The Periodic TableThe Periodic Table

The single most useful The single most useful collection of information in collection of information in

sciencescienceOrOr

Those silly elements Those silly elements are at it again!are at it again!

Chapter 4 Learning ObjectivesChapter 4 Learning Objectives1. Discuss the historical development of the Periodic Table 1. Discuss the historical development of the Periodic Table

including Mendeleev’s contribution and the periodic law.including Mendeleev’s contribution and the periodic law.2. Explain the organization of the modern PT2. Explain the organization of the modern PT3. Discuss the characteristics of the 3 types of elements.3. Discuss the characteristics of the 3 types of elements.4. Describe the characteristic properties of the primary 4. Describe the characteristic properties of the primary

groups of elements.groups of elements.5. Explain the difference in conductivity between metals 5. Explain the difference in conductivity between metals

and non-metals.and non-metals.6. Correlate e- configuration with the arrangement of the 6. Correlate e- configuration with the arrangement of the

PT and properties of the elementsPT and properties of the elements7. Describe periodic trends in atomic radius7. Describe periodic trends in atomic radius8. Describe periodic trends in ionization energy8. Describe periodic trends in ionization energy9. Describe periodic trends in electron affinity9. Describe periodic trends in electron affinity10. Describe periodic trends in melting and boiling points10. Describe periodic trends in melting and boiling points11. Correlate electron shielding to periodic trends11. Correlate electron shielding to periodic trends12. Describe how naturally occurring and synthetic 12. Describe how naturally occurring and synthetic

elements are formed.elements are formed.

The Table past and presentThe Table past and present http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=phttp://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=p

re-1900+Formulationsre-1900+Formulations

These 12 elements were known and used by 1000 These 12 elements were known and used by 1000 BCBC

The ancient Greeks developed the idea The ancient Greeks developed the idea of the four basic “elements”. This of the four basic “elements”. This idea influenced western thought for idea influenced western thought for nearly 2000 yearsnearly 2000 years

Only 1 additional element had been discovered.Only 1 additional element had been discovered.

Alchemy – A great deal of basic chemical knowledge was discovered by alchemists during the 10th to 17th centuries. The knowledge was so interwoven with mysticism and secrecy that little was done with it.

Again, only 1 more element.Again, only 1 more element.

17751775

Antoine Lavoisier Antoine Lavoisier

1789 – The first modern 1789 – The first modern list of elements. Many list of elements. Many accomplishments, accomplishments, including quantitative including quantitative chemistry and law of chemistry and law of conservation of mass.conservation of mass.

(The French revolution failed to recognize (The French revolution failed to recognize his importance)his importance)

28 elements – now we’re getting 28 elements – now we’re getting somewheresomewhere

John Dalton’s list of John Dalton’s list of elements -1808elements -1808

1831 – A 1831 – A classroom table classroom table and blocks to and blocks to learn the learn the elementselements

58 elements!!58 elements!!

““Newland’s Octaves” – John Newland-1864Newland’s Octaves” – John Newland-1864

Every 8Every 8thth element repeats properties!!! One element repeats properties!!! One of the first attempts at a periodic table. of the first attempts at a periodic table. Noble gases had not been discovered!Noble gases had not been discovered!

Dmitri Mendeleev -1871 – Considered Dmitri Mendeleev -1871 – Considered to be the “father of the PT”. to be the “father of the PT”. Arranged elements by atomic mass Arranged elements by atomic mass and properties. and properties.

Mendeleev predicted the properties of Mendeleev predicted the properties of undiscovered elements using his undiscovered elements using his table.table.

The accuracy of his predictions led to The accuracy of his predictions led to the general acceptance of the table.the general acceptance of the table.

Mendeleev did not Mendeleev did not believe the atomic believe the atomic model of the time.model of the time.

Julius Meyer Julius Meyer developed a PT developed a PT around the same around the same time time (Both worked for (Both worked for Bunsen!!)Bunsen!!)

Only a few missing!!Only a few missing!!

Moseley’s Moseley’s (remember him?)(remember him?) discovery of discovery of atomic number led to the…..atomic number led to the…..

Periodic Law – Periodic Law – When arranged by When arranged by atomic number, the chemical and atomic number, the chemical and physical properties of the elements physical properties of the elements will repeat in a regular pattern.will repeat in a regular pattern.

19321932

Notice that the arrangement is still Notice that the arrangement is still different. It was not until the discovery different. It was not until the discovery of electron configuration that the table of electron configuration that the table fit together in its modern form. (Table fit together in its modern form. (Table below-1934)below-1934)

Glenn Seaborg 1945. The discovery of Glenn Seaborg 1945. The discovery of new elements led to the actinide new elements led to the actinide series and our modern PT.series and our modern PT.

The arrangement of the PT:The arrangement of the PT:

There are There are three types of elementsthree types of elements on the on the table.table.

MetalsMetals Semi-ConductorsSemi-Conductors Non-metalsNon-metals

Conduct heat Conduct heat and electricityand electricity

Variable Variable conductanceconductance

Not Not conductive conductive (insulators)(insulators)

Malleable and Malleable and ductileductile

Usually brittleUsually brittle Can be solid, Can be solid, liquid or gasliquid or gas

Metallic lusterMetallic luster Various colorsVarious colors Various colors Various colors or colorlessor colorless

Lose eLose e-- form + form + ionsions

Usually lose eUsually lose e-- Gain eGain e-- form - form -ionsions

Fill in the areas for metals, non-metals, semi-conductors

Label: Groups, periods, alkali metals, alkaline Label: Groups, periods, alkali metals, alkaline earth metals, transition metals, noble gases, earth metals, transition metals, noble gases,

halogens, lanthanides, actinideshalogens, lanthanides, actinides

GroupsGroups – vertical columns on the table. – vertical columns on the table. Elements have the same valence eElements have the same valence e-- configuration and similar properties.configuration and similar properties.

PeriodsPeriods – horizontal rows on the table. – horizontal rows on the table. Properties change as eProperties change as e-- configuration changes. configuration changes.

Alkali metalsAlkali metals – Group 1 – very reactive elements – Group 1 – very reactive elements Alkali earth metalsAlkali earth metals – Group 2 - quite reactive – Group 2 - quite reactive Transition metalsTransition metals – Groups 3-12 (and – Groups 3-12 (and

lanthanides and actinides) – typical metallic lanthanides and actinides) – typical metallic properties.properties.

HalogensHalogens – Group 17 – very reactive non-metals – Group 17 – very reactive non-metals Noble gasesNoble gases – Group 18 – non-reactive – Group 18 – non-reactive

The basis of conductivity:The basis of conductivity:

Electricity is the movement of electrons Electricity is the movement of electrons through a material. The more easily the ethrough a material. The more easily the e-- move, the greater the conductivity.move, the greater the conductivity.

The highest energy eThe highest energy e-- in metals (valence e in metals (valence e-) -)

havehave enough energyenough energy to transfer from atom to transfer from atom to atom. This energy level where eto atom. This energy level where e-- transfer transfer is called the is called the conduction band. conduction band.

It can be thought of as an overlap of the It can be thought of as an overlap of the valence level of the atomsvalence level of the atoms

Picture of metal atoms in a crystal Picture of metal atoms in a crystal structure.structure.

For conductors, there is no energy gap between where For conductors, there is no energy gap between where the ethe e-- resides and the conduction band. resides and the conduction band.

For semi-conductors, the gap is small so little energy is For semi-conductors, the gap is small so little energy is needed to bump electrons into the conduction band.needed to bump electrons into the conduction band.

For insulators, there is a wide gap, so much energy is For insulators, there is a wide gap, so much energy is needed.needed.

Trends in the PTTrends in the PT

Periodic trends – Trend in the properties of Periodic trends – Trend in the properties of elements that vary regularly across and elements that vary regularly across and down the periodic table.down the periodic table.

That’s why they call it the That’s why they call it the periodic periodic table.table. The chemical properties of the elements The chemical properties of the elements

are primarily due to the arrangement of are primarily due to the arrangement of electrons in the atom.electrons in the atom.

The trends in properties on the periodic The trends in properties on the periodic table can be related to how tightly bound table can be related to how tightly bound the valence ethe valence e-- are to the nucleus. are to the nucleus.

The binding force is an electrostatic The binding force is an electrostatic attraction, that is, the force of attraction attraction, that is, the force of attraction between two charges of opposite sign.between two charges of opposite sign.

The amount of force increases with the The amount of force increases with the amount of charge. amount of charge.

2 + charges will attract an e2 + charges will attract an e-- with with greater greater force than 1 + charge, 3 + force than 1 + charge, 3 + charges will be charges will be greater than 2 and so greater than 2 and so on.on.

The amount of force decreases with The amount of force decreases with distance. The further an edistance. The further an e-- is from the is from the nucleus, the less force it will experience.nucleus, the less force it will experience.

Which would you expect to feel more Which would you expect to feel more attraction to the nucleus, an eattraction to the nucleus, an e-- in the 2 in the 2ndnd energy level or one in the 3energy level or one in the 3rdrd energy energy level?level?

Which would you expect to have a greater Which would you expect to have a greater attraction for an eattraction for an e-- , a nucleus with 3 p , a nucleus with 3 p++ or one with 4 por one with 4 p++ ? ?

Trend #1 - Trend #1 - Atomic radiusAtomic radius - The size - The size of an atom. Essentially how far the of an atom. Essentially how far the valence energy level is from the valence energy level is from the nucleus.nucleus.

Note that the radius of the atoms tend to Note that the radius of the atoms tend to increase going down a group. This is increase going down a group. This is expected since we are adding energy expected since we are adding energy levels to the atoms and these levels must levels to the atoms and these levels must be further and further from the nucleus.be further and further from the nucleus.

But wait!!! The radius decreases as we go But wait!!! The radius decreases as we go left to right across a period, even though left to right across a period, even though we are adding more pwe are adding more p++ and e and e--..

Can you think of an explanation for this??Can you think of an explanation for this??

The answer is electron shielding!!!The answer is electron shielding!!!

The radius of an atom is determined by the The radius of an atom is determined by the distance of the valence edistance of the valence e--’s from the ’s from the nucleus.nucleus.

If the valence eIf the valence e--’s feel more positive ’s feel more positive charge, they are pulled in more tightly and charge, they are pulled in more tightly and the radius decreases.the radius decreases.

Inner eInner e--’s (kernel) block out or cancel ’s (kernel) block out or cancel exactly 1 positive charge each (exactly 1 positive charge each (they “shield” they “shield” the outer ethe outer e--’s )’s )

Valence eValence e--’s do not cancel 1 entire + ’s do not cancel 1 entire + charge. They shield less effectively than charge. They shield less effectively than kernel ekernel e--’s.’s.

As we move across a period we add 1 pAs we move across a period we add 1 p++ and 1 eand 1 e-- for each successive element – for each successive element – butbut – we are adding valence e – we are adding valence e--’s – not ’s – not kernel ekernel e--’s. Therefore the effectiveness of ’s. Therefore the effectiveness of the shielding decreases, the valence ethe shielding decreases, the valence e--’s ’s feel more + charge and are pulled in feel more + charge and are pulled in tighter.tighter.

P – 15 p+ 15 e-

5 valence

Si- 14 p+ P- 15 p+ S - 16 p+

14 e- 15 e- 16 e-

4 valence 5 valence 6 valence

10 kernel 10 kernel 10 kernel

Trend #2 – Trend #2 – Ionization energy – Ionization energy – The The amount of energy required to remove anamount of energy required to remove an ee-- from the valence energy level.from the valence energy level.

Ionization energy tends to increase going left to right across a period (more difficult to pull an e- off.

Tends to decrease going down a group (easier to pull an e- off)

The more tightly held an e- is to the nucleus, the more difficult to pull it away, the higher the IE.

Trend #3 Trend #3 Electron affinityElectron affinity is the is the amount of energy released when an amount of energy released when an atom gains an electronatom gains an electron

EA tends to increase going left to right EA tends to increase going left to right across a period (wants eacross a period (wants e--’s more)’s more)

Tends to decrease going down a group Tends to decrease going down a group (less of an attraction for e(less of an attraction for e--’s).’s).

Think of how tightly an atom is holding its Think of how tightly an atom is holding its ee--’s. The more tightly held, the more it ’s. The more tightly held, the more it will attract additional ewill attract additional e--’s.’s.

Melting and boiling pointsMelting and boiling points

MP trends are more difficult to follow. The MP trends are more difficult to follow. The MP and BP are related to the strength of MP and BP are related to the strength of attraction between atoms of an attraction between atoms of an element. The stronger the bond- the element. The stronger the bond- the higher the MP or BP. higher the MP or BP.

In general, metals tend to have higher MP In general, metals tend to have higher MP and non-metals are lower. There are and non-metals are lower. There are significant exceptions to this – Hg, Csignificant exceptions to this – Hg, C

Where do elements come from anyway?Where do elements come from anyway?

No new elements can be formed in any chemical No new elements can be formed in any chemical reaction. These reactions just rearrange reaction. These reactions just rearrange existing elements.existing elements.

Three ways to make an element:Three ways to make an element:1.1. Radioactive decay- An unstable nucleus Radioactive decay- An unstable nucleus

decomposes to form a new elementdecomposes to form a new elementAc → e + Th

2.2. Nuclear fission- A heavier element is split into Nuclear fission- A heavier element is split into lighter oneslighter ones

U → Cs + Rb + 2 n0

3.3. Nuclear fusion- Lighter elements join to form a Nuclear fusion- Lighter elements join to form a heavier one. heavier one.

227 89

0 -1

227 90

235 92

143 55

90 37

Current theory indicated that the Big Bang Current theory indicated that the Big Bang produced mostly H with some He and Li.produced mostly H with some He and Li.

The other elements were ( and still are) The other elements were ( and still are) produced by fusion in stars – up to U (92).produced by fusion in stars – up to U (92).

Synthetic elements are those that do not Synthetic elements are those that do not occur in nature (greater than 92). These occur in nature (greater than 92). These are mostly produced by smashing atoms are mostly produced by smashing atoms of heavier elements together in of heavier elements together in cyclotrons or synchrotrons)cyclotrons or synchrotrons)