Unit 5: PeriodicityUnit 5: Periodicity

History of the PTHistory of the PT

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

In writing a textbook of general chemistry, he compiled vast In writing a textbook of general chemistry, he compiled vast quantities of data on the elements. He realized as he examined quantities of data on the elements. He realized as he examined the data that the chemical properties of the elements repeated the data that the chemical properties of the elements repeated themselves when the elements were placed in order of atomic themselves when the elements were placed in order of atomic mass. Based on his realization, Mendeleev arranged the mass. Based on his realization, Mendeleev arranged the elements elements in order of increasing atomic massin order of increasing atomic mass, and in such a way , and in such a way that elements with similar chemical properties fell in the same that elements with similar chemical properties fell in the same column. He published a primitive version of today’s periodic column. He published a primitive version of today’s periodic table in table in 18691869. It contained the . It contained the 62 elements62 elements that had been that had been discovered at that time. discovered at that time.

Genius of Mendeleev’s WorkGenius of Mendeleev’s Work

Left spaces for Left spaces for elements not yet elements not yet discovered.discovered.

He predicted that He predicted that some still-unknown some still-unknown elements must exist to elements must exist to fit in the holes.fit in the holes.

Dmitri MendeleevDmitri Mendeleev (1869) (1869)

http://www.chem.msu.su/eng/misc/mendeleev/welcome.html

Inductive vs. Deductive ReasoningInductive vs. Deductive Reasoning

Inductive reasoningInductive reasoning is the use of detailed is the use of detailed facts to form a general principle or model facts to form a general principle or model (going from specific to general). (going from specific to general). How did How did Mendeleev use inductive reasoning?Mendeleev use inductive reasoning?

Deductive reasoningDeductive reasoning is the use of a is the use of a general principle or model to draw specific general principle or model to draw specific inferences (going from general to specific). inferences (going from general to specific). How did Mendeleev use deductive How did Mendeleev use deductive reasoning?reasoning?

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

Henry MoseleyHenry Moseley Shortly after Rutherford’s discovery of the Shortly after Rutherford’s discovery of the

proton in 1911, proton in 1911, Henry MoseleyHenry Moseley (1887-1915) (1887-1915) did experiments with x-rays to determine the did experiments with x-rays to determine the number of protons in various elements. number of protons in various elements. When Moseley arranged the elements of When Moseley arranged the elements of Mendeleev’s periodic table according to Mendeleev’s periodic table according to increasing increasing atomic numberatomic number and not atomic and not atomic mass, the mass, the inconsistencies associatedinconsistencies associated with with Mendeleev's table were Mendeleev's table were eliminated.eliminated. The The modern periodic table is based on Moseley's modern periodic table is based on Moseley's arrangement by atomic number. At age 28, arrangement by atomic number. At age 28, Moseley was killed in action during World Moseley was killed in action during World War I. As a direct result, Britain adopted the War I. As a direct result, Britain adopted the policy of exempting scientists from fighting in policy of exempting scientists from fighting in wars.wars.

Periodic LawPeriodic Law

From Mendeleev’s and Moseley’s work comes the From Mendeleev’s and Moseley’s work comes the Periodic LawPeriodic Law: The properties of the elements are : The properties of the elements are periodic functions of their periodic functions of their atomic numbersatomic numbers. .

What this means is that if we arrange the elements What this means is that if we arrange the elements in in order of increasing atomic numberorder of increasing atomic number, we will , we will periodically encounter elements that have similar periodically encounter elements that have similar chemical and physical properties. chemical and physical properties. These elements These elements appear in the same vertical column (group).appear in the same vertical column (group).

ElementsElements

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

Scientists have identified Scientists have identified 90 naturally occurring 90 naturally occurring elements, and created elements, and created about 28 others.about 28 others.

Periodic TablePeriodic Table The periodic table organizes the elements in a The periodic table organizes the elements in a

particular way. A great deal of information about an particular way. A great deal of information about an element can be gathered from its position in the element can be gathered from its position in the period table.period table.

For example, you can predict with reasonably good For example, you can predict with reasonably good accuracy the physical and chemical properties of the accuracy the physical and chemical properties of the element. You can also predict what other elements element. You can also predict what other elements a particular element will react with chemically.a particular element will react with chemically.

Understanding the organization and plan of the Understanding the organization and plan of the periodic table will help you obtain basic information periodic table will help you obtain basic information about each of the 118 known elements.about each of the 118 known elements.

Key to the Periodic TableKey to the Periodic Table Elements are organized on Elements are organized on

the table according to their the table according to their atomic number, usually found atomic number, usually found near the top of the square.near the top of the square.– The atomic number refers The atomic number refers

to how many protons an to how many protons an atom of that element has.atom of that element has.

– For instance, hydrogen For instance, hydrogen has 1 proton, so it’s has 1 proton, so it’s atomic number is 1.atomic number is 1.

– The atomic number is The atomic number is unique to that element. No unique to that element. No two elements have the two elements have the same atomic number.same atomic number.

What’s in a square?What’s in a square?

Different periodic tables Different periodic tables can include various bits can include various bits of information, but of information, but usually:usually:– atomic numberatomic number– symbolsymbol– atomic massatomic mass– number of valence number of valence

electronselectrons– state of matter at state of matter at

room temperature.room temperature.

Periodic Table Expanded ViewPeriodic Table Expanded ViewThe way the periodic table usually The way the periodic table usually seen is a compress view, placing the seen is a compress view, placing the Lanthanides and actinides at the Lanthanides and actinides at the bottom of the stable.bottom of the stable.

The Periodic Table can be arrange by The Periodic Table can be arrange by sublevels. The s-block is Group I and & 2, sublevels. The s-block is Group I and & 2, the p-block is Group 13 - 18. The d-block the p-block is Group 13 - 18. The d-block is the transition metals, and the f-block are is the transition metals, and the f-block are the Lanthanides and Actinide metalsthe Lanthanides and Actinide metals

Valence ElectronsValence Electrons The number of valence The number of valence

electrons an atom has electrons an atom has may also appear in a may also appear in a square.square.

Valence electrons are the Valence electrons are the electrons in the outer electrons in the outer energy level of an atom.energy level of an atom.

These are the electrons These are the electrons that are transferred or that are transferred or shared when atoms bond shared when atoms bond together.together.

Metals

NonmetalsMetalloids

Properties of MetalsProperties of Metals Metals are good conductors Metals are good conductors

of heat and electricity.of heat and electricity. Metals are shiny.Metals are shiny. Metals are ductile (can be Metals are ductile (can be

stretched into thin wires).stretched into thin wires). Metals are malleable (can Metals are malleable (can

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

A chemical property of metal A chemical property of metal is its reaction with water is its reaction with water which results in corrosion.which results in corrosion.

Properties of Non-MetalsProperties of Non-Metals Non-metals are poor Non-metals are poor

conductors of heat and conductors of heat and electricity.electricity.

Non-metals are not Non-metals are not ductile or malleable.ductile or malleable.

Solid non-metals are Solid non-metals are brittle and break easily.brittle and break easily.

They are dull.They are dull. Many non-metals are Many non-metals are

gases.gases.

Sulfur

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

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

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

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

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

Silicon

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

Elements in each family have Elements in each family have similar but not identical similar but not identical properties.properties.

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

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

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

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

active solid. The last element in a period, is always an active solid. The last element in a period, is always an inactive gas.inactive 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. Hydrogen is it is not a member of that family. 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 only needs 2 electrons to fill up its Hydrogen only needs 2 electrons to fill up its

valence shell.valence shell.

Alkali MetalsAlkali Metals The alkali family is found in The alkali family is found in

the first column of the the first column of the periodic table.periodic table.

Atoms of the alkali metals Atoms of the alkali metals have a single electron in have a single electron in their outermost level, in their outermost level, in other words, 1 valence other words, 1 valence electron.electron.

They are shiny, have the They are shiny, have the consistency of clay, and consistency of clay, and are easily cut with a knife.are easily cut with a knife.

Alkali MetalsAlkali Metals

They are the most They are the most reactive metals.reactive metals.

They react violently They react violently with water.with water.

Alkali metals are never Alkali metals are never found as free elements found as free elements in nature. They are in nature. They are always bonded with always bonded with another element.another element.

Alkaline Earth MetalsAlkaline Earth Metals

They are never found uncombined in nature.They are never found uncombined in nature. They have two valence electrons.They have two valence electrons. Alkaline earth metals include magnesium and Alkaline earth metals include magnesium and

calcium, among others.calcium, among others.

Transition MetalsTransition Metals

Transition Elements Transition Elements include those elements in include those elements in the B families.the B families.

These are the metals you These are the metals you are probably most familiar: are probably most familiar: copper, tin, zinc, iron, copper, tin, zinc, iron, nickel, gold, and silver.nickel, gold, and silver.

They are good conductors They are good conductors of heat and electricity.of heat and electricity.

Transition MetalsTransition Metals The compounds of The compounds of

transition metals are transition metals are usually brightly usually brightly colored and are colored and are often used to color often used to color paints.paints.

Transition elements Transition elements have 1 or 2 valence have 1 or 2 valence electrons, which electrons, which they lose when they they lose when they form bonds with form bonds with other atoms. Some other atoms. Some transition elements transition elements can lose electrons in can lose electrons in their next-to-their next-to-outermost level.outermost level.

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 oxides. oxides.

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.

Atoms in this family have 3 Atoms in this family have 3 valence electrons.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

Atoms of this family have 4 Atoms of this family have 4 valence electrons.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 compounds devoted to carbon compounds called organic chemistry.called organic 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.

Atoms in the nitrogen family Atoms in the nitrogen family have 5 valence electrons. have 5 valence electrons. They tend to share electrons They tend to share electrons when they bond.when they 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 Atoms of this family have Atoms of this family have

6 valence electrons.6 valence electrons. Most elements in this Most elements in this

family share electrons family share 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 The elements in this The elements in this

family are fluorine, family are fluorine, chlorine, bromine, iodine, chlorine, bromine, iodine, and astatine.and astatine.

Halogens have 7 valence Halogens have 7 valence electrons, which explains electrons, which explains why they are the most why they are the most active non-metals. They active non-metals. They are never found free in are never found free in nature.nature.

Halogen atoms only need Halogen atoms only need to gain 1 electron to fill to gain 1 electron to fill their outermost energy their 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 outermost because their outermost energy level is full. energy level is full.

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

The family of noble gases The family of noble gases includes helium, neon, argon, includes helium, neon, argon, krypton, xenon, and radon. krypton, xenon, and radon.

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

Is 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

Video

Electron ShieldingElectron ShieldingShielding electrons: electrons in the energy levels between the nucleus and the valence electrons. They are called "shielding" electrons because they "shield" the valence electrons from the force of attraction exerted by the positive charge in the nucleus.

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 center distance from center of nucleus to edge of electron cloudof nucleus to edge of electron cloud

group trendgroup trend:: increasesincreases going down going down a group. a group. – As you move down a group, energy As you move down a group, energy

levels are added, thus increasing the levels are added, thus increasing the size of the electron cloud, so the atoms size of the electron cloud, so the atoms get larger.get larger.

periodic trendperiodic trend:: decreasesdecreases going going left left to rightto right across a period. across a period.– [NOTE: from now on, [NOTE: from now on, “across a “across a

period”period” will refer to the will refer to the left-to-rightleft-to-right direction]direction]

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Atomic RadiusAtomic Radius

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

Atomic RadiusAtomic Radius

Atomic RadiusAtomic Radius

Trends in Ionization EnergyTrends in Ionization Energy

ionization energyionization energy:: the measure of the energy required to the measure of the energy required to removeremove an electron from the outermost energy level of an an electron from the outermost energy level of an atom. atom.

group trendgroup trend:: decreasesdecreases going down a group going down a group– This is due to the shielding effect - an electron in the outer energy This is due to the shielding effect - an electron in the outer energy

level of a large atom is easier to remove because it is well-shielded level of a large atom is easier to remove because it is well-shielded from the pull of the nucleus by the inner electrons.from the pull of the nucleus by the inner electrons.

periodic trendperiodic trend:: increasesincreases going across a period going across a period– This is due to nuclear charge - across a period, nuclear charge This is due to nuclear charge - across a period, nuclear charge

increases, so it becomes more difficult to remove an electron (held increases, so it becomes more difficult to remove an electron (held tighter).tighter).

– Note that this periodic trend supports the idea that Note that this periodic trend supports the idea that metalsmetals have a have a much greater tendency to much greater tendency to lose electronslose electrons than nonmetals do. than nonmetals do.

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First Ionization EnergyFirst Ionization 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. – *If energy is *If energy is releasedreleased in the process of adding an electron, EA is in the process of adding an electron, EA is negativenegative.. A A

negative EA means that the atom negative EA means that the atom wantswants to gain the electron. The larger the negative to gain the electron. The larger the negative number, the more it wants to gain the electron. It is a favorable process. number, the more it wants to gain the electron. It is a favorable process. Nonmetal atoms have large negative EAs.

– *If energy is *If energy is absorbedabsorbed in the process of adding an electron, EA is in the process of adding an electron, EA is positivepositive. A . A positive EA means that the atom positive EA means that the atom does not wantdoes not want to gain the electron. The larger the to gain the electron. The larger the positive number, the more it does not want to gain the electron. It is an unfavorable positive number, the more it does not want to gain the electron. It is an unfavorable process. process. Metal atoms have small negative or positive EAs.

group trendgroup trend:: EA EA decreasesdecreases (less favorable/value is more +)(less favorable/value is more +) going going down a group. down a group. – It is harder to add the electron when it is farther from the nucleus. The nucleus can’t It is harder to add the electron when it is farther from the nucleus. The nucleus can’t

“grab onto it” as well“grab onto it” as well

periodic trendperiodic trend:: EA EA increasesincreases (more favorable/value is (more favorable/value is more - ) going across a period.more - ) going across a period.– This is due to nuclear charge - across a period, nuclear charge increases, so it This is due to nuclear charge - across a period, nuclear charge increases, so it

becomes easier to add an electron.becomes easier to add an electron.– Note that this periodic trend supports the idea that Note that this periodic trend supports the idea that nonmetalsnonmetals have a much greater have a much greater

tendency to tendency to gaingain electrons than metals do electrons 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 atom to the tendency of an atom to attract attract

electronselectrons to itself when it is chemically bonded with another to itself when it is chemically bonded with another element. element. – numerical scale which combines both ionization energy and electron numerical scale which combines both ionization energy and electron

affinity.affinity.– can be used to predict whether atoms will form ionic or covalent can be used to predict whether atoms will form ionic or covalent

bonds in molecules.bonds in molecules. Diagram of water molecule:Diagram of water molecule:

– In HIn H22O, oxygen is more electronegative than hydrogen, so it pulls O, oxygen is more electronegative than hydrogen, so it pulls the electrons closer, and thus obtains a partially negative charge. the electrons closer, and thus obtains a partially negative charge.

group trendgroup trend:: decreasesdecreases down a group. down a group.– Larger atoms have more energy levels, so it is harder for them to Larger atoms have more energy levels, so it is harder for them to

attract electrons to the nucleus (shielding effect).attract electrons to the nucleus (shielding effect). periodic trendperiodic trend:: increasesincreases across a period. across a period.

– Nonmetallic character increases across a period, and nonmetals Nonmetallic character increases across a period, and nonmetals attract electrons more than metals do.attract electrons more than metals do.

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

ElectronegativityElectronegativity

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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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IE EA EN

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