1 Chapter 7 Periodic Properties of the Elements. 2 The Periodic Table n Developed independently by German Julius Lothar Meyer and Russian Dmitri Mendeleev.

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Chapter 7Chapter 7Periodic Properties of the Periodic Properties of the

ElementsElements

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The Periodic Table The Periodic Table Developed independently by German Developed independently by German

Julius Lothar Meyer and Russian Julius Lothar Meyer and Russian Dmitri Mendeleev (1870’s).Dmitri Mendeleev (1870’s).

Didn’t know much about atom.Didn’t know much about atom. Put in columns by similar properties.Put in columns by similar properties. Predicted properties of missing Predicted properties of missing

elements.elements.

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DetailsDetails Valence electronsValence electrons- the electrons in - the electrons in

the outermost energy levels (not d).the outermost energy levels (not d). Core electronsCore electrons- the inner electrons- the inner electrons

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7.2 Effective Nuclear Charge7.2 Effective Nuclear Charge Properties of atoms depend not only Properties of atoms depend not only

on their electron configurations but on their electron configurations but also on how strongly their outer also on how strongly their outer electrons are attracted to the electrons are attracted to the nucleus.nucleus.

We view the net electric field of the We view the net electric field of the nucleus as if it results from a single nucleus as if it results from a single positive charge. This is known as positive charge. This is known as the EFFECTIVE NUCLEAR CHARGE, the EFFECTIVE NUCLEAR CHARGE, ZZeff.eff.

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ShieldingShielding Valence electrons are attracted to the Valence electrons are attracted to the

nucleus of the atom and are repelled nucleus of the atom and are repelled by the other electrons in the atoms.by the other electrons in the atoms.

– The inner electrons partially shield The inner electrons partially shield or screen the outer electrons from or screen the outer electrons from the attraction of the nucleus.the attraction of the nucleus.

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Periodic Trend of ZPeriodic Trend of Zeffeff The effective nuclear charge The effective nuclear charge

increases as we move across any increases as we move across any row (period) of the table.row (period) of the table.

– The number of core electrons stay The number of core electrons stay the same as we move across the the same as we move across the row, the actual nuclear charge row, the actual nuclear charge increases.increases.

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Periodic Trend of ZPeriodic Trend of Zeffeff Going down a column, the effective Going down a column, the effective

nuclear charge experienced by nuclear charge experienced by valence electrons changes far less valence electrons changes far less than it does across a row.than it does across a row.

– We would expect the effective We would expect the effective nuclear charge for the outer nuclear charge for the outer electrons in lithium and sodium to electrons in lithium and sodium to be about the same, roughly 3-2 = be about the same, roughly 3-2 = +1 for Li and 11-10 = +1 for Na.+1 for Li and 11-10 = +1 for Na.

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7.3 Sizes of Atoms and Ions7.3 Sizes of Atoms and Ions Quantum Mechanical Model – no defined Quantum Mechanical Model – no defined

boundaries at which the electron boundaries at which the electron distribution becomes zero.distribution becomes zero.

We can define atomic size based on the We can define atomic size based on the distance between atoms in various distance between atoms in various situations.situations.– Nonbonding atomic radiusNonbonding atomic radius– Bonding atomic radius (shorter)Bonding atomic radius (shorter)

Allows us to estimate the bond lengths Allows us to estimate the bond lengths between different elements in moleculesbetween different elements in molecules

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PracticePractice Use page 231, Figure 7.5:Use page 231, Figure 7.5:

– Natural gas used in home heating and Natural gas used in home heating and cooking is odorless. Because natural cooking is odorless. Because natural gas leaks pose the danger of explosion gas leaks pose the danger of explosion or suffocation, various smelly or suffocation, various smelly substances are added to the gas to substances are added to the gas to allow detection of a leak. One such allow detection of a leak. One such substance is methyl mercaptan, CHsubstance is methyl mercaptan, CH33SH. SH. Predict the lengths of the C-S , C-H, and Predict the lengths of the C-S , C-H, and S-H bonds in this molecule.S-H bonds in this molecule.

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PracticePractice Use figure 7.5 to predict which will Use figure 7.5 to predict which will

be greater, the P-Br bond length in be greater, the P-Br bond length in PBrPBr33 or the As-Cl bond length in or the As-Cl bond length in AsClAsCl33..

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Periodic Trends in Atomic RadiiPeriodic Trends in Atomic Radii 1. Within each column, atomic radius 1. Within each column, atomic radius

tends to increase from top to bottom.tends to increase from top to bottom.– Results primarily from the increase in Results primarily from the increase in

the principal quantum number of the the principal quantum number of the outer electrons.outer electrons.

2. Within each row, atomic radius tends to 2. Within each row, atomic radius tends to decrease from left to right.decrease from left to right.– The increase in the effective nuclear The increase in the effective nuclear

charge as we move across a row charge as we move across a row steadily draws the valence electrons steadily draws the valence electrons closer to the nucleus.closer to the nucleus.

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You Try It…You Try It… Arrange the following atoms in order Arrange the following atoms in order

of increasing size: of increasing size:

– P, S, As, SeP, S, As, Se Arrange the following atoms in order Arrange the following atoms in order

of increasing atomic radius:of increasing atomic radius:

– Na, Be, MgNa, Be, Mg

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Periodic Trends in Ionic RadiiPeriodic Trends in Ionic Radii 1. Cations are smaller than their 1. Cations are smaller than their

parent atomsparent atoms 2. Anions are larger than their parent 2. Anions are larger than their parent

atoms.atoms. For ions carrying the same charge, For ions carrying the same charge,

size increases as we go down a size increases as we go down a column in the periodic table.column in the periodic table.

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You Try It…You Try It… Arrange these atoms and ions in Arrange these atoms and ions in

order of decreasing size:order of decreasing size:

– MgMg2+2+, Ca, Ca2+2+, Ca, Ca Which of the following atoms and Which of the following atoms and

ions is the largest?ions is the largest?

– SS-2-2, S, O, S, O-2-2

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Isoelectronic seriesIsoelectronic series A group of ions all containing the same number A group of ions all containing the same number

of electronsof electrons– OO-2-2, F, F--, Na, Na++, Mg, Mg2+2+, Al, Al3+3+ all have 10 electrons. all have 10 electrons.

We can list the members in order of increasing We can list the members in order of increasing atomic number, and therefore nuclear charge atomic number, and therefore nuclear charge increases as we move through the series. increases as we move through the series. Because the number of electrons is constant, the Because the number of electrons is constant, the radius of the ion decreases with increasing radius of the ion decreases with increasing nuclear charge, as the electrons are more nuclear charge, as the electrons are more strongly attracted to the nucleus.strongly attracted to the nucleus.– Oxide is the largest ion, smallest atomic Oxide is the largest ion, smallest atomic

numbernumber– aluminum the smallest ion, highest atomic aluminum the smallest ion, highest atomic

numbernumber

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You Try It…You Try It… Arrange the ions of potassium, Arrange the ions of potassium,

chloride, calcium, and sulfide in chloride, calcium, and sulfide in order of decreasing size.order of decreasing size.

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7.4 Ionization Energy7.4 Ionization Energy Ionization energy-the energy required to Ionization energy-the energy required to

remove an electron from a gaseous atomremove an electron from a gaseous atom Highest energy electron removed first. Highest energy electron removed first. First ionization energy (First ionization energy (II11) is that ) is that

required to remove the first electron.required to remove the first electron. Second ionization energy (Second ionization energy (II22) - the ) - the

second electronsecond electron etc. etc.etc. etc.

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Trends in ionization energyTrends in ionization energy for Mg for Mg

• II11 = 735 kJ/mole = 735 kJ/mole• II22 = 1445 kJ/mole = 1445 kJ/mole• II33 = 7730 kJ/mole = 7730 kJ/mole

The effective nuclear charge increases The effective nuclear charge increases as you remove electrons.as you remove electrons.

It takes much more energy to remove a It takes much more energy to remove a core electron than a valence electron core electron than a valence electron because there is less shielding.because there is less shielding.

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Explain this trendExplain this trend For AlFor Al

• II11 = 580 kJ/mole = 580 kJ/mole

• II22 = 1815 kJ/mole = 1815 kJ/mole

• II33 = 2740 kJ/mole = 2740 kJ/mole

• II44 = 11,600 kJ/mole = 11,600 kJ/mole

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Across a PeriodAcross a Period Generally from left to right, Generally from left to right, II11

increases because increases because

– there is a greater nuclear charge there is a greater nuclear charge with the same shielding.with the same shielding.

As you go down a group As you go down a group II11

decreases because electrons are decreases because electrons are farther away.farther away.

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It is not that simpleIt is not that simple ZZeffeff changes as you go across a changes as you go across a

period, so will period, so will II11

Half filled and filled orbitals are Half filled and filled orbitals are harder to remove electrons from.harder to remove electrons from.

here’s what it looks like.here’s what it looks like.

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Periodic Trends in 1Periodic Trends in 1stst Ionization Ionization EnergiesEnergies

1. Within each row, I1 generally increases 1. Within each row, I1 generally increases with increasing atomic number.with increasing atomic number.– Alkali metals show the lowest, noble Alkali metals show the lowest, noble

gases the highest.gases the highest. 2. Within each column, the ionization 2. Within each column, the ionization

energy generally decreases with energy generally decreases with increasing atomic number.increasing atomic number.– He>Ne>Ar>Kr>XeHe>Ne>Ar>Kr>Xe

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You Try It…You Try It… Referring to a periodic table, arrange Referring to a periodic table, arrange

the following atoms in order of the following atoms in order of increasing first ionization energyincreasing first ionization energy

– Ne, Na, P, Ar, KNe, Na, P, Ar, K Write the electron configuration of:Write the electron configuration of:

– Calcium IonCalcium Ion

– Cobalt (III) IonCobalt (III) Ion

– Sulfide IonSulfide Ion

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7.5 Electron Affinities7.5 Electron Affinities The energy change that occurs when The energy change that occurs when

an electron is added to a gaseous an electron is added to a gaseous atomatom

– Affinity = attractionAffinity = attraction Cl(g) Cl(g) Cl Cl++ + e- Delta E = 1251 + e- Delta E = 1251

(first ionization energy) kJ/mol(first ionization energy) kJ/mol Cl(g) + e- Cl(g) + e- Cl Cl-- Delta E = -349 kJ/mol Delta E = -349 kJ/mol

(electron affinity)(electron affinity)

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RememberRemember Ionization energy measures the ease Ionization energy measures the ease

with which an atom LOSES an with which an atom LOSES an electron.electron.

Electron affinity measures the ease Electron affinity measures the ease with which an atom GAINS an with which an atom GAINS an electron.electron.

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Affinity tends to increase across a period Affinity tends to decrease as you go down

• in a period •Electrons farther from the nucleus

•experience less nuclear attraction •Some irregularities due to repulsive

•forces in the relatively small p orbitals

•Electron Affinity - the energy change associated with the addition of an electron

•Values of Electron affinity are always negative, the more negative the value the more stable the atom becomes. Therefore, the more negative the value, the more that atom wants an electron.

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•Table of Electron Affinities

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•A measure of the ability of an atom in a chemical

•compound to attract electrons Electronegativities tend to increase across

• a period Electronegativities tend to decrease down a

• group or remain the same

•Electronegativity

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•Periodic Table of Electronegativities

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Summary of Periodic TrendsSummary of Periodic Trends