Section 5-3:Section 5-3:Electron Configuration and Electron Configuration and

Periodic PropertiesPeriodic Properties

Coach KelsoeCoach Kelsoe

ChemistryChemistry

Pages 150-164Pages 150-164

Section ObjectivesSection Objectives

Define Define atomicatomic and and ionic radiiionic radii, , ionization energyionization energy, , electron affinityelectron affinity, and , and electronegativityelectronegativity..

Compare the periodic trends of atomic radii, Compare the periodic trends of atomic radii, ionization energy, and electronegativity, and state ionization energy, and electronegativity, and state the reasons for these variations.the reasons for these variations.

Define Define valence electronsvalence electrons, and state how many are , and state how many are present in atoms of each main-group element.present in atoms of each main-group element.

Compare the atomic radii, ionization energies, and Compare the atomic radii, ionization energies, and electronegativities of the d-block elements with electronegativities of the d-block elements with those of the main-group elementsthose of the main-group elements

Atomic RadiiAtomic Radii

The best way to define The best way to define the size of an atom of a the size of an atom of a certain element is to use certain element is to use its atomic radius.its atomic radius.

One way to express an One way to express an atom’s radius is to atom’s radius is to measure the distance measure the distance between the nuclei if two between the nuclei if two identical atoms are identical atoms are chemically bonded chemically bonded together.together.

Atomic RadiiAtomic Radii

The The atomic radiusatomic radius is is defined as one-half the defined as one-half the distance between the distance between the nuclei of identical atoms nuclei of identical atoms that are bonded together.that are bonded together.

The atomic radius The atomic radius increases as you go left increases as you go left and down on the periodic and down on the periodic table.table.

TrendsTrends

Trends in ClothesTrends in Clothes

Trends in ShoesTrends in Shoes

Trends in SchoolTrends in School

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Trends in MusicTrends in Music

Trends in PeopleTrends in People

Atomic Radii Period TrendsAtomic Radii Period Trends

Notice on page 151 that there Notice on page 151 that there is a gradual decrease in is a gradual decrease in atomic radii from left to right.atomic radii from left to right.

If the masses increase left to If the masses increase left to right, why doesn’t the radii right, why doesn’t the radii increase as well?increase as well?

The trend to smaller atoms The trend to smaller atoms across a period is caused by across a period is caused by the increasing positive charge the increasing positive charge of the nucleus!of the nucleus!

Atomic Radii Period TrendsAtomic Radii Period Trends

The reason the atom The reason the atom becomes smaller is becomes smaller is because the nucleus is because the nucleus is positively charged and the positively charged and the orbitals are negatively orbitals are negatively charged.charged.

The more of a charge there The more of a charge there is, the stronger the pull will is, the stronger the pull will be.be.

Atomic Radii Group TrendsAtomic Radii Group Trends

In general, the atomic radii of the main-group In general, the atomic radii of the main-group elements increase down a group.elements increase down a group.

There are a few exceptions, like aluminum There are a few exceptions, like aluminum and gallium. The reason is the presence of and gallium. The reason is the presence of the d-block elements that precede gallium.the d-block elements that precede gallium.

Sample ProblemsSample Problems

Of the elements magnesium, chlorine, Of the elements magnesium, chlorine, sodium, and phosphorus, which has the sodium, and phosphorus, which has the largest atomic radius? Explain.largest atomic radius? Explain. Sodium, because they are all in Period 3, and Sodium, because they are all in Period 3, and

atomic radii increase toward left (small Atom #).atomic radii increase toward left (small Atom #). Of the elements calcium, beryllium, barium, Of the elements calcium, beryllium, barium,

and strontium, which has the largest atomic and strontium, which has the largest atomic radius? Explain.radius? Explain. Barium, because they are all found in Group 2, Barium, because they are all found in Group 2,

and atomic radii increase down a group.and atomic radii increase down a group.

Ionization EnergyIonization Energy

An electron can be removed from an atom if An electron can be removed from an atom if enough energy is supplied.enough energy is supplied.

Using A as a symbol for an atom of any Using A as a symbol for an atom of any element, the process can be expressed as element, the process can be expressed as follows:follows:

The AThe A++ represents an ion of element A with a represents an ion of element A with a single positive charge, called a 1+ ion.single positive charge, called a 1+ ion.

Ionization EnergyIonization Energy

An An ionion is an atom or group is an atom or group of bonded atoms that has a of bonded atoms that has a positive or negative charge.positive or negative charge.

Sodium, for example, forms Sodium, for example, forms an Naan Na++ ion. ion.

Any process that results in Any process that results in the formation of an ion is the formation of an ion is called called ionizationionization..

Atoms can only gain or lose Atoms can only gain or lose electrons, not protons.electrons, not protons.

Ionization EnergyIonization Energy

To compare the ease with which atoms of To compare the ease with which atoms of different elements give up electrons, chemists different elements give up electrons, chemists compare ionization energies.compare ionization energies.

Ionization energyIonization energy is the energy required to is the energy required to remove one electron from a neutral atom of remove one electron from a neutral atom of an element (abbreviated as IE).an element (abbreviated as IE).

The energy required to remove one electron The energy required to remove one electron is designated IEis designated IE11, to remove two electrons, , to remove two electrons,

IEIE22, and so forth., and so forth.

Period Trends for Ionization EnergyPeriod Trends for Ionization Energy

In general, ionization energies In general, ionization energies of the main-group elements of the main-group elements increase left-to-right across increase left-to-right across each period.each period.

The reason for the increase The reason for the increase from left-to-right is the same from left-to-right is the same reason for the decrease in reason for the decrease in atomic radii: the higher atomic radii: the higher nuclear charge.nuclear charge.

Group Trends for Ionization EnergyGroup Trends for Ionization Energy

Among the main-group Among the main-group elements, ionization elements, ionization energies generally energies generally decrease down the groups.decrease down the groups.

As a rule, the farther away As a rule, the farther away from the nucleus the from the nucleus the electrons are, the easier electrons are, the easier they are to lose, hence why they are to lose, hence why the energies decrease the energies decrease down the groups.down the groups.

Removing Electrons from Positive Removing Electrons from Positive IonsIons

With enough energy, electrons can be With enough energy, electrons can be removed from positive ions as well as from removed from positive ions as well as from neutral atoms.neutral atoms.

The energies for removal of additional The energies for removal of additional electrons from an atom are known as the electrons from an atom are known as the second ionization energy, third ionization second ionization energy, third ionization energy, and so on.energy, and so on.

It gets harder to lose more electrons It gets harder to lose more electrons because the nuclear force does not change.because the nuclear force does not change.

Removing Electrons from Positive Removing Electrons from Positive IonsIons

It requires a lot of It requires a lot of energy to remove energy to remove electrons from the electrons from the Noble Gases Noble Gases because their because their outermost energy outermost energy levels are full.levels are full.

This is why Noble This is why Noble Gases are generally Gases are generally unreactive.unreactive.

Sample ProblemSample Problem

Consider two main-group elements A and B. Consider two main-group elements A and B. Element A has a first ionization energy of 419 Element A has a first ionization energy of 419 KJ/mol. Element B has a first ionization KJ/mol. Element B has a first ionization energy of 1000 KJ/mol. For each element, energy of 1000 KJ/mol. For each element, decide if it is more likely to be in the decide if it is more likely to be in the ss-block or -block or pp-block. Which element is more likely to form -block. Which element is more likely to form a positive ion?a positive ion? Element A has a low IE, so it will lose electrons Element A has a low IE, so it will lose electrons

easier so it is probably in the easier so it is probably in the ss-block (Positive ion)-block (Positive ion) Element B is less likely to lose electrons, so it is Element B is less likely to lose electrons, so it is

probably in the probably in the pp-block.-block.

Electron AffinityElectron Affinity

Neutral atoms can also Neutral atoms can also acquire electrons.acquire electrons.

The energy change that The energy change that occurs when an electron occurs when an electron is acquired by a neutral is acquired by a neutral atom is called the atom’s atom is called the atom’s electron affinityelectron affinity..

Affinity is like a date or a Affinity is like a date or a kid’s toy…kid’s toy…

Electron AffinityElectron Affinity

Most atoms release energy when they acquire Most atoms release energy when they acquire an electron.an electron.

Then again, some atoms must be forced to Then again, some atoms must be forced to gain an electron by the addition of energy.gain an electron by the addition of energy.

Period Trends for Electron AffinityPeriod Trends for Electron Affinity

Group 17 elements gain Group 17 elements gain electrons most readily.electrons most readily.

The larger the negative The larger the negative value, the more readily it will value, the more readily it will accept electrons.accept electrons.

In general, electron affinities In general, electron affinities become more negative become more negative across each period within the across each period within the pp-block.-block.

There’s an exception There’s an exception between Groups 14-15.between Groups 14-15.

Group Trends for Electron AffinitiesGroup Trends for Electron Affinities

Trends for electron affinities Trends for electron affinities within groups are not as within groups are not as regular as trends for regular as trends for ionization energies.ionization energies.

As a general rule, electrons As a general rule, electrons add with greater difficulty add with greater difficulty down a group.down a group.

This is because of the This is because of the increase in nuclear charge increase in nuclear charge and increase in atomic radii.and increase in atomic radii.

Adding Electrons to Negative IonsAdding Electrons to Negative Ions

It is always more difficult to It is always more difficult to add a second electron to add a second electron to an already negatively an already negatively charged ion.charged ion.

Second IEs are always Second IEs are always positive.positive.

It is so hard to add It is so hard to add electrons past the full electrons past the full energy level state that it energy level state that it never happens.never happens.

Ionic RadiiIonic Radii

A positive ion is called a A positive ion is called a cationcation.. The formation of a cation by the The formation of a cation by the

loss of one or more electrons loss of one or more electrons always leads to a decrease in always leads to a decrease in atomic radius.atomic radius.

This occurs for two reasons:This occurs for two reasons: The smaller electron cloud The smaller electron cloud

because of fewer electrons.because of fewer electrons. An unbalanced positive charge An unbalanced positive charge

pulls the electrons closer.pulls the electrons closer.

Ionic RadiiIonic Radii

A negative ion is called an A negative ion is called an anionanion.. The formation of an anion by the The formation of an anion by the

addition of one or more electrons addition of one or more electrons always leads to an increase in always leads to an increase in atomic radius.atomic radius.

This occurs due to the opposite This occurs due to the opposite reaction of cation formation:reaction of cation formation: Larger electron cloudLarger electron cloud Higher negative charge repellingHigher negative charge repelling

Valence ElectronsValence Electrons

Chemical compounds form Chemical compounds form because electrons are lost, because electrons are lost, gained, or shared between gained, or shared between atoms.atoms.

The electrons that interact The electrons that interact in this manner are those in in this manner are those in the highest energy levels.the highest energy levels.

These are the electrons These are the electrons most subject to the most subject to the influence of nearby atoms influence of nearby atoms or ions.or ions.

Valence ElectronsValence Electrons

The electrons available to The electrons available to be lost, gained, or shared be lost, gained, or shared in the formation of in the formation of chemical compounds are chemical compounds are called called valence electronsvalence electrons..

Valence electrons are Valence electrons are often located in often located in incompletely filled main incompletely filled main energy levels.energy levels.

Valence ElectronsValence Electrons

For the main group elements, the valence For the main group elements, the valence electrons are the electrons in the outermost electrons are the electrons in the outermost ss and and pp sublevels. sublevels.

The inner electrons are in filled energy levels The inner electrons are in filled energy levels and are held too tightly by the nucleus to be and are held too tightly by the nucleus to be involved in compound formation.involved in compound formation.

Group 1 elements have one valence electron.Group 1 elements have one valence electron. Group 2 elements have two.Group 2 elements have two. Groups 13-18 have valence electrons equal to Groups 13-18 have valence electrons equal to

the group number minus 10. (Group 14 = 4)the group number minus 10. (Group 14 = 4)

ElectronegativityElectronegativity

The valence electrons hold The valence electrons hold atoms together in chemical atoms together in chemical compounds.compounds.

Some compounds have a Some compounds have a concentrated negative concentrated negative charge closer to one atom charge closer to one atom than the other, which has an than the other, which has an effect on the chemical effect on the chemical properties of that compound.properties of that compound.

ElectronegativityElectronegativity

ElectronegativityElectronegativity is a is a measure of the ability of measure of the ability of an atom in a chemical an atom in a chemical compound to attract compound to attract electrons.electrons.

Fluorine is the most Fluorine is the most electronegative element, electronegative element, with an electronegativity with an electronegativity value of 4.value of 4.

Trends for ElectronegativityTrends for Electronegativity

Electronegativities tend to increase across Electronegativities tend to increase across each period, but there are exceptions.each period, but there are exceptions.

Alkali and alkali-earth metals are the least Alkali and alkali-earth metals are the least electronegative.electronegative.

Electronegativities tend to either decrease Electronegativities tend to either decrease down a group or remain about the same.down a group or remain about the same.

The combination of period and group trends The combination of period and group trends result in the highest values belonging to the result in the highest values belonging to the elements in the upper right corner of the table.elements in the upper right corner of the table.

Electron Configurations for Cations Electron Configurations for Cations and Anionsand Anions