chapter 6 “the periodic table” chemistry. section 6.1 organizing the elements objectives:...

Chapter 6Chapter 6

“The Periodic Table”“The Periodic Table”

ChemistryChemistry

Section 6.1Section 6.1Organizing the ElementsOrganizing the Elements

•OBJECTIVES:OBJECTIVES:

–ExplainExplain how elements are how elements are organized in a periodic organized in a periodic table.table.



–CompareCompare early and modern early and modern periodic tables.periodic tables.



– IdentifyIdentify three broad classes three broad classes of elements.of elements.


• A few elements, such as gold and A few elements, such as gold and copper, have been known for copper, have been known for thousands of yearsthousands of years - since - since ancient timesancient times

• Yet, only about 13 had been Yet, only about 13 had been identified by the year 1700.identified by the year 1700.


• DuringDuring the nineteenth century, the nineteenth century, chemists began to categorize the chemists began to categorize the elementselements according to similarities in according to similarities in their physical and chemical properties. their physical and chemical properties. The end result of these studies was our The end result of these studies was our modern periodic tablemodern periodic table..

Johann DobereinerJohann Dobereiner

• In 1829, he classified some elements In 1829, he classified some elements into groups of three, which he called into groups of three, which he called triads.The elements in a triad had triads.The elements in a triad had similar chemical properties and similar chemical properties and orderly physical properties.orderly physical properties.

• ex. Cl, Br, I andex. Cl, Br, I andCa, Sr, Ba)Ca, Sr, Ba)

Model of triads1780 - 1849

JohnJohn NewlandsNewlands

• In 1863, he suggested that elements be In 1863, he suggested that elements be arranged in “octaves” because he noticed arranged in “octaves” because he noticed (after arranging the elements in order of (after arranging the elements in order of increasing atomic mass) that certain increasing atomic mass) that certain properties repeated every 8th element.properties repeated every 8th element.

• Law of OctavesLaw of Octaves

• 1838 - 18981838 - 1898


• His law of octaves failed beyond the element His law of octaves failed beyond the element calcium. Why?calcium. Why?

• Would his law of octaves work today with Would his law of octaves work today with the first 20 elements?the first 20 elements?


Newlands' claim to see a repeating pattern was met with savage ridicule on its announcement. His classification of the elements, he was told, was as arbitrary as putting them in alphabetical order and his paper was rejected for publication by the Chemical Society.

Mendeleev’s Periodic TableMendeleev’s Periodic Table• By the mid-1800s, about 70 elements By the mid-1800s, about 70 elements

were known to existwere known to exist

• Dmitri Dmitri MendeleevMendeleev – a Russian chemist – a Russian chemist and teacherand teacher

• Arranged elements in order of Arranged elements in order of increasing increasing atomic massatomic mass

• Thus, the first “Periodic Table” Thus, the first “Periodic Table”

Mendeleev’s Periodic TableMendeleev’s Periodic Table

MendeleevMendeleev•He left blanksHe left blanks for yet for yet

undiscovered elementsundiscovered elements• stated that if the atomic weight of an stated that if the atomic weight of an

element caused it to be placed in the element caused it to be placed in the wrong group, then the weight must be wrong group, then the weight must be wrong. (He corrected the atomic wrong. (He corrected the atomic masses of Be, In, and U)masses of Be, In, and U)

• was so confident in his table that he was so confident in his table that he used it to predict the physical used it to predict the physical properties of three elements that were properties of three elements that were yet unknownyet unknown..

MendeleevMendeleev

• After the discovery of these unknown After the discovery of these unknown elements between 1874 and 1885, and the elements between 1874 and 1885, and the fact that Mendeleev’s predictions for Sc, fact that Mendeleev’s predictions for Sc, Ga, and Ge were amazingly close to the Ga, and Ge were amazingly close to the actual values, his table was generally actual values, his table was generally accepted.accepted.

MendeleevMendeleev

• However, in spite of Mendeleev’s great However, in spite of Mendeleev’s great achievement, problems arose when new achievement, problems arose when new elements were discovered and more accurate elements were discovered and more accurate atomic weights determined. By looking at our atomic weights determined. By looking at our modern periodic table, can you identify what modern periodic table, can you identify what problems might have caused chemists a problems might have caused chemists a headache?headache?

Ar and K

Co and NiTe and ITh and Pa

A better arrangementA better arrangement

•In 1913, Henry In 1913, Henry MoseleyMoseley – – British physicist, arranged British physicist, arranged elements according to elements according to increasing increasing atomic numberatomic number

•The arrangement used todayThe arrangement used today

•The symbol, atomic number The symbol, atomic number & mass are basic items & mass are basic items included-textbook page 162 included-textbook page 162 and 163and 163

Another possibility: Another possibility: Spiral Periodic TableSpiral Periodic Table

The Periodic Law says:The Periodic Law says:•When elements are arranged in When elements are arranged in

order of increasing atomic order of increasing atomic number, there is a number, there is a periodic periodic repetitionrepetition of their physical and of their physical and chemical properties.chemical properties.

•Horizontal rows = Horizontal rows = periodsperiods– There are 7 periodsThere are 7 periods

•Vertical column = Vertical column = groupgroup (or (or family)family)– Similar physical & chemical prop.Similar physical & chemical prop.– Identified by number & letter (IA, IIA)Identified by number & letter (IA, IIA)

Areas of the periodic tableAreas of the periodic table

• Three classes of elements Three classes of elements are: 1) metals, 2) are: 1) metals, 2) nonmetals, and 3) nonmetals, and 3) metalloidsmetalloids

1)1) MetalsMetals: electrical conductors, : electrical conductors, have luster, ductile, malleablehave luster, ductile, malleable

2)2) NonmetalsNonmetals: generally brittle and : generally brittle and non-lustrous, poor conductors of non-lustrous, poor conductors of heat and electricityheat and electricity

Areas of the periodic tableAreas of the periodic table• Some nonmetals are gases (O, Some nonmetals are gases (O,

N, Cl); some are brittle solids N, Cl); some are brittle solids (S); one is a fuming dark red (S); one is a fuming dark red liquid (Br)liquid (Br)

• Notice the heavy, stair-step Notice the heavy, stair-step line?line?

3)3) MetalloidsMetalloids: border the line-2 : border the line-2 sidessides

– Properties are Properties are intermediateintermediate between metals and nonmetalsbetween metals and nonmetals

Section 6.2Section 6.2Classifying the ElementsClassifying the Elements


–DescribeDescribe the information the information in a periodic table.in a periodic table.



–ClassifyClassify elements based elements based on electron configuration.on electron configuration.



–DistinguishDistinguish representative elements representative elements and transition metals.and transition metals.

Squares in the Periodic TableSquares in the Periodic Table

•The periodic table displays The periodic table displays the the symbolssymbols and and namesnames of of the elements, along with the elements, along with information about the information about the structure of their atoms:structure of their atoms:•Atomic number and atomic massAtomic number and atomic mass•Black symbol = solidBlack symbol = solid; ; red = red = gasgas; ; blue = liquid blue = liquid (from the Periodic Table on our (from the Periodic Table on our classroom wall)classroom wall)

Groups of elements Groups of elements - family names- family names

•Group 1Group 1 – – alkali metalsalkali metals– Forms a “base” (or alkali) when Forms a “base” (or alkali) when

reactingreacting with water with water (not just dissolved!) (not just dissolved!)

•Group 2Group 2 – – alkaline earth alkaline earth metalsmetals– Also form bases with water; do not Also form bases with water; do not

dissolve well, hence “earth metals”dissolve well, hence “earth metals”

•Group 17Group 17 – – halogenshalogens– Means “salt-forming”Means “salt-forming”

Electron Configurations in GroupsElectron Configurations in Groups

• Elements can be sorted Elements can be sorted into 4 different into 4 different groupings groupings based on their based on their electron configurationselectron configurations::

1)1) Noble gasesNoble gases2)2) Representative elementsRepresentative elements

3)3) Transition metalsTransition metals

4)4) Inner transition metalsInner transition metals

Let’s now take a closer look at these.


1)1) Noble gasesNoble gases are the are the elements in Group 18elements in Group 18

• Previously called “Previously called “inert gasesinert gases” ” because they rarely take part in because they rarely take part in a reaction; a reaction; very stablevery stable = don’t = don’t reactreact

• Noble gases have an electron Noble gases have an electron configuration that has the outer configuration that has the outer s and p sublevels s and p sublevels completely fullcompletely full


2)2) Representative ElementsRepresentative Elements are are in Groups 1and 2 then 13 in Groups 1and 2 then 13 to 17to 17

• Display Display wide rangewide range of properties, of properties, thus a good “representative” thus a good “representative”

• Some are metals, or nonmetals, or Some are metals, or nonmetals, or metalloids; some are solid, others metalloids; some are solid, others are gases or liquidsare gases or liquids

• Their outer s and p electron Their outer s and p electron configurations are configurations are NOT filledNOT filled


3)3) Transition metalsTransition metals are in are in the Block between the Block between groups 2 and 13 groups 2 and 13

4)4) Electron configuration has the Electron configuration has the outer s sublevel full, and is now outer s sublevel full, and is now filling the “filling the “d” subleveld” sublevel

• A “transition” between the metal A “transition” between the metal area and the nonmetal areaarea and the nonmetal area

• Examples are gold, copper, silverExamples are gold, copper, silver


4)4) Inner Transition MetalsInner Transition Metals are are located below the main located below the main body of the table, in two body of the table, in two horizontal rowshorizontal rows

• Electron configuration has the Electron configuration has the outer s sublevel full, and is now outer s sublevel full, and is now filling the filling the “f” sublevel“f” sublevel

• Formerly called “rare-earth” Formerly called “rare-earth” elements, but this is not true elements, but this is not true because some are very abundantbecause some are very abundant

1

2 13 14 15 16 17

18• Elements in the 1and 2 13-Elements in the 1and 2 13-17 groups are called the 17 groups are called the representative elementsrepresentative elements

outer s or p fillingouter s or p filling

The The group B group B are called the are called the transition elementstransition elements

These are called the inner transition elements, and they belong here

Group 1 are the alkali metals Group 1 are the alkali metals (but NOT H)(but NOT H)

Group 2 are the alkaline earth metalsGroup 2 are the alkaline earth metalsH

• Group 18 are the Group 18 are the noble gasesnoble gases

• Group 17 is called the Group 17 is called the halogenshalogens

11ss11

1s1s2222ss11

1s1s222s2s222p2p6633ss11

1s1s222s2s222p2p663s3s223p3p6644ss11

1s1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p6655ss11

1s1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p665s5s2244dd10 10 5p5p6666ss11

1s1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p665s5s2244dd10105p5p666s6s224f4f14145d5d10106p6p6677ss11

H1

Li3

Na11

K19

Rb37

Cs55

Fr87

Do you notice any similarity in these configurations of the alkali metals?

He2

Ne10

Ar18

Kr36

Xe54

Rn86

11ss22

1s1s222s2s222p2p66

1s1s222s2s222p2p663s3s223p3p66

1s1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p66

1s1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p665s5s224d4d10105p5p66

1s1s222s2s222p2p663s3s223p3p664s4s223d3d10104p4p665s5s224d4d10 10

5p5p666s6s224f4f14145d5d10106p6p66

Do you notice any similarity in the configurations of the noble gases?

• Alkali metals all end in Alkali metals all end in ss11

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

– really should include He, but it really should include He, but it fits better in a different spot, fits better in a different spot, since He has the properties of the since He has the properties of the noble noble gasesgases, and has a full outer , and has a full outer level of electrons.level of electrons.

s2s1Elements in the s - blocksElements in the s - blocks

He

Transition Metals - d blockTransition Metals - d block

d1 d2 d3s1

d5 d5 d6 d7 d8s1

d10 d10

Note the change in configuration.

The P-blockThe P-blockp1 p2 p3 p4 p5 p6

F - blockF - block

• Called the “inner transition Called the “inner transition elements”elements”

f1 f5f2 f3 f4

f6 f7 f8 f9 f10 f11 f12 f14

f13

• Each row (or period) is the Each row (or period) is the energy energy levellevel for s and p orbitals. for s and p orbitals.

1

2

3

4

5

6

7

Period Number

• The “d” orbitals fill up in levels The “d” orbitals fill up in levels 1 less1 less than the period number, so the first d is than the period number, so the first d is 3d even though it’s in row 4.3d even though it’s in row 4.

1

2

3

4

5

6

7

3d

4d5d

• f orbitals start filling at 4f, and are f orbitals start filling at 4f, and are 2 2 lessless than the period number than the period number

1

2

3

4

5

6

7 4f

5f

Section 6.3Section 6.3Periodic TrendsPeriodic Trends


–DescribeDescribe trendstrends among the among the elements for elements for atomic sizeatomic size..



–ExplainExplain how how ionsions form. form.



–DescribeDescribe periodic periodic trendstrends for for first ionization energy, ionic first ionization energy, ionic size, and electronegativity.size, and electronegativity.

Trends in Atomic SizeTrends in Atomic Size

•First problem: Where do you First problem: Where do you start measuring from?start measuring from?

•The electron cloud doesn’t have The electron cloud doesn’t have a definite edge.a definite edge.

•They get around this by They get around this by measuring more than 1 atom at measuring more than 1 atom at a time.a time.

Atomic SizeAtomic Size

•Measure the Atomic Radius - this is half the Measure the Atomic Radius - this is half the distance between the two nuclei of a diatomic distance between the two nuclei of a diatomic molecule.molecule.

}Radius

ALLALL Periodic Table Trends Periodic Table Trends • Influenced by three factors:Influenced by three factors:

1. 1. Energy LevelEnergy Level– Higher energy levels are further Higher energy levels are further

away from the nucleus.away from the nucleus.

2. 2. Charge on nucleusCharge on nucleus (# protons) (# protons)– More charge pulls electrons in More charge pulls electrons in

closer. (+ and – attract each other)closer. (+ and – attract each other)

•3. 3. Shielding effectShielding effect(blocking effect?)

What do they influence?What do they influence?

Energy levelsEnergy levels and and

ShieldingShielding have an effect have an effect

on the on the GROUPGROUP ( ( ) )

Nuclear chargeNuclear charge has an has an

effect on a effect on a PERIODPERIOD ( ( ) )

#1. #1. Atomic SizeAtomic Size - Group trends - Group trends• As we increase As we increase

the atomic the atomic number (or go number (or go down a down a group). . .group). . .

• each atom has each atom has another energy another energy level,level,

• so the atoms get so the atoms get

biggerbigger..

HLi

Na

K

Rb

#1. #1. Atomic SizeAtomic Size - Period Trends - Period Trends• Going from left to right across a period, Going from left to right across a period,

the size the size getsgets smallersmaller..

• Electrons are in the Electrons are in the same energy levelsame energy level..

• But, there is more But, there is more nuclear chargenuclear charge..

• Outermost electrons are pulled closer.Outermost electrons are pulled closer.

Na Mg Al Si P S Cl Ar

Atomic Number

Ato

mic

Rad

ius

(pm

)

H

Li

Ne

Ar

10

Na

K

Kr

Rb

3

Period 2

IonsIons•Some compounds are Some compounds are

composed of particles called composed of particles called “ions”“ions”– An An ionion is an atom (or group of atoms) is an atom (or group of atoms)

that has a that has a positive or negative chargepositive or negative charge

• AtomsAtoms are neutral because the are neutral because the number of protons equals electronsnumber of protons equals electrons– Positive and negative ions are formed Positive and negative ions are formed

when electrons are when electrons are transferredtransferred (lost or (lost or gained) between atomsgained) between atoms

IonsIons•Metals tend to LOSE Metals tend to LOSE

electronselectrons, from their outer , from their outer energy levelenergy level– Sodium loses one: there are now Sodium loses one: there are now

more protons (11) than electrons more protons (11) than electrons (10), and thus a positively charged (10), and thus a positively charged particle is formed = “particle is formed = “cationcation””

– The charge is written as a number The charge is written as a number followed by a plus sign: Nafollowed by a plus sign: Na1+1+

– Now named a “Now named a “sodium ionsodium ion””

IonsIons

•Nonmetals tend to GAINNonmetals tend to GAIN one or more electronsone or more electrons– Chlorine will gain one electronChlorine will gain one electron– Protons (17) no longer equals the Protons (17) no longer equals the

electrons (18), so a charge of -1electrons (18), so a charge of -1– ClCl1-1- is re-named a “chloride ion” is re-named a “chloride ion”– Negative ions are called “Negative ions are called “anionsanions””

#2. Trends in Ionization Energy#2. Trends in Ionization Energy

• Ionization energy is the amount of Ionization energy is the amount of energy required to energy required to completely completely remove an electronremove an electron (from a gaseous (from a gaseous atom).atom).

•Removing one electron makes a 1+ Removing one electron makes a 1+ ion.ion.

•The energy required to remove only The energy required to remove only the first electron is called the the first electron is called the firstfirst ionization energy.ionization energy.

Ionization EnergyIonization Energy

•TheThe second second ionization energy is ionization energy is the energy required to remove the the energy required to remove the second electron.second electron.– Always greater than first IE.Always greater than first IE.

•The The thirdthird IE is the energy required IE is the energy required to remove a third electron.to remove a third electron.– Greater than 1st or 2nd IE.Greater than 1st or 2nd IE.

Symbol First Second ThirdHHeLiBeBCNO F Ne

1312 2731 520 900 800 1086 1402 1314 1681 2080

5247 7297 1757 2430 2352 2857 3391 3375 3963

11810 14840 3569 4619 4577 5301 6045 6276

Table 6.1, p. 173

Symbol First Second ThirdHHeLiBeBCNO F Ne

1312 2731 520 900 800 1086 1402 1314 1681 2080

5247 7297 1757 2430 2352 2857 3391 3375 3963

11810 14840 3569 4619 4577 5301 6045 6276

Why did these values increase so much?

What factors determine IEWhat factors determine IE

•The greater the nuclear charge, the The greater the nuclear charge, the greatergreater IE. IE.

•Greater distance from nucleus Greater distance from nucleus decreasesdecreases IE IE

•Filled and half-filled orbitals have Filled and half-filled orbitals have lower energy, so achieving them is lower energy, so achieving them is easier, lower IE.easier, lower IE.

•Shielding effectShielding effect

ShieldingShielding

• The electron on the The electron on the outermost energy level outermost energy level has to look through all has to look through all the other energy levels the other energy levels to see the nucleus.to see the nucleus.

• Second electron has Second electron has samesame shielding, if it is shielding, if it is in the in the same periodsame period

Ionization Energy - Group trendsIonization Energy - Group trends

•As you go down a group, As you go down a group, the first IE decreases the first IE decreases because...because...–The electron is further The electron is further away from the attraction away from the attraction of the nucleus, andof the nucleus, and

–There is more shielding.There is more shielding.

Ionization Energy - Period trendsIonization Energy - Period trends

•All the atoms in the same period have All the atoms in the same period have the same energy level.the same energy level.

•Same shielding.Same shielding.

•But, increasing nuclear chargeBut, increasing nuclear charge

•So IE generally So IE generally increasesincreases from left to from left to right.right.

•Exceptions at full and 1/2 full orbitals.Exceptions at full and 1/2 full orbitals.

Firs

t Ion

izat

ion

ener

gy

Atomic number

He •He has a greater IE He has a greater IE than H.than H.

•Both elements have Both elements have the same shielding the same shielding since electrons are since electrons are only in the first level only in the first level

•But He has a greater But He has a greater nuclear chargenuclear charge

H

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Li has lower IE than H

more shielding further away These outweigh

the greater nuclear charge

Li

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Be has higher IE than Li

same shielding greater nuclear

charge

Li

Be

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He B has lower IE

than Be same shielding greater nuclear

charge By removing an

electron we make s orbital half-filled

Li

Be

B

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Li

Be

B

C

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Li

Be

B

C

N

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Li

Be

B

C

N

O

•Oxygen breaks Oxygen breaks the pattern, the pattern, because because removing an removing an electron leaves electron leaves it with a 1/2 it with a 1/2 filled p orbitalfilled p orbital

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Li

Be

B

C

N

O

F

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Li

Be

B

C

N

O

F

Ne•Ne has a Ne has a

lower IE than lower IE than HeHe

•Both are full,Both are full,

•Ne has more Ne has more shieldingshielding

•Greater Greater distancedistance

Firs

t Ion

izat

ion

ener

gy

Atomic number

H

He

Li

Be

B

C

N

O

F

Ne Na has a lower

IE than Li Both are s1

Na has more shielding

Greater distance

Na

Firs

t Ion

izat

ion

ener

gy

Atomic number

Driving ForcesDriving Forces

•Full Energy LevelsFull Energy Levels require lots require lots of energy to remove their of energy to remove their electrons.electrons.– Noble Gases have full orbitals.Noble Gases have full orbitals.

•Atoms behave in ways to try Atoms behave in ways to try and achieve a noble gas and achieve a noble gas configuration.configuration.

2nd Ionization Energy2nd Ionization Energy

•For elements that reach a filled For elements that reach a filled or half-filled orbital by removing or half-filled orbital by removing 2 electrons, 2nd IE is lower than 2 electrons, 2nd IE is lower than expected.expected.

•True for sTrue for s2 2

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

3rd IE3rd IE

•Using the same logic sUsing the same logic s22pp11

atoms have an low 3rd IE.atoms have an low 3rd IE.

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

•2nd IE and 3rd IE are always 2nd IE and 3rd IE are always higher than 1st IE!!!higher than 1st IE!!!

Trends in Ionic Size: CationsTrends in Ionic Size: Cations

• Cations form by Cations form by losinglosing electrons. electrons.

• Cations are Cations are smallersmaller than the atom they than the atom they came fromcame from – not only do they lose – not only do they lose electrons, they lose an electrons, they lose an entire energy entire energy levellevel..

• Metals form cations.Metals form cations.

• Cations of representative elements have Cations of representative elements have the noble gas configuration the noble gas configuration beforebefore them. them.

Ionic size: AnionsIonic size: Anions•Anions form by Anions form by gaininggaining electrons. electrons.

•Anions are Anions are biggerbigger than the atom than the atom they came fromthey came from – have the same – have the same energy level, but a greater area energy level, but a greater area the nuclear charge needs to coverthe nuclear charge needs to cover

•Nonmetals form anions.Nonmetals form anions.

•Anions of representative elements Anions of representative elements have the noble gas configuration have the noble gas configuration afterafter them. them.

Configuration of IonsConfiguration of Ions

• Ions always have noble gas Ions always have noble gas configurations ( = a full outer level)configurations ( = a full outer level)

•Na atom is: 1sNa atom is: 1s222s2s222p2p663s3s11

•Forms a 1+ sodium ion: 1sForms a 1+ sodium ion: 1s222s2s222p2p66

•Same configuration as neon.Same configuration as neon.

•Metals form ions with the configuration Metals form ions with the configuration of the noble gas of the noble gas beforebefore them - they them - they lose electrons.lose electrons.

Configuration of IonsConfiguration of Ions

•Non-metals form ions by Non-metals form ions by gaining electrons to achieve gaining electrons to achieve noble gas configuration.noble gas configuration.

•They end up with the They end up with the configuration of the noble configuration of the noble gas gas afterafter them. them.

Ion Group trendsIon Group trends

•Each step down a Each step down a group is adding an group is adding an energy levelenergy level

• Ions therefore get Ions therefore get biggerbigger as you go as you go down, because of down, because of the additional the additional energy level.energy level.

Li1+

Na1+

K1+

Rb1+

Cs1+

Ion Period TrendsIon Period Trends•Across the period from left to Across the period from left to right, the nuclear charge right, the nuclear charge increases - so they get increases - so they get smaller.smaller.

•Notice the Notice the energy level changesenergy level changes between anions and cations.between anions and cations.

Li1+

Be2+

B3+

C4+

N3-O2- F1-

Size of Isoelectronic ionsSize of Isoelectronic ions

• Iso- means “the same”Iso- means “the same”

• Isoelectronic ions have the same # Isoelectronic ions have the same # of electronsof electrons

•AlAl3+3+ Mg Mg2+2+ Na Na1+ 1+ Ne FNe F1- 1- OO2- 2- and Nand N3-3- – all have 10 electronsall have 10 electrons

•all have the same configuration: all have the same configuration: 1s1s222s2s222p2p6 6 (which is the noble gas: neon)(which is the noble gas: neon)

Size of Isoelectronic ions?Size of Isoelectronic ions?

• Positive ions that have more protons Positive ions that have more protons would be would be smallersmaller (more protons would (more protons would pull the same # of electrons in closer)pull the same # of electrons in closer)

Al3+

Mg2+

Na1+ Ne F1- O2- N3-

13 12 11 10 9 8 7

#3. Trends in Electronegativity#3. Trends in Electronegativity•Electronegativity is the tendency Electronegativity is the tendency

for an atom to for an atom to attract attract electrons to electrons to itself when it is itself when it is chemically chemically combinedcombined with another element. with another element.

•They share the electron, but how They share the electron, but how equally do they share it?equally do they share it?

•An element with a big An element with a big electronegativity means it pulls electronegativity means it pulls the electron towards itself the electron towards itself strongly!strongly!

Electronegativity Group TrendElectronegativity Group Trend•The further down a The further down a

group, the farther the group, the farther the electron is away from the electron is away from the nucleus, plus the more nucleus, plus the more electrons an atom has.electrons an atom has.

•Thus, more willing to Thus, more willing to share.share.

•Low electronegativity.Low electronegativity.

Electronegativity Period TrendElectronegativity Period Trend

•Metals are at the left of the table.Metals are at the left of the table.

•They let their electrons go easilyThey let their electrons go easily

•Thus, low electronegativityThus, low electronegativity

•At the right end are the nonmetals.At the right end are the nonmetals.

•They want They want moremore electrons. electrons.

•Try to take them away from othersTry to take them away from others

•High electronegativity.High electronegativity.

The arrows indicate the trend: Ionization energy and Electronegativity INCREASE in these directions

Atomic size and Ionic size increase in these directions:

Summary Chart of the trends: Summary Chart of the trends: Figure 6.22, p.178Figure 6.22, p.178

chapter 6 “the periodic table” chemistry. section 6.1 organizing the elements objectives:...

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elements objectives

undiscovered elements

atomic mass arranged

broad classes of elements

periodic table chemistry

law of octaves law of

mendeleevs periodic

similar chemical properties