electrons.

They are called "shielding" electrons because they "shield" the valence electrons from being pulled closer to the nucleus.

Remember, the nucleus has a positive charge!

Periodic TrendsPeriodic Trends Trends in properties of the elements that follow a Trends in properties of the elements that follow a

pattern down a group and across a period in the pattern down a group and across a period in the periodic table. periodic table.

down a groupdown a group across a periodacross a period

Trends in Atomic Radius (size)Trends in Atomic Radius (size)

atomic radiusatomic radius: distance from distance from center of nucleus to edge of center of nucleus to edge of electron cloudelectron cloud

Atomic RadiusAtomic Radius group trendgroup trend:: increasesincreases going down a group. going down a group.

– As you move down a group, you As you move down a group, you add energy levelsadd energy levels, , thus thus increasing the sizeincreasing the size of the electron cloud, so the of the electron cloud, so the atoms get atoms get largerlarger..

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Atomic RadiusAtomic Radius periodic trendperiodic trend:: decreasesdecreases going going left to rightleft to right across a across a

period.period. Why?: You Why?: You are notare not adding energy levels, you are adding energy levels, you are

adding adding protonsprotons. As you do this, the nucleus gets a . As you do this, the nucleus gets a greater positive charge which pulls the electrons closer greater positive charge which pulls the electrons closer to it, decreasing the radius.to it, decreasing the radius.

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Atomic RadiusAtomic Radius

– Increases to the LEFT and DOWNIncreases to the LEFT and DOWN

Atomic RadiusAtomic Radius

Ionization EnergyIonization Energy

ionization energyionization energy:: the energy required to the energy required to remove a valence electron. remove a valence electron.

Trends in Ionization EnergyTrends in Ionization Energygroup trendgroup trend:: decreasesdecreases going down a group going down a group

This is due to the This is due to the shielding effectshielding effect - an electron in the - an electron in the outer energy level of a large atom is easier to remove outer energy level of a large atom is easier to remove because it is well-shielded from the pull of the nucleus because it is well-shielded from the pull of the nucleus by the inner electrons.by the inner electrons.

periodic trendperiodic trend:: increasesincreases going across a period going across a periodThis is due to This is due to nuclear chargenuclear charge - across a period, nuclear - across a period, nuclear charge increases, so they hold onto their electrons charge increases, so they hold onto their electrons tighter.tighter.

metalsmetals have a much greater tendency to have a much greater tendency to lose lose electronselectrons than nonmetals do. than nonmetals do.

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Ionization EnergyIonization Energy– Increases UP and to the RIGHTIncreases UP and to the RIGHT

Ionization EnergyIonization Energy

Trends in Electron AffinityTrends in Electron Affinity electron affinity (electron-liking): the energy change that the energy change that

accompanies the accompanies the additionaddition of an electron of an electron to an atom. to an atom. group trendgroup trend:: EA EA decreases going down a group.decreases going down a group.

– Why? It is harder to add an electron when it is so far away from the Why? It is harder to add an electron when it is so far away from the nucleus. The nucleus cannot “grab onto it”.nucleus. The nucleus cannot “grab onto it”.

periodic trendperiodic trend:: EA EA increasesincreases going across a period. going across a period.– Why? As the nuclear charge becomes more positive, it is able to Why? As the nuclear charge becomes more positive, it is able to

hold onto electrons better.hold onto electrons better.

– Note that this periodic trend supports the idea that Note that this periodic trend supports the idea that nonmetalsnonmetals have a much greater tendency to have a much greater tendency to gaingain electrons than metals doelectrons than metals do..

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Electron AffinityElectron Affinity– Increases UP and to the RIGHTIncreases UP and to the RIGHT

Electron AffinityElectron Affinity

Trends in ElectronegativityTrends in Electronegativity electronegativity: the tendency of an the tendency of an

atom to atom to attract electronsattract electrons to itself when it is to itself when it is chemically bondedchemically bonded with another element. with another element.

Diagram of water molecule:Diagram of water molecule:– In HIn H22O, oxygen is more electronegative than hydrogen, O, oxygen is more electronegative than hydrogen,

so it pulls the electrons closer, and thus obtains a so it pulls the electrons closer, and thus obtains a partially negative charge. partially negative charge.

Trends in ElectronegativityTrends in Electronegativity

group trendgroup trend:: decreasesdecreases down a group. down a group.Larger atoms have more energy levels, so it is Larger atoms have more energy levels, so it is harder for them to attract electrons to the nucleus harder for them to attract electrons to the nucleus (shielding effect).(shielding effect).

periodic trendperiodic trend:: increasesincreases across a period. across a period. The nuclear charge is greater with more protons and The nuclear charge is greater with more protons and can hold onto electrons closer to the nucleus.can hold onto electrons closer to the nucleus.

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ElectronegativityElectronegativity– Increases UP and to the RIGHTIncreases UP and to the RIGHT

ElectronegativityElectronegativity

Ionic RadiusIonic Radius

Ion: charged atomIon: charged atom When atoms When atoms loselose electrons, they become electrons, they become

positivepositive ions ions – More p+ than e-More p+ than e-

When atoms When atoms gaingain electrons, they become electrons, they become negativenegative ions. ions.

--more e- than p+more e- than p+

Positive IonsPositive Ions Example…Example… Sodium has 11 pSodium has 11 p++ and 11 e and 11 e--. To become the . To become the

sodium ion it loses an esodium ion it loses an e--. Now it has 11 p. Now it has 11 p++ and 10 eand 10 e--

Sodium Sodium atom Naatom Na Sodium Sodium ion Naion Na+1+1

Negative IonsNegative Ions

Example…Example… The oxygen atom has 8 p+ and 8 e-. The The oxygen atom has 8 p+ and 8 e-. The

oxygen ion gains 2 e-oxygen ion gains 2 e- to have a total of 8 p+ to have a total of 8 p+ and 10e-.and 10e-.

Ionic RadiusIonic Radius

Positive ionsPositive ions are are smaller smaller than the neutral than the neutral atom.atom.

This is because you remove valence This is because you remove valence electrons and they no longer have the outer electrons and they no longer have the outer shell.shell.

Ionic RadiusIonic Radius

Negative ionsNegative ions are are largerlarger than the neutral atom. than the neutral atom.

They get bigger They get bigger because adding because adding electrons to the outer electrons to the outer shell causes them to shell causes them to want to be want to be further apartfurther apart (like charges repel).(like charges repel).

Trends in Ionic RadiusTrends in Ionic Radius

Ionic radius increases going down and to Ionic radius increases going down and to the left.the left.

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Ionization Energy, Electron Affinity, and ElectronegativityIonization Energy, Electron Affinity, and Electronegativity

– Increases UP and to the RIGHTIncreases UP and to the RIGHT

Summary of Periodic TrendsSummary of Periodic Trends

Atomic RadiusAtomic Radius– Increases to the LEFT and DOWNIncreases to the LEFT and DOWN

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