Chapter 5 – The Periodic Law

Chapter 5 – The Periodic LawChapter 5 – The Periodic Law

Chuck Norris destroyed the periodic table, Chuck Norris destroyed the periodic table, because he only recognizes the element of because he only recognizes the element of surprise.surprise.

Some people are REALLY into the elements.Some people are REALLY into the elements.

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The Periodic Table…so farThe Periodic Table…so far

Displays the known elements in order of Displays the known elements in order of increasing atomic numberincreasing atomic number

Arrangement is related to electron Arrangement is related to electron configurations of elementsconfigurations of elements

Horizontal rows are periods (energy Horizontal rows are periods (energy levels)levels)

Vertical columns are groups or families Vertical columns are groups or families (similar properties)(similar properties)

The periodic table also…The periodic table also…

Allows us to predict the properties of Allows us to predict the properties of elements. elements.

Helps us to understand the chemical Helps us to understand the chemical behavior of elements. behavior of elements.

Allows us to detect trends in the properties Allows us to detect trends in the properties of the elements.of the elements.

Shows us that chemical properties are Shows us that chemical properties are predictable. predictable.

5-1 History of the Periodic Table5-1 History of the Periodic Table Dmitri Mendeleev, Dmitri Mendeleev,

Russian chemist – hoped Russian chemist – hoped to organize the known to organize the known elements according to elements according to their propertiestheir properties

At the time (1800s), At the time (1800s), nothing was known about nothing was known about the structure of the the structure of the nucleus. nucleus.

Mendeleev put elements Mendeleev put elements with their properties on with their properties on cards, arranged them cards, arranged them according to their according to their properties, and looked for properties, and looked for patternspatterns

5-1 Mendeleev and Chemical Periodicity5-1 Mendeleev and Chemical Periodicity

Noticed that when Noticed that when elements placed in elements placed in order of increasing order of increasing atomic mass, certain atomic mass, certain similarities appeared similarities appeared at regular intervalsat regular intervals

Repeating pattern is Repeating pattern is called PERIODICcalled PERIODIC

Published the first Published the first periodic table in 1869periodic table in 1869

5-1 Mendeleev’s Periodic Table5-1 Mendeleev’s Periodic Table

Left empty spaces in order to keep Left empty spaces in order to keep elements with similar properties togetherelements with similar properties together

Suggested empty spaces represented Suggested empty spaces represented elements not yet discovered AND elements not yet discovered AND predicted the properties of three predicted the properties of three undiscovered elementsundiscovered elements

by 1886, all three had been discovered – by 1886, all three had been discovered – predictions were very accuratepredictions were very accurate

Other chemists accept his arrangement.Other chemists accept his arrangement.

5-1 Mendeleev’s Periodic Table – A Problem5-1 Mendeleev’s Periodic Table – A Problem

A few elements are out of atomic mass A few elements are out of atomic mass order order

This was necessary to keep elements with This was necessary to keep elements with similar properties togethersimilar properties together

Mendeleev thought atomic masses may Mendeleev thought atomic masses may have been incorrectly measuredhave been incorrectly measured

5-1 Moseley and Atomic Number5-1 Moseley and Atomic Number

1911, English physicist 1911, English physicist Henry Moseley was working Henry Moseley was working with atomic spectra of metalswith atomic spectra of metals

Noticed elements fit into Noticed elements fit into patterns better when patterns better when arranged in order of arranged in order of increasing NUCLEAR increasing NUCLEAR CHARGECHARGE

Led to modern definition of Led to modern definition of ATOMIC NUMBER and new ATOMIC NUMBER and new basis for arrangement of basis for arrangement of periodic tableperiodic table

5-1 The Modern Periodic Table5-1 The Modern Periodic Table

An arrangement of elements in order of An arrangement of elements in order of their ATOMIC NUMBERS so that their ATOMIC NUMBERS so that elements with similar properties fall in the elements with similar properties fall in the same column or groupsame column or group

Properties repeat PERIODICALLYProperties repeat PERIODICALLY


An interactive periodic tableAn interactive periodic tableEven better interactive periodic tableEven better interactive periodic table


Noble Gases – earliest tables omitted Noble Gases – earliest tables omitted them because they hadn’t been them because they hadn’t been discovered yet (1894 – Ar, 1895 – He, discovered yet (1894 – Ar, 1895 – He, 1898 – Kr and Xe, 1900 – Rn)1898 – Kr and Xe, 1900 – Rn)

Lanthanides and Actinides – added in Lanthanides and Actinides – added in early 1900s when their properties were early 1900s when their properties were better understood – belong in periods 6 better understood – belong in periods 6 and 7, between s block and p blockand 7, between s block and p block

5-2 Electron Configuration and the Periodic Table5-2 Electron Configuration and the Periodic Table

The properties of an element are The properties of an element are determined by the electron configuration of determined by the electron configuration of the atom’s highest occupied energy level the atom’s highest occupied energy level (the valence electrons)(the valence electrons)

A filled outer energy level (s & p sublevels A filled outer energy level (s & p sublevels filled) gives an atom special stability – this filled) gives an atom special stability – this is why the noble gases are so unreactive. is why the noble gases are so unreactive.

5-1 The Periodic Table and Electron Configuration5-1 The Periodic Table and Electron Configuration

5-2 Using the Periodic Table to Determine 5-2 Using the Periodic Table to Determine Electron Configuration EndingElectron Configuration Ending

For s and p blocks: period gives energy For s and p blocks: period gives energy level, block gives sublevel, and column level, block gives sublevel, and column gives number or electronsgives number or electrons

Examples: K, Si, Rn, Cl, Sb, Sr, Mg, PExamples: K, Si, Rn, Cl, Sb, Sr, Mg, P

5-2 The s-Block Elements: Groups 1 and 25-2 The s-Block Elements: Groups 1 and 2

Chemically REACTIVE metals (group 1 > group Chemically REACTIVE metals (group 1 > group 2) 2)

Group 1: nsGroup 1: ns11, alkali metals, silvery, soft, can be , alkali metals, silvery, soft, can be cut with a knife, so reactive they are not found cut with a knife, so reactive they are not found free in nature (only in compounds)free in nature (only in compounds)

Group 2: nsGroup 2: ns22, alkaline earth metals, harder, , alkaline earth metals, harder, denser and stronger than alkali metals, higher denser and stronger than alkali metals, higher melting points, less reactive than alkali metals melting points, less reactive than alkali metals but still too reactive to be found free in naturebut still too reactive to be found free in nature

5-2 The Alkali Metals5-2 The Alkali Metals

Alkali metal reactivityAlkali metal reactivity

5-2 Alkaline Earth Metals5-2 Alkaline Earth Metals

5-2 Hydrogen and Helium5-2 Hydrogen and Helium

Special casesSpecial casesHydrogen: 1sHydrogen: 1s11, but is NOT an alkali metal , but is NOT an alkali metal

– it is a nonmetal and a gas at room – it is a nonmetal and a gas at room temperaturetemperature

Helium: 1sHelium: 1s22, placed with noble gases , placed with noble gases because of its properties (unreactive gas), because of its properties (unreactive gas), has a filled outer energy level with only 2 has a filled outer energy level with only 2 electrons (1electrons (1stst energy level only holds 2 energy level only holds 2 electrons)electrons)

5-2 The d-Block Elements: Groups 3-125-2 The d-Block Elements: Groups 3-12

For energy level n, there are n For energy level n, there are n possible sublevels, so n=3 has 3 possible sublevels, so n=3 has 3 sublevelssublevels

Because 3d has higher energy Because 3d has higher energy than 4s, the d-block first appears than 4s, the d-block first appears in the 4in the 4thth period period

ns(n-1)dns(n-1)d Transition metals – metals with Transition metals – metals with

typical metallic properties, good typical metallic properties, good conductors of heat and conductors of heat and electricity, high luster, less electricity, high luster, less reactive than s-block metals, reactive than s-block metals, some so unreactive they exist in some so unreactive they exist in nature as free elements, nature as free elements, palladium, platinum and gold are palladium, platinum and gold are least reactiveleast reactive

5-2 Exceptions to the Aufbau 5-2 Exceptions to the Aufbau PrinciplePrinciple

Atoms with a filled or half-filled sublevel Atoms with a filled or half-filled sublevel have special stabilityhave special stability

Some d-block elements have unusual Some d-block elements have unusual electron configurations that reflect this factelectron configurations that reflect this fact

Cr, CuCr, Cu

5-2 The p-Block Elements – Groups 13-185-2 The p-Block Elements – Groups 13-18

Electrons only add to p sublevel once s is filled, Electrons only add to p sublevel once s is filled, so all p-block elements have 2 electrons in ns.so all p-block elements have 2 electrons in ns.

Along with s-block elements, p-block elements Along with s-block elements, p-block elements are called MAIN-GROUP ELEMENTS.are called MAIN-GROUP ELEMENTS.

Number of valence electrons = group # - 10Number of valence electrons = group # - 10 Properties vary greatly – metals (8), metalloids Properties vary greatly – metals (8), metalloids

(6) and nonmetals (including halogens and noble (6) and nonmetals (including halogens and noble gases)gases)

5-2 Noble Gases5-2 Noble Gases

nsns22[(n-1)d[(n-1)d1010]np]np66

Have an octet (a filled s and p Have an octet (a filled s and p sublevel in their highest energy sublevel in their highest energy level) level)

Have 8 valence electrons, filled Have 8 valence electrons, filled outer energy levelouter energy level

Helium is an exception – has a Helium is an exception – has a filled outer energy level with filled outer energy level with only 2 electronsonly 2 electrons

Stable and inert (unreactive)Stable and inert (unreactive)

5-2 Halogens5-2 Halogens

Group 17: Group 17: fluorine, chlorine, fluorine, chlorine, bromine, iodine, bromine, iodine, astatine)astatine)

““Salt forming”Salt forming” Most reactive Most reactive

nonmetalsnonmetals F, Cl – gases at F, Cl – gases at

RT, Br – liquid at RT, Br – liquid at RT, I – solid at RTRT, I – solid at RT

5-2 Metalloids5-2 Metalloids

Semiconducting Semiconducting elementselements

Mostly brittle solids Mostly brittle solids with some metallic with some metallic properties and some properties and some nonmetallic propertiesnonmetallic properties

Intermediate Intermediate conductivityconductivity

Top – As, bottom - SiTop – As, bottom - Si

5-2 p-Block Metals5-2 p-Block Metals

Harder and denser Harder and denser than s-block metals than s-block metals but softer and less but softer and less dense than d-block dense than d-block metalsmetals

Reactive – only found Reactive – only found in nature in in nature in compounds (except compounds (except Bi)Bi)

Once obtained as free Once obtained as free metals, stable in airmetals, stable in air

Top – Pb, bottom – BiTop – Pb, bottom – Bi

5-3 Electron Configuration and 5-3 Electron Configuration and Periodic PropertiesPeriodic Properties

Atomic Radius – distance from the center of the Atomic Radius – distance from the center of the nucleus to the outer edge of the electron cloudnucleus to the outer edge of the electron cloud

OR ½ the distance between the nuclei of two OR ½ the distance between the nuclei of two identical atoms that are bonded togetheridentical atoms that are bonded together

5-3 Trends in Atomic Radii5-3 Trends in Atomic Radii

L to R across a period – atomic radius L to R across a period – atomic radius decreases due to increasing nuclear decreases due to increasing nuclear charge charge

Elements in a period have outermost Elements in a period have outermost electrons in same energy level so might electrons in same energy level so might predict about same size, but increasing predict about same size, but increasing charge of nucleus pulls electron cloud incharge of nucleus pulls electron cloud in

5-3 Trends in Atomic Radii5-3 Trends in Atomic Radii

Top to bottom down a group – atomic Top to bottom down a group – atomic radius increasesradius increases

Electrons occupy higher energy levels Electrons occupy higher energy levels located farther from nucleuslocated farther from nucleus

5-3 Atomic Radii5-3 Atomic Radii

5-3 Atomic Radius as a Function of 5-3 Atomic Radius as a Function of Atomic NumberAtomic Number

5-3 Valence Electrons and the 5-3 Valence Electrons and the Periodic TablePeriodic Table

5-3 Ions and Ion Formation5-3 Ions and Ion Formation

Ion – an atom or group of bonded atoms Ion – an atom or group of bonded atoms that has a positive or negative chargethat has a positive or negative charge

Monatomic ions form when an atom gains Monatomic ions form when an atom gains or loses an electron or electronsor loses an electron or electrons

Cations – positive ions formed by the loss Cations – positive ions formed by the loss of electronsof electrons

Anions – negative ions formed by the gain Anions – negative ions formed by the gain of electronsof electrons

5-3 The Octet Rule and Ion 5-3 The Octet Rule and Ion FormationFormation

Octet ruleOctet rule – atoms will gain, lose or share – atoms will gain, lose or share electrons in order to obtain a filled outer electrons in order to obtain a filled outer energy level (usually 8 electrons)energy level (usually 8 electrons)

Metals tend to lose electrons in order to Metals tend to lose electrons in order to gain an octetgain an octet

Nonmetals tend to gain (or share) Nonmetals tend to gain (or share) electrons in order to gain an octetelectrons in order to gain an octet

5-3 The Octet Rule: Sodium5-3 The Octet Rule: Sodium

Sodium has one Sodium has one valence electron.valence electron.

It loses one valence It loses one valence electron to reveal a electron to reveal a filled shell. filled shell.

A sodium ion has a A sodium ion has a charge of +1, Nacharge of +1, Na++..

5-3 The Octet Rule: Chlorine5-3 The Octet Rule: Chlorine

Chlorine has 7 Chlorine has 7 valence electrons. valence electrons.

It is very close to It is very close to having a filled outer having a filled outer energy level. energy level.

It will gain one It will gain one electron to fill its outer electron to fill its outer energy level. energy level.

A chloride ion has a A chloride ion has a charge of -1, Clcharge of -1, Cl--..

5-3 The Octet Rule and Ion 5-3 The Octet Rule and Ion FormationFormation In general…In general…

Atoms with 1, 2 or 3 valence electrons (metals) will lose their Atoms with 1, 2 or 3 valence electrons (metals) will lose their valence electrons, forming cations. valence electrons, forming cations.

Atoms with 5, 6 or 7 valence electrons (nonmetals) will gain Atoms with 5, 6 or 7 valence electrons (nonmetals) will gain enough electrons to complete their octet, forming anions. enough electrons to complete their octet, forming anions.

5-3 Ionization Energy5-3 Ionization Energy

Neutral atoms can lose electronsNeutral atoms can lose electrons Ionization energy, IE – energy required to Ionization energy, IE – energy required to

remove one electron from a neutral atom remove one electron from a neutral atom of an element, measured in kJ/molof an element, measured in kJ/mol

A + energy A + energy A A++ + e + e--

5-3 Trends in Ionization Energy5-3 Trends in Ionization Energy

L to R across a period – ionization energy L to R across a period – ionization energy increases - it becomes harder to remove increases - it becomes harder to remove the valence electron(s)the valence electron(s)

The closer the valence electrons are to the The closer the valence electrons are to the nucleus and the greater the nuclear nucleus and the greater the nuclear charge, the harder they are to remove – charge, the harder they are to remove – held more tightlyheld more tightly

Nonmetals have higher ionization energies Nonmetals have higher ionization energies than metalsthan metals


Top to bottom down group – ionization energy Top to bottom down group – ionization energy decreases – it becomes easier to remove the decreases – it becomes easier to remove the valence electron(s)valence electron(s)

Electrons removed from each successive Electrons removed from each successive element are farther from the nucleus so are held element are farther from the nucleus so are held less tightlyless tightly

More electrons lie between the nucleus and the More electrons lie between the nucleus and the valence electron(s), which partially shields the valence electron(s), which partially shields the valence electron(s) from the pull of the nucleusvalence electron(s) from the pull of the nucleus


Where on the periodic table are the elements Where on the periodic table are the elements most likely to LOSE electron?most likely to LOSE electron?

5-3 Multiple Ionization Energies5-3 Multiple Ionization Energies

Electrons can be removed from positive ions as Electrons can be removed from positive ions as well as neutral atomswell as neutral atoms

These successive IEs are names 2These successive IEs are names 2ndnd ionization ionization energy, 3energy, 3rdrd ionization energy, etc ionization energy, etc

22ndnd ionization energy is always higher than 1 ionization energy is always higher than 1stst

33rdrd ionization energy is always higher than 2 ionization energy is always higher than 2ndnd As electrons are removed, fewer electrons As electrons are removed, fewer electrons

remain to shield attractive force of nucleus, each remain to shield attractive force of nucleus, each successive electron removed feels greater successive electron removed feels greater effective nuclear chargeeffective nuclear charge

5-3 Successive Ionization Energies 5-3 Successive Ionization Energies of Selected Elements in kJ/molof Selected Elements in kJ/mol

LiLi BeBe NaNa MgMg

IEIE11 520520 900900 496496 738738

IEIE22 72987298 17571757 45624562 14511451

IEIE33 1181511815 14,84914,849 69126912 77337733

5-3 Ionization Energy 5-3 Ionization Energy

Why do you think helium has the highest first Why do you think helium has the highest first ionization energy of any element?ionization energy of any element?

5-3 Electron Affinity5-3 Electron Affinity

Neutral atoms can gain electrons.Neutral atoms can gain electrons. electron affinity – the energy change that occurs electron affinity – the energy change that occurs

when an electron is acquired by a neutral atomwhen an electron is acquired by a neutral atomA + eA + e-- A A-- + energy + energy

The quantity of energy released is represented by The quantity of energy released is represented by a negative numbera negative number

The more energy lost, the more likely an atom is to The more energy lost, the more likely an atom is to gain an electrongain an electron

A value of zero means the atom has NO tendency A value of zero means the atom has NO tendency to gain an electronto gain an electron

5-3 Trends in Electron Affinity5-3 Trends in Electron Affinity

Halogens gain electrons most readilyHalogens gain electrons most readily L to R across p block, electron affinities get more L to R across p block, electron affinities get more

negative negative Exception is between groups 14 and 15 because Exception is between groups 14 and 15 because

of stability of half-filled sublevelof stability of half-filled sublevel Adding an electron to carbon is easier than Adding an electron to carbon is easier than

adding an electron to nitrogen, which requires adding an electron to nitrogen, which requires forcing an electron to pair up in an orbital of the forcing an electron to pair up in an orbital of the already half-filled p sublevelalready half-filled p sublevel

Note noble gases have electron affinities of zero.Note noble gases have electron affinities of zero.

5-3 Trends in Electron Affinity5-3 Trends in Electron Affinity

Top to bottom down group – generally Top to bottom down group – generally decreases down a group, but there are decreases down a group, but there are some exceptionssome exceptions

Generally, as atomic radius increases, Generally, as atomic radius increases, attraction of an atom for an electron attraction of an atom for an electron decreasesdecreases

5-3 Ionization Energy, Electron 5-3 Ionization Energy, Electron Affinity and ReactivityAffinity and Reactivity

5-3 Ionic Radii5-3 Ionic Radii Cations – smaller than their respective atoms – outer Cations – smaller than their respective atoms – outer

energy level is lost and remaining electrons are drawn energy level is lost and remaining electrons are drawn closer to nucleuscloser to nucleus

5-3 Ionic Radii5-3 Ionic Radii

Anions – larger than their respective Anions – larger than their respective atoms – electron cloud spreads out atoms – electron cloud spreads out because of greater repulsion between because of greater repulsion between increased number of electronsincreased number of electrons

ElectronegativityElectronegativity

A measure of the ability of an atom in a A measure of the ability of an atom in a chemical compound to attract electronschemical compound to attract electrons

Most electronegative element, fluorine, is Most electronegative element, fluorine, is given a value of 4given a value of 4

Values of other elements are assigned Values of other elements are assigned relative to fluorinerelative to fluorine

Trends in ElectronegativityTrends in Electronegativity

L to R across a period – electronegativities L to R across a period – electronegativities tend to decreasetend to decrease

The most electronegative elements are The most electronegative elements are nitrogen, oxygen and the halogensnitrogen, oxygen and the halogens

The least electronegative elements are the The least electronegative elements are the alkali metals and the alkaline earth metalsalkali metals and the alkaline earth metals


Top to bottom down a group – Top to bottom down a group – electronegativities either decrease or electronegativities either decrease or remain about the sameremain about the same

Noble gases are unusual – some do not Noble gases are unusual – some do not form compounds so electronegativity form compounds so electronegativity cannot be measuredcannot be measured


What does electronegativity mean?What does electronegativity mean?

5-3 Polar Bonds5-3 Polar Bonds

If two atoms bonded to one another differ If two atoms bonded to one another differ greatly in their electronegativities, the greatly in their electronegativities, the electron density will be drawn to one end electron density will be drawn to one end of the bond. of the bond.

The bond has a positive end and a The bond has a positive end and a negative end. negative end.

This is a polar bond. This is a polar bond.

There are some polar bonds in a polar bear.

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Chapter 5 – The Periodic Law