Periodic Properties of the Elements. The Periodic Table The modern periodic table was developed in...

Periodic Periodic Properties of the Properties of the

ElementsElements

The Periodic TableThe Periodic Table

The modern periodic table was The modern periodic table was developed in 1872 by Dmitri Mendeleev developed in 1872 by Dmitri Mendeleev (1834-1907). A similar table was also (1834-1907). A similar table was also developed independently by Julius Meyer developed independently by Julius Meyer (1830-1895). (1830-1895).

The table groups elements with The table groups elements with similar properties (both physical and similar properties (both physical and chemical) in vertical columns. As a chemical) in vertical columns. As a result, certain properties recur result, certain properties recur periodically.periodically.


Mendeleev left empty spaces in Mendeleev left empty spaces in his table for elements that hadn’t yet his table for elements that hadn’t yet been discovered. Based on the been discovered. Based on the principle of recurring properties, he principle of recurring properties, he was able to predict the density, was able to predict the density, atomic mass, melting or boiling atomic mass, melting or boiling points and formulas of compounds points and formulas of compounds for several “missing” elements.for several “missing” elements.


metal/non-metal line


The periodic table is based on The periodic table is based on observations of chemical and physical observations of chemical and physical behavior of the elements. It was behavior of the elements. It was developed before the discovery of developed before the discovery of subatomic particles or knowledge of subatomic particles or knowledge of the structure of atoms.the structure of atoms.

The basis of the periodic table The basis of the periodic table can be explained by quantum theory can be explained by quantum theory and the electronic structure of atoms.and the electronic structure of atoms.

Quantum NumbersQuantum Numbers

In addition to In addition to nn, the principal , the principal quantum number, there are three quantum number, there are three additional quantum numbers which additional quantum numbers which describe the type of orbital ( describe the type of orbital ( ll ) , the ) , the spatial orientation of the orbital (spatial orientation of the orbital (mmll ) )

, and the spin of the electron (, and the spin of the electron (mms s )) ..

Quantum NumbersQuantum Numbers

The magnetic quantum number The magnetic quantum number ((mmll ) specifies the spatial orientation ) specifies the spatial orientation of the orbital. An example is to of the orbital. An example is to distinguish between the pdistinguish between the pxx, p, pyy or p or pzz orbitals. orbitals.

Electron SpinElectron Spin

Each orbital, regardless of type, can Each orbital, regardless of type, can contain zero, one or two electrons. If contain zero, one or two electrons. If two electrons occupy the same orbital, two electrons occupy the same orbital, they must spin in opposite directions.they must spin in opposite directions.

The spin is quantized, and can be The spin is quantized, and can be expressed using quantum numbers, or expressed using quantum numbers, or simply specifying the spin as up or down simply specifying the spin as up or down or clockwise and counter-clockwise.or clockwise and counter-clockwise.

The Pauli Exclusion The Pauli Exclusion PrinciplePrinciple

Quantum mechanics dictates Quantum mechanics dictates that no two electrons in an atom can that no two electrons in an atom can have the same four quantum have the same four quantum numbers. Another way of stating the numbers. Another way of stating the Pauli Exclusion PrinciplePauli Exclusion Principle is that if is that if electrons occupy the same orbital, electrons occupy the same orbital, they must have opposite spins.they must have opposite spins.

Multi-electron AtomsMulti-electron Atoms

Orbitals of Orbitals of any type can be any type can be empty, or have 1 empty, or have 1 or two electrons. or two electrons.

Experimental Experimental data indicate that data indicate that if two electrons if two electrons are in the same are in the same orbital, they will orbital, they will spin in opposite spin in opposite directions.directions.

Energy LevelsEnergy LevelsIn any atom or ion In any atom or ion with only 1 with only 1 electronelectron, the , the principal quantum principal quantum number, n, number, n, determines the determines the energy of the energy of the electron. For n=2, electron. For n=2, the 2s and 2p the 2s and 2p orbitals all have the orbitals all have the same energy.same energy.

Energy LevelsEnergy Levels

Likewise, Likewise, the 3s, 3p and the 3s, 3p and 3d orbitals are 3d orbitals are all degenerate, all degenerate, with the same with the same energy.energy.


In a multi-electron atom, there In a multi-electron atom, there is interaction between electrons. As is interaction between electrons. As a result of this interaction, the a result of this interaction, the various subshells of a principal various subshells of a principal quantum level will vary in energy.quantum level will vary in energy.


The energy The energy diagram for the diagram for the first three first three quantum levels quantum levels shows the shows the splitting of splitting of energies. energies.


For a given For a given value of n, the value of n, the energies of the energies of the subshells is as subshells is as follows:follows:

ns<np<nd<nfns<np<nd<nf


The subshells The subshells have different have different energies due to energies due to the the penetrating penetrating abilityability for each for each type of orbital.type of orbital.

Electrons in a Electrons in a 2s orbital can get 2s orbital can get nearer to the nearer to the nucleus than those nucleus than those in a 2p orbital. in a 2p orbital.

Energy Energy LevelsLevels

The electrons The electrons in the 3s orbital in the 3s orbital (top diagram) have (top diagram) have higher probability higher probability to be found near to be found near the nucleus, and the nucleus, and thus greater thus greater penetrating ability penetrating ability than those in 3p or than those in 3p or 3d orbitals.3d orbitals.


Electron configurations are a Electron configurations are a way of noting which subshells of an way of noting which subshells of an atom contain electrons. atom contain electrons. Although Although much of the periodic table was much of the periodic table was developed before the concept of developed before the concept of electron configurations, it turns out electron configurations, it turns out that the position of an element on that the position of an element on the periodic table is directly related the periodic table is directly related to its electron configuration.to its electron configuration.

Electron ConfigurationsElectron Configurations

Write the complete electron Write the complete electron configurations for nitrogen and zinc.configurations for nitrogen and zinc.

How many unpaired electrons does How many unpaired electrons does each atom have?each atom have?

What is the short hand notation for What is the short hand notation for each element.each element.

Hund’s RuleHund’s Rule

When electrons occupy When electrons occupy degenerate orbitals, they occupy degenerate orbitals, they occupy separate orbitals with parallel spins.separate orbitals with parallel spins.

This is the lowest energy, or This is the lowest energy, or ground state, configuration.ground state, configuration.


The electron configurations for Cr The electron configurations for Cr and Cu differ from that expected and Cu differ from that expected based on their positions in the based on their positions in the periodic table.periodic table.


Electron configurations also get Electron configurations also get less predictable for the elements less predictable for the elements near the bottom of the periodic near the bottom of the periodic table.table.

With many quantum levels (With many quantum levels (nn) ) occupied, the energy levels overlap and occupied, the energy levels overlap and the lowest energy arrangement becomes the lowest energy arrangement becomes more difficult to predict. more difficult to predict.

Periodic TrendsPeriodic Trends

Many of the properties of atoms Many of the properties of atoms show clear trends in going across a show clear trends in going across a period (from left to right) or down a period (from left to right) or down a group.group.

In going across a period, each In going across a period, each atom gains a proton in the nucleus atom gains a proton in the nucleus as well as a valence electron.as well as a valence electron.


The increase of positive charge The increase of positive charge in the nucleus isn’t completely in the nucleus isn’t completely cancelled out by the addition of the cancelled out by the addition of the electron. electron.

Electrons added to the valence Electrons added to the valence shell don’t shield each other very shell don’t shield each other very much. As a result, in going across a much. As a result, in going across a period, the period, the effective nuclear chargeeffective nuclear charge (Z(Zeffeff) increases.) increases.

Effective Nuclear ChargeEffective Nuclear Charge

The The effective nuclear chargeeffective nuclear charge (Z(Zeffeff) equals the atomic number (Z) ) equals the atomic number (Z) minus the shielding factor (σ).minus the shielding factor (σ).

ZZeffeff= Z-σ= Z-σ


ZZeffeff= Z-σ= Z-σ


Electrons in Electrons in the valence shell the valence shell are partially are partially shielded from shielded from the nucleus by the nucleus by corecore electrons. electrons.


Electrons in Electrons in pp or or dd orbitals don’t orbitals don’t get too close to the get too close to the nucleus, so they are nucleus, so they are less shielding than less shielding than electrons in electrons in ss orbitals. As a result, orbitals. As a result, effective nuclear effective nuclear charge increases charge increases across a period.across a period.


In going down a group or family, a In going down a group or family, a full quantum level of electrons, along full quantum level of electrons, along with an equal number of protons, is with an equal number of protons, is added. added.

As n increases, the valence As n increases, the valence electrons are, on average, farther from electrons are, on average, farther from the nucleus, and experience less nuclear the nucleus, and experience less nuclear pull due to the shielding by the “core” pull due to the shielding by the “core” electrons. As a result, Zelectrons. As a result, Zeffeff decreases decreases slightly going down a group.slightly going down a group.

Trends- Atomic RadiiTrends- Atomic Radii

Atomic radii are obtained in a variety of Atomic radii are obtained in a variety of ways:ways:

1. For metallic elements, the radius is half 1. For metallic elements, the radius is half the internuclear distance in the crystal, the internuclear distance in the crystal, which is obtained from X-ray data.which is obtained from X-ray data.

2. For diatomic molecules, the radius is 2. For diatomic molecules, the radius is half the bond length.half the bond length.

3. For other elements, estimates of the 3. For other elements, estimates of the radii are made.radii are made.

Trends- Atomic RadiiTrends- Atomic Radii

Atomic radii follow trends directly Atomic radii follow trends directly related to the effective nuclear charge. related to the effective nuclear charge. As ZAs Zeffeff increases across a period, the increases across a period, the electrons are pulled closer to the nucleus, electrons are pulled closer to the nucleus, and atomic radii decrease.and atomic radii decrease.

As ZAs Zeffeff decreases down a group, the decreases down a group, the valence electrons experience less nuclear valence electrons experience less nuclear attraction, and the radius increases.attraction, and the radius increases.

Trends- Trends- Atomic Atomic RadiiRadii

Atomic size Atomic size roughly halves roughly halves across a period, across a period, and doubles and doubles going down a going down a group.group.

Electron Configurations Electron Configurations of Ionsof Ions

The atoms of the main group The atoms of the main group elements (groups IA-VIIA) will form elements (groups IA-VIIA) will form ions by losing or gaining electrons. ions by losing or gaining electrons. The resulting ion will have the same The resulting ion will have the same electron configuration as a noble gas electron configuration as a noble gas (group VIIIA). These configurations (group VIIIA). These configurations are usually very stable.are usually very stable.


Atoms or ions with the same electron Atoms or ions with the same electron configuration (or number of electrons) configuration (or number of electrons) are called are called isoelectronicisoelectronic..

For example, NaFor example, Na++, Mg, Mg2+2+, Ne, F, Ne, F--, , and Oand O2-2- are isoelectronic. The size will are isoelectronic. The size will decrease with increasing positive decrease with increasing positive charge. charge.

OO2-2- > F > F-- >Ne> Na >Ne> Na++> Mg> Mg2+2+


When atoms lose electrons, the When atoms lose electrons, the electrons are always removed from the electrons are always removed from the highest quantum level first.highest quantum level first.

For the first row of transition metals, For the first row of transition metals, this means that the electrons in 4s this means that the electrons in 4s subshell are lost before the 3d subshell.subshell are lost before the 3d subshell.

Fe: [Ar]4sFe: [Ar]4s223d3d66 FeFe2+2+: [Ar] 3d: [Ar] 3d6 6 or or [Ar]4s[Ar]4s003d3d66

Common Ionic ChargesCommon Ionic Charges

The charges of ions of elements The charges of ions of elements in groups 1A-7A (the main groups) in groups 1A-7A (the main groups) are usually predictable. are usually predictable.

Group 1A metals form +1 ions, Group 1A metals form +1 ions, group 2A metals form +2 ions, etc.group 2A metals form +2 ions, etc.

The non-metals of group 5A The non-metals of group 5A have a -3 charge, those of group 6A have a -3 charge, those of group 6A have a -2 charge, and the halogens have a -2 charge, and the halogens form ions with a -1 charge.form ions with a -1 charge.

Typical Ionic ChargesTypical Ionic Charges

Trends – Ionic SizeTrends – Ionic Size

Cations are always smaller than Cations are always smaller than the neutral atom. The loss of one or the neutral atom. The loss of one or more electrons significantly more electrons significantly increases Zincreases Zeffeff, resulting in the , resulting in the valence electrons being pulled closer valence electrons being pulled closer to the nucleus.to the nucleus.

Ionic Size - CationsIonic Size - CationsWithin a group, assuming the same Within a group, assuming the same ionic charge, the size of the ion ionic charge, the size of the ion increases going down the group, due increases going down the group, due to more core electrons shielding the to more core electrons shielding the nucleus as n increases.nucleus as n increases.


Across Across period, the period, the cations get cations get more more positive, positive, and as a and as a result, result, considerablconsiderably smaller.y smaller.


Anions are always larger in size Anions are always larger in size than the neutral atom. The addition than the neutral atom. The addition of one or more electrons results in of one or more electrons results in greater electron-electron repulsion, greater electron-electron repulsion, which causes the valence electrons which causes the valence electrons to “spread out” a bit.to “spread out” a bit.

Size of AnionsSize of Anions

Anions are Anions are always larger than always larger than the neutral atom.the neutral atom.

Size of AnionsSize of Anions

Within a group, assuming Within a group, assuming the same ionic charge, the size the same ionic charge, the size of the ion increases going down of the ion increases going down the group, due to more core the group, due to more core electrons shielding the nucleus electrons shielding the nucleus as n increases.as n increases.

Trends – Ionization Trends – Ionization EnergyEnergy

Ionization energyIonization energy is the energy is the energy required to remove an electron from required to remove an electron from a mole of gaseous atoms or ions.a mole of gaseous atoms or ions.

X(X(gg) + energy ) + energy X X++((gg) + e) + e--

Elements can lose more than Elements can lose more than one electron, so there are 1one electron, so there are 1stst, 2, 2ndnd, 3, 3rdrd, , etc., ionization energies.etc., ionization energies.

Ionization EnergyIonization Energy

It It alwaysalways requires energy to requires energy to remove an electron from a neutral remove an electron from a neutral atom.atom.

As more electrons are removed As more electrons are removed and the ion becomes positively and the ion becomes positively charged, it requires increasingly charged, it requires increasingly greater energy to remove electrons.greater energy to remove electrons.


Ionization energy is a measure of Ionization energy is a measure of how tightly the electrons in the how tightly the electrons in the highest occupied orbitals are held by highest occupied orbitals are held by the nucleus. As a result, it is directly the nucleus. As a result, it is directly related to the effective nuclear charge.related to the effective nuclear charge.

Ionization energy increases going Ionization energy increases going across a period, and decreases going across a period, and decreases going down a group.down a group.

Ionization EnergyIonization Energy

Trends – Electron AffinityTrends – Electron Affinity

Electron AffinityElectron Affinity is the energy change is the energy change when an electron is added to a mole of when an electron is added to a mole of gaseous atoms.gaseous atoms.

X(X(gg) + e) + e-- X X--((gg) ∆E = electron affinity) ∆E = electron affinity

A negative value for the electron affinity A negative value for the electron affinity indicates that the process releases energy, indicates that the process releases energy, and that the anion is easily formed.and that the anion is easily formed.


There is less of a predictable There is less of a predictable trend in electron affinities. In going trend in electron affinities. In going across a period (ignoring the noble across a period (ignoring the noble gases), the electron affinity should gases), the electron affinity should become more negative. Although become more negative. Although this is observed, there are many this is observed, there are many inconsistencies.inconsistencies.

Trends- Electron AffinityTrends- Electron Affinity

In going down a group, the In going down a group, the electron affinity should become less electron affinity should become less negative. Although this trend is negative. Although this trend is observed, there is only a slight observed, there is only a slight change in electron affinities within a change in electron affinities within a group. There may also be group. There may also be inconsistencies in the general trend.inconsistencies in the general trend.

Trends- Electron AffinityTrends- Electron Affinity

The electron The electron affinity of fluorine affinity of fluorine is less negative is less negative than expected. than expected. This may be due to This may be due to additional electron-additional electron-electron repulsion electron repulsion when an electron when an electron is added to such a is added to such a small atom.small atom.

Metallic CharacterMetallic Character

Metallic CharacterMetallic Character

Across a period, metallic behavior Across a period, metallic behavior decreases. Non-metals are often crumbly decreases. Non-metals are often crumbly solids, liquids or gases at room temperature. solids, liquids or gases at room temperature.

Metallic Metallic CharacterCharacter

Metallic Metallic behavior increases behavior increases going down a going down a group.group.

Group IA – the Alkali Group IA – the Alkali MetalsMetals

In discussing the chemistry, In discussing the chemistry, preparation and properties of the preparation and properties of the group IA elements, it is important to group IA elements, it is important to remember that hydrogen is remember that hydrogen is notnot a a group IA metal. It’s properties and group IA metal. It’s properties and reactivity would place it within reactivity would place it within group 7A (diatomic non-metals), group 7A (diatomic non-metals), rather than group IA.rather than group IA.

Group 1A MetalsGroup 1A Metals

The group 1A metals are soft shiny The group 1A metals are soft shiny metals with fairly low densities (Li, Na metals with fairly low densities (Li, Na and K are less dense than water) and low and K are less dense than water) and low melting points. Sodium melts at 98melting points. Sodium melts at 98ooC, C, and cesium melts at 29and cesium melts at 29ooC.C.

The softness, low density and low The softness, low density and low melting points are the result of weaker melting points are the result of weaker metallic bonding due to only one valence metallic bonding due to only one valence electron in this group.electron in this group.

Group 1A Metals - Group 1A Metals - ProductionProduction

Due to the high reactivity with Due to the high reactivity with oxygen and water, all of the metals are oxygen and water, all of the metals are found in nature in ionic form (Mfound in nature in ionic form (M1+1+). ).

The pure metal must be produced The pure metal must be produced in an oxygen and water-free in an oxygen and water-free environment. Typically, an electrical environment. Typically, an electrical current is passed through the melted current is passed through the melted chloride salt. The metal and the chloride salt. The metal and the chlorine gas are collected separately.chlorine gas are collected separately.

Reactivity TrendsReactivity Trends

The chemical behavior of the The chemical behavior of the group IA metals illustrates periodic group IA metals illustrates periodic trends. As the valence electron trends. As the valence electron occupies a higher quantum level, it occupies a higher quantum level, it experiences less nuclear attraction, experiences less nuclear attraction, and is more easily removed.and is more easily removed.

Group 1A Metals + WaterGroup 1A Metals + Water

The reaction with water forms The reaction with water forms hydrogen gas and the aqueous metal hydrogen gas and the aqueous metal hydroxide. The reaction is so hydroxide. The reaction is so vigorous, that the hydrogen may vigorous, that the hydrogen may ignite.ignite.

2 M(2 M(ss) + 2 H) + 2 H22O(O(ll) ) H H22((gg) + 2 ) + 2 MOH(MOH(aqaq))

Metallic CharacterMetallic CharacterThe group IA metals react with water to The group IA metals react with water to produce hydrogen and the metal hydroxide.produce hydrogen and the metal hydroxide.

Metallic behavior increases going down a group.

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