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Periodic Trends Chapter 7

Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

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Page 1: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Periodic Trends

Chapter 7

Page 2: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Development of Periodic Table

• Elements in the same group generally have similar chemical properties.

• Properties are not identical, however.

Page 3: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Development of Periodic Table

Mendeleev, for instance, predicted the discovery of germanium (which he called eka-silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon.

Page 4: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

What are the electronic Configurations of the “always”

ions?What does Isoelectronic mean?

Page 5: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Electron Configurations of Cations and Anions

Na [Ne]3s1 Na+ [Ne]

Ca [Ar]4s2 Ca2+ [Ar]

Al [Ne]3s23p1 Al3+ [Ne]

Atoms lose electrons so that cation has a noble-gas outer electron configuration.

H 1s1 H- 1s2 or [He]

F 1s22s22p5 F- 1s22s22p6 or [Ne]

O 1s22s22p4 O2- 1s22s22p6 or [Ne]

N 1s22s22p3 N3- 1s22s22p6 or [Ne]

Atoms gain electrons so that anion has a noble-gas outer electron configuration.

Of Representative Elements

8.2

Page 6: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

8.2

ns1

ns2

ns2 n

p1

ns2 n

p2

ns2 n

p3

ns2 n

p4

ns2 n

p5

ns2 n

p6

d1

d5 d10

4f

5f

Ground State Electron Configurations of the Elements

Page 7: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

+1

+2

+3 -1-2-3

Cations and Anions Of Representative Elements

8.2

Page 8: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Na+: [Ne] Al3+: [Ne] F-: 1s22s22p6 or [Ne]

O2-: 1s22s22p6 or [Ne] N3-: 1s22s22p6 or [Ne]

Na+, Al3+, F-, O2-, and N3- are all isoelectronic with Ne

What neutral atom is isoelectronic with H- ?

H-: 1s2 same electron configuration as He

8.2

Page 9: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Atomic Radii Trends

Who is the biggest?

Who is the smallest?

Why?

Page 10: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Atomic Radii

8.3

Page 11: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

8.3

Page 12: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Effective Nuclear Charge

• In a many-electron atom, electrons are both attracted to the nucleus and repelled by other electrons.

• The nuclear charge that an electron experiences depends on both factors.

Page 13: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Effective Nuclear Charge

The effective nuclear charge, Zeff, is found this way:

Zeff = Z − S

where Z is the atomic number and S is a screening constant, usually close to the number of inner electrons.

Page 14: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Effective nuclear charge (Zeff) is the “positive charge” felt by an electron.

Na

Mg

Al

Si

11

12

13

14

10

10

10

10

1

2

3

4

186

160

143

132

ZeffCoreZ Radius

Zeff = Z - 0 < < Z ( = shielding constant)

Zeff Z – number of inner or core electrons

Within a Periodas Zeff increasesradius decreases

8.3

Page 15: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Sizes of Ions• Ionic size depends

upon:– Nuclear charge.

– Number of electrons.

– Orbitals in which electrons reside.

Page 16: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Sizes of Ions• Cations are smaller

than their parent atoms.– The outermost

electron is removed and repulsions are reduced.

Page 17: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Sizes of Ions• Anions are larger

than their parent atoms.– Electrons are added

and repulsions are increased.

Page 18: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Sizes of Ions

• Ions increase in size as you go down a column.– Due to increasing

value of n.

Page 19: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Sizes of Ions

• In an isoelectronic series, ions have the same number of electrons.

• Ionic size decreases with an increasing nuclear charge.

Page 20: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Cation is always smaller than atom from which it is formed.Anion is always larger than atom from which it is formed.

8.3

Page 21: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

8.3

Page 22: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Do Metals lose or gain electrons?

What do we call the energy required to do this process?

Page 23: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Ionization energy is the minimum energy (kJ/mol) required to remove an electron from a gaseous atom in its ground state.

I1 + X (g) X+

(g) + e-

I2 + X+(g) X2+

(g) + e-

I3 + X2+(g) X3+

(g) + e-

I1 first ionization energy

I2 second ionization energy

I3 third ionization energy

8.4

I1 < I2 < I3

Page 24: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Ionization Energy

• It requires more energy to remove each successive electron.

• When all valence electrons have been removed, the ionization energy takes a quantum leap.

Page 25: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

The next slide has patterns.

Find them.

Page 26: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Filled n=1 shell

Filled n=2 shell

Filled n=3 shellFilled n=4 shell

Filled n=5 shell

8.4

Page 27: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Trends in First Ionization Energies

• Generally, as one goes across a row, it gets harder to remove an electron.– As you go from left to

right, Zeff increases.

Page 28: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

General Trend in First Ionization Energies

8.4

Increasing First Ionization Energy

Incr

ea

sing

Firs

t Io

niz

atio

n E

ner

gy

Page 29: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

What implications can we make from these trends?

What is a stable electronic configuration?

Which electron is removed from a transition element first?

Other questions answered?

Page 30: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Trends in First Ionization Energies

• The first occurs between Groups IIA and IIIA.

• Electron removed from p-orbital rather than s-orbital– Electron farther from

nucleus

– Some repulsion by s electrons.

Page 31: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Trends in First Ionization Energies

• The second occurs between Groups VA and VIA.– Electron removed comes

from doubly occupied orbital.

– Repulsion from other electron in orbital helps in its removal.

Page 32: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Electron Configurations of Cations of Transition Metals

8.2

When a cation is formed from an atom, electrons are removed from the highest n orbital! Do not just remove electrons from the “end” of the electronic configuration!

Fe: [Ar]4s23d6

Fe2+: [Ar]4s03d6 so … [Ar]3d6

Fe3+: [Ar]4s03d5 so … [Ar]3d5

Mn: [Ar]4s23d5

Mn2+: [Ar]4s03d5 so … [Ar]3d5

Why is this so?

Page 33: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

What is the energy called for adding an electron to an atom?

What are the trends?

Why?

Page 34: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Electron affinity is the negative of the energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion.

X (g) + e- X-(g)

8.5

F (g) + e- F-(g)

O (g) + e- O-(g)

H = -328 kJ/mol EA = +328 kJ/mol

H = -141 kJ/mol EA = +141 kJ/mol

Page 35: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

8.5

Page 36: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Trends in Electron Affinity

In general, electron affinity becomes more exothermic as you go from left to right across a row.

Page 37: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Trends in Electron Affinity

There are again, however, two discontinuities in this trend.

Page 38: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Trends in Electron Affinity

• The first occurs between Groups IA and IIA.– Added electron must

go in p-orbital, not s-orbital.

– Electron is farther from nucleus and feels repulsion from s-electrons.

Page 39: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Trends in Electron Affinity

• The second occurs between Groups IVA and VA.– Group VA has no empty

orbitals.

– Extra electron must go into occupied orbital, creating repulsion.

Page 40: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Metals versus Nonmetals

• Metals tend to form cations.• Nonmetals tend to form anions.

Page 41: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Metals

Tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.

Page 42: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Metals

• Compounds formed between metals and nonmetals tend to be ionic.

• Metal oxides tend to be basic.

Page 43: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Nonmetals

• Dull, brittle substances that are poor conductors of heat and electricity.

• Tend to gain electrons in reactions with metals to acquire noble gas configuration.

Page 44: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Nonmetals

• Substances containing only nonmetals are molecular compounds.

• Most nonmetal oxides are acidic.

Page 45: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Metalloids

• Have some characteristics of metals, some of nonmetals.

• For instance, silicon looks shiny, but is brittle and fairly poor conductor.

Page 46: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group Trends

Page 47: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Alkali Metals

• Soft, metallic solids.• Name comes from

Arabic word for ashes.

Page 48: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Alkali Metals

• Found only as compounds in nature.• Have low densities and melting points.• Also have low ionization energies.

Page 49: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Alkali Metals

Their reactions with water are famously exothermic.

Page 50: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Alkali Metals• Alkali metals (except Li) react with oxygen to

form peroxides.• K, Rb, and Cs also form super oxides:

K + O2 KO2

• Produce bright colors when placed in flame.

Page 51: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group 1A Elements (ns1, n 2)

M M+1 + 1e-

2M(s) + 2H2O(l) 2MOH(aq) + H2(g)

4M(s) + O2(g) 2M2O(s)

Incr

easi

ng r

eact

ivity

8.6

M(s) + O2(g) MO2 (s) K, Rb, Cs make super oxides

Li and Na make oxides

Page 52: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Alkaline Earth Metals

• Have higher densities and melting points than alkali metals.

• Have low ionization energies, but not as low as alkali metals.

Page 53: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Alkaline Earth Metals

• Be does not react with water, Mg reacts only with steam, but others react readily with water.

• Reactivity tends to increase as go down group.

Page 54: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group 2A Elements (ns2, n 2)

M M+2 + 2e-

Be(s) + 2H2O(l) No Reaction

Incr

easi

ng r

eact

ivity

8.6

Mg(s) + 2H2O(g) Mg(OH)2(aq) + H2(g)

M(s) + 2H2O(l) M(OH)2(aq) + H2(g) M = Ca, Sr, or Ba

Page 55: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group 3A Elements (ns2np1, n 2)

8.6

4Al(s) + 3O2(g) 2Al2O3(s)

2Al(s) + 6H+(aq) 2Al3+

(aq) + 3H2(g)

Page 56: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group 6A

• Oxygen, sulfur, and selenium are nonmetals.• Tellurium is a metalloid.• The radioactive polonium is a metal.

Page 57: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Oxygen• Two allotropes:

– O2

– O3, ozone

• Three anions:– O2−, oxide– O2

2−, peroxide– O2

1−, superoxide

• Tends to take electrons from other elements (oxidation)

Page 58: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Sulfur

• Weaker oxidizing agent than oxygen.

• Most stable allotrope is S8, a ringed molecule.

Page 59: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group VIIA: Halogens

• Prototypical nonmetals• Name comes from the Greek halos and gennao:

“salt formers”

Page 60: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group VIIA: Halogens

• Large, negative electron affinities– Therefore, tend to oxidize other

elements easily

• React directly with metals to form metal halides

• Chlorine added to water supplies to serve as disinfectant

Page 61: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group 7A Elements (ns1np5, n 2)

X + 1e- X-1

X2(g) + H2(g) 2HX(g)

Incr

easi

ng r

eact

ivity

8.6

Page 62: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group VIIIA: Noble Gases

• Astronomical ionization energies• Positive electron affinities

– Therefore, relatively unreactive

• Monatomic gases

Page 63: Periodic Trends Chapter 7. Development of Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical,

Group VIIIA: Noble Gases

• Xe forms three compounds:– XeF2

– XeF4 (at right)

– XeF6

• Kr forms only one stable compound:– KrF2

• The unstable HArF was synthesized in 2000.