Periodic LawPeriodic LawHistory of the Periodic History of the Periodic Table Table

Periodic TrendsPeriodic Trends

Mendeleev - 1869Mendeleev - 1869

Organize elements according to Organize elements according to propertiesproperties

He noticed that certain properties He noticed that certain properties appeared at regular intervalsappeared at regular intervals

He left empty spots in his table – He left empty spots in his table – he predicted that there were he predicted that there were elements that scientists did not elements that scientists did not yet know aboutyet know about

Mendeleev’s Periodic Table

Dmitri Mendeleev

Chinese Periodic Table

Stowe Periodic Table

Moseley - 1913Moseley - 1913

Slightly changed Mendeleev’s Slightly changed Mendeleev’s table table

Ordered elements according to Ordered elements according to Atomic NumberAtomic Number

Periodic LawPeriodic Law = physical and = physical and chemical properties of the chemical properties of the elements are periodic functions of elements are periodic functions of their atomic numberstheir atomic numbers

Modern Periodic TableModern Periodic Table

Arranged according to Atomic Arranged according to Atomic NumberNumber

Elements with similar properties Elements with similar properties fall in the same column (group)fall in the same column (group)

Know these four families:Know these four families:– Noble GasesNoble Gases– HalogensHalogens– Alkali Earth MetalsAlkali Earth Metals– Earth MetalsEarth Metals

Families of the Periodic Families of the Periodic TableTable Noble Gases = Group 18, Noble Gases = Group 18,

UnreactiveUnreactive Halogens = Group 17, Very Halogens = Group 17, Very

reactivereactive Alkali Metals = Group 1, Very Alkali Metals = Group 1, Very

reactivereactive Alkaline Earth Metals = Group 2, Alkaline Earth Metals = Group 2,

very reactivevery reactive

Regions of the Periodic Regions of the Periodic TableTable

Metals – to the left of the stair Metals – to the left of the stair step line step line

Nonmetals – to the right of the Nonmetals – to the right of the stair step linestair step line

Metalloids – Elements that Metalloids – Elements that border the stair step line border the stair step line (except for Al)(except for Al)

Transition metals – d blockTransition metals – d block

Main group elements – s and p Main group elements – s and p blockblock

Periodic Trends – Atomic Periodic Trends – Atomic RadiiRadii Atomic Radii – size of the atom, half the Atomic Radii – size of the atom, half the

distance between the nuclei of identical distance between the nuclei of identical atoms that are bonded togetheratoms that are bonded together

Across a period – atomic radii decreases Across a period – atomic radii decreases due to an increase in the effective due to an increase in the effective nuclear chargenuclear charge

Down a group – atomic radii increases Down a group – atomic radii increases due to addition of outermost electrons to due to addition of outermost electrons to higher energy levelshigher energy levels

Atomic RadiusAtomic Radius

0

50

100

150

200

250

0 5 10 15 20Atomic Number

Ato

mic

Ra

diu

s (

pm

)

Trends in Atomic Trends in Atomic RadiusRadius

Li

ArNe

KNa

Table of Table of

Atomic Atomic RadiiRadii

Periodic Trend – Periodic Trend – Ionization EnergyIonization Energy Ionization energy (IE) – the Ionization energy (IE) – the

amount of energy it takes to amount of energy it takes to remove an electron from a remove an electron from a neutral atomneutral atom

Ion – formed when at atom loses Ion – formed when at atom loses or gains electronsor gains electrons

Ionization – the process that Ionization – the process that results in the formation of an ionresults in the formation of an ion

Ionization energy increases across a row.Ionization energy increases across a row.– It becomes more difficult to lose valence It becomes more difficult to lose valence

electrons as you move across a row due to electrons as you move across a row due to increasing effective nuclear charge.increasing effective nuclear charge.

Ionization energy decreases down a group. Ionization energy decreases down a group. – It becomes easier to remove valence electrons It becomes easier to remove valence electrons

as you move down a group because the as you move down a group because the electrons are farther from the nucleus.electrons are farther from the nucleus. Shielding EffectShielding Effect – the inner shell electrons – the inner shell electrons

interfere with the nucleus attraction to the interfere with the nucleus attraction to the valence electrons.valence electrons.

First Ionization EnergyFirst Ionization Energy

0

500

1000

1500

2000

2500

0 5 10 15 20Atomic Number

1s

t Io

niz

ati

on

En

erg

y (k

J)

Trends in Ionization Trends in Ionization EnergyEnergy

KNaLi

Ar

NeHe

1

2

3

4 5

6

7

First Ionization EnergyFirst Ionization Energy– Increases UP and to the RIGHTIncreases UP and to the RIGHT

E. Ionization EnergyE. Ionization Energy

Electron AffinityElectron Affinity

Electron Affinity (EA) - the energy Electron Affinity (EA) - the energy change that occurs when an electron change that occurs when an electron is acquired by a neutral atomis acquired by a neutral atom

When an atom gains an electron When an atom gains an electron easily, a large amount of energy is easily, a large amount of energy is released (indicated by a high released (indicated by a high negative number). These elements negative number). These elements will have a high electron affinity.will have a high electron affinity.

Electron Affinity - Electron Affinity - TrendTrend In general, electron affinity In general, electron affinity

increases across a periodincreases across a period– Atoms accept electrons easily.Atoms accept electrons easily.

In general, electron affinity In general, electron affinity decreases down a group. decreases down a group. – Larger atoms cannot accept Larger atoms cannot accept

electrons as easily.electrons as easily.

Electron Affinities of the Elements

Why gain or lose Why gain or lose electrons?electrons? The noble gases are stable because The noble gases are stable because

they have 8 electrons in their highest they have 8 electrons in their highest energy level – energy level – a complete octeta complete octet..

The other families need to gain or lose The other families need to gain or lose electrons so they can also have a electrons so they can also have a complete octet.complete octet.

Groups 1, 2, 3 lose valence electrons to Groups 1, 2, 3 lose valence electrons to form cations – positive ions (cations).form cations – positive ions (cations).

Groups 5, 6, 7 gain electrons to form Groups 5, 6, 7 gain electrons to form anions – negative ions (anions). anions – negative ions (anions).

CationsCations

Cations lose valence electrons Cations lose valence electrons and become positive.and become positive.

To name a cation, add the To name a cation, add the word word ionion to the end of the to the end of the element name.element name.

Cations are smaller than the Cations are smaller than the original atom.original atom.

AnionsAnions

Anions gain valence electrons and Anions gain valence electrons and become negative.become negative.

To name an anion, change the To name an anion, change the ending of the element name to ending of the element name to ––ideide and add the word and add the word ionion..

Anions are larger than the original Anions are larger than the original atom.atom.

Teachers: have students label periodic tableTeachers: have students label periodic table

ElectronegativityElectronegativity

Measure of the ability of an atom Measure of the ability of an atom in a chemical compound to in a chemical compound to attract electrons.attract electrons.

Fluorine is the most Fluorine is the most electronegative element and has electronegative element and has been assigned an been assigned an electronegativity value of 4.electronegativity value of 4.

Electronegativity – Electronegativity – Periodic TrendsPeriodic Trends Across a period, electronegativity Across a period, electronegativity

increases.increases.– The halogens highly attract The halogens highly attract

electrons.electrons. Down a group, electronegativity Down a group, electronegativity

decreases.decreases.– Larger atoms do not attract Larger atoms do not attract

electrons as easily.electrons as easily.

Periodic Table of Electronegativities

Summation of Periodic Trends