Chapter 8 Periodic Properties of the Elements

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Transcript Chapter 8 Periodic Properties of the Elements

Chemistry: A Molecular Approach

, 1 st Ed.

Nivaldo Tro

Chapter 8 Periodic Properties of the Elements

Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA 2007, Prentice Hall

Mendeleev

• • • • • • order elements by atomic mass saw a repeating pattern of properties

Periodic Law

– When the elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically put elements with similar properties in the same column used pattern to predict properties of undiscovered elements where atomic mass order did not fit other properties, he re-ordered by other properties  Te & I Tro, Chemistry: A Molecular Approach 2

Periodic Pattern

nm H 2 O a/b

1 H 2 m 7 Li 2 O m/nm

BeO nm B 2 O 3 a/b

a LiH 9 nm CO 2 nm N 2 O 5 nm BeH 2 11 ( BH 3 ) n 12

a CH 4 14

a NH 3 16

O 2 H 2 O nm 19

HF m 23 Na 2 O m MgO m Al 2 O 3

a/b NaH 24 nm/m SiO 2 nm P 4 O 10 nm SO 3 MgH 2 27 (AlH 3 ) 28

a SiH 4 31

a PH 3 32

H 2 S a nm Cl 2 O 7

a 35.5

HCl m = metal, nm = nonmetal, m/nm = metalloid a = acidic oxide, b = basic oxide, a/b = amphoteric oxide Tro, Chemistry: A Molecular Approach 3

Mendeleev's Predictions

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What vs. Why

• • • Mendeleev’s Periodic Law allows us to predict what the properties of an element will be based on its position on the table it doesn’t explain why the pattern exists Quantum Mechanics is a theory that explains why the periodic trends in the properties exist Tro, Chemistry: A Molecular Approach 5

Electron Spin

• • • experiments by Stern and Gerlach showed a beam of silver atoms is split in two by a magnetic field • the experiment reveals that the electrons spin on their axis as they spin, they generate a magnetic field  spinning charged particles generate a magnetic field if there is an even number of electrons, about half the atoms will have a net magnetic field pointing “North” and the other half will have a net magnetic field pointing “South” Tro, Chemistry: A Molecular Approach 6

Electron Spin Experiment

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Spin Quantum Number,

m s

• spin quantum number describes how the electron spins on its axis  clockwise or counterclockwise 

spin up

spin down

• spins must cancel in an orbital 

paired

•

m s

can have values of ±½ Tro, Chemistry: A Molecular Approach 8

• • •

Pauli Exclusion Principle

no two electrons in an atom may have the same set of 4 quantum numbers therefore no orbital may have more than 2 electrons, and they must have with opposite spins knowing the number orbitals in a sublevel allows us to determine the maximum number of electrons in the sublevel 



sublevel has 1 orbital, therefore it can hold 2 electrons sublevel has 3 orbitals, therefore it can hold 6 electrons 



sublevel has 5 orbitals, therefore it can hold 10 electrons sublevel has 7 orbitals, therefore it can hold 14 electrons Tro, Chemistry: A Molecular Approach 9

Allowed Quantum Numbers

Quantum Number

Principal, n Azimuthal, Magnetic, m Spin, m s

l 0, 1, 2, ..., n-1 -

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Values

1, 2, 3, ...

,...,0,...+ -½, +½

l Number of Values

- 2

n + 1 2

Significance

distance from nucleus shape of orbital orientation of orbital direction of electron spin 10

Quantum Numbers of Helium’s Electrons

• • • • helium has two electrons both electrons are in the first energy level both electrons are in the

orbital of the first energy level since they are in the same orbital, they must have opposite spins

l m l m s n

first electron second electron 1 1 Tro, Chemistry: A Molecular Approach 0 0 0 0 +½ -½ 11

Electron Configurations

• the

ground state

of the electron is the lowest energy orbital it can occupy • the distribution of electrons into the various orbitals in an atom in its ground state is called its

electron configuration

• • • the number designates the principal energy level the letter designates the sublevel and type of orbital the superscript designates the number of electrons in that sublevel • He = 1

2 Tro, Chemistry: A Molecular Approach 12

Orbital Diagrams

• we often represent an orbital as a square and the electrons in that orbital as arrows  the direction of the arrow represents the spin of the electron unoccupied orbital Tro, Chemistry: A Molecular Approach orbital with 1 electron orbital with 2 electrons 13

Sublevel Splitting in Multielectron Atoms

• • • the sublevels in each principal energy level of Hydrogen all have the same energy – we call orbitals with the same energy

degenerate

 or other single electron systems for multielectron atoms, the energies of the sublevels are split  caused by electron-electron repulsion the lower the value of the

energy the sublevel has 

(

= 0) <

(

= 1) <

(

quantum number, the less = 2) <

(

= 3) Tro, Chemistry: A Molecular Approach 14

• • • •

Penetrating and Shielding

the radial distribution function shows that the 2

orbital penetrates more deeply into the 1

orbital than does the 2

the weaker penetration of the 2

sublevel means that electrons in the 2 the nucleus

sublevel experience more repulsive force, they are more shielded from the attractive force of the deeper penetration of the 2

electrons means electrons in the 2 effectively

sublevel experience a greater attractive force to the nucleus and are not shielded as the result is that the electrons in the 2

sublevel are lower in energy than the electrons in the 2

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Penetration & Shielding

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7s 6s 5s 4s 3s 2s 1s 6 6p 5f 4f 5p 4d 4p 3p 2p 3d Notice the following: 1. because of penetration, sublevels within an energy level are not degenerate 2. penetration of the 4 th and higher energy levels is so strong that their

sublevel is lower in energy than the

sublevel of the previous energy level 3. the energy difference between levels becomes smaller for higher energy levels

Order of Subshell Filling in Ground State Electron Configurations

start by drawing a diagram putting each energy shell on a row and listing the subshells, (

s, p, d, f

), for that shell in order of energy, (left-to-right) next, draw arrows through the diagonals, looping back to the next diagonal each time 5

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Filling the Orbitals with Electrons

• • • • • energy shells fill from lowest energy to high subshells fill from lowest energy to high 

→

 Aufbau Principle orbitals that are in the same subshell have the same energy no more than 2 electrons per orbital  Pauli Exclusion Principle when filling orbitals that have the same energy, place one electron in each before completing pairs  Hund’s Rule Tro, Chemistry: A Molecular Approach 19

Example 8.1 – Write the Ground State Electron Configuration and Orbital Diagram and of Magnesium.

Determine the atomic number of the element  from the Periodic Table This gives the number of protons and electrons in the atom Mg Z = 12, so Mg has 12 protons and 12 electrons Tro, Chemistry: A Molecular Approach 20

Example 8.1 – Write the Ground State Electron Configuration and Orbital Diagram and of Magnesium.

Draw 9 boxes to represent the first 3 energy levels

and

orbitals a) since there are only 12 electrons, 9 should be plenty 1s 2s Tro, Chemistry: A Molecular Approach 2p 3s 3p 21

Example 8.1 – Write the Ground State Electron Configuration and Orbital Diagram and of Magnesium.

Add one electron to each box in a set, then  pair the electrons before going to the next set until you use all the electrons When pair, put in opposite arrows   1s 2s Tro, Chemistry: A Molecular Approach       2p  3s 3p 22

Example 8.1 – Write the Ground State Electron Configuration and Orbital Diagram and of Magnesium.

Use the diagram to write the electron  configuration Write the number of electrons in each set as a superscript next to the name of the orbital set 1s 2 2s 2 2p 6 3s 2 = [Ne]3s 2       1s 2s Tro, Chemistry: A Molecular Approach 2p 3s 3p 23

Valence Electrons

• • the electrons in all the subshells with the highest principal energy shell are called the

valence electrons

electrons in lower energy shells are called

core electrons

• chemists have observed that one of the most important factors in the way an atom behaves, both chemically and physically, is the number of valence electrons Tro, Chemistry: A Molecular Approach 24

• • • •

Electron Configuration of Atoms in their Ground State

Kr = 36 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6  there are 28 core electrons and 8 valence electrons Rb = 37 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 [Kr]5s 1 for the 5s

= 5,

1 electron in Rb the set of quantum numbers is = 0,

m l

= 0,

m s

= +½ for an electron in the 2p sublevel, the set of quantum numbers is or (+½)

= 2,

= 1,

m l

= -1 or (0,+1), and

m s

= - ½ Tro, Chemistry: A Molecular Approach 25

Electron Configurations

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Electron Configuration & the Periodic Table

• • the Group number corresponds to the number of valence electrons the length of each “block” is the maximum number of electrons the sublevel can hold • the Period number corresponds to the principal energy level of the valence electrons Tro, Chemistry: A Molecular Approach 27

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5 6 7 1 2 3 4 s 1 s 2 d 1 d 2 d 3 d 4 d 5 d 6 d 7 d 8 d 9 d 10 p 1 p 2 p 3 p 4 p 5 s 2 p 6 f 2 f 3 f 4 f 5 f 6 f 7 f 8 f 9 f 10 f 11 f 12 f 13 f 14 f 14 d 1 Tro, Chemistry: A Molecular Approach 29

1 2 3 4 5 6 7

Electron Configuration from the Periodic Table

8A 1A 3A 4A 5A 6A 7A 2A Ne 3

2 P 3

3 P = [Ne]3

2 3

3 P has 5 valence electrons Tro, Chemistry: A Molecular Approach 30

•

Transition Elements

for the

block metals, the principal energy level is one less than valence shell   one less than the Period number sometimes

electron “promoted” to

Zn sublevel Z = 30, Period 4, Group 2B [Ar]4

2 3

10 4s 3d • for the

block metals, the principal energy level is two less than valence shell  two less than the Period number they really belong to  sometimes

electron in configuration Eu Z = 63, Period 6 [Xe]6

2 4

7 6s 4f 31

1 2 3 4 5 6 7

Electron Configuration from the Periodic Table

8A 1A 3A 4A 5A 6A 7A 2A 4

2 3

10 As 4

3 Ar As = [Ar]4

2 3

10 4

3 As has 5 valence electrons Tro, Chemistry: A Molecular Approach 32

Practice – Use the Periodic Table to write the short electron configuration and orbital diagram for each of the following • Na (at. no. 11) • Te (at. no. 52) • Tc (at. no. 43) Tro, Chemistry: A Molecular Approach 33

Practice – Use the Periodic Table to write the short electron configuration and orbital diagram for each of the following • Na (at. no. 11) [Ne]3s 1 3s • Te (at. no. 52) [Kr]5s 2 4d 10 5p 4 5s 4d • Tc (at. no. 43) [Kr]5s 2 4d 5 5p 5s Tro, Chemistry: A Molecular Approach 4d 34

Properties & Electron Configuration

•

elements in the same column have similar chemical and physical properties because they have the same number of valence electrons in the same kinds of orbitals

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Electron Configuration & Element Properties

• • • • the number of valence electrons largely determines the behavior of an element  chemical and some physical since the number of valence electrons follows a Periodic pattern, the properties of the elements should also be periodic quantum mechanical calculations show that 8 valence electrons should result in a very unreactive atom, an atom that is very stable – and the noble gases, that have 8 valence electrons are all very stable and unreactive conversely, elements that have either one more or one less electron should be very reactive – and the halogens are the most reactive nonmetals and alkali metals the most reactive metals  as a group Tro, Chemistry: A Molecular Approach 36

Electron Configuration & Ion Charge

• • we have seen that many metals and nonmetals form one ion, and that the charge on that ion is predictable based on its position on the Periodic Table  Group 1A = +1, Group 2A = +2, Group 7A = -1, Group 6A = -2, etc.

these atoms form ions that will result in an electron configuration that is the same as the nearest noble gas Tro, Chemistry: A Molecular Approach 37

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Electron Configuration of Anions in their Ground State

• • • anions are formed when atoms gain enough electrons to have 8 valence electrons  filling the

and

sublevels of the valence shell the sulfur atom has 6 valence electrons S atom = 1

2 2

6 3

2 3

4 in order to have 8 valence electrons, it must gain 2 more S 2 anion = 1

2 2

6 3

2 3

6 Tro, Chemistry: A Molecular Approach 39

Electron Configuration of Cations in their Ground State

• • • cations are formed when an atom loses all its valence electrons  resulting in a new lower energy level valence shell  however the process is always endothermic the magnesium atom has 2 valence electrons Mg atom = 1

2 2

6 3

2 when it forms a cation, it loses its valence electrons Mg 2+ cation = 1

2 2

6 Tro, Chemistry: A Molecular Approach 40

Trend in Atomic Radius – Main Group

• • • Different methods for measuring the radius of an atom, and they give slightly different trends    van der Waals radius = nonbonding covalent radius = bonding radius atomic radius is an average radius of an atom based on measuring large numbers of elements and compounds Atomic Radius Increases down group  valence shell farther from nucleus  effective nuclear charge fairly close Atomic Radius Decreases across period (left to right)  adding electrons to same valence shell   effective nuclear charge increases valence shell held closer Tro, Chemistry: A Molecular Approach 41

Effective Nuclear Charge

• • • in a multi-electron system, electrons are simultaneously attracted to the nucleus and repelled by each other outer electrons are

shielded

from full strength of nucleus  screening effect

effective nuclear charge

is net positive charge that is attracting a particular electron •

is nuclear charge,

is electrons in lower energy levels  electrons in same energy level contribute to screening, but very little  effective nuclear charge on sublevels trend,

s > p > d > f

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Z effective

= Z - S 42

Screening & Effective Nuclear Charge

Trends in Atomic Radius Transition Metals

• • increase in size down the Group atomic radii of transition metals roughly the same size across the

block  must less difference than across main group elements  valence shell

2 , not the

electrons  effective nuclear charge on the

2 electrons approximately the same Tro, Chemistry: A Molecular Approach 44

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Example 8.5 – Choose the Larger Atom in Each Pair

or F, N is further left 2) C or Ge 3) N or Al 4) Al or Ge ? opposing trends Tro, Chemistry: A Molecular Approach 47

Electron Configuration of

•

Cations in their Ground State

cations form when the atom loses electrons from the valence shell • for transition metals electrons, may be removed from the sublevel closest to the valence shell Al atom = Al +3 ion = Fe atom = Fe +2 ion = Fe +3 ion = Cu atom = Cu +1 ion = 1s 2 2s 2 2p 6 3s 2 3p 1 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 Tro, Chemistry: A Molecular Approach 48

Magnetic Properties of

•

Transition Metal Atoms & Ions

electron configurations that result in unpaired electrons mean that the atom or ion will have a net magnetic field – this is called

paramagnetism

 will be attracted to a magnetic field • electron configurations that result in all paired electrons mean that the atom or ion will have no magnetic field – this is called

diamagnetism

 slightly repelled by a magnetic field • both Zn atoms and Zn 2+ that the two 4

ions are diamagnetic, showing electrons are lost before the 3

 Zn atoms [Ar]4

2 3

10  Zn 2+ ions [Ar]4

0 3

10 Tro, Chemistry: A Molecular Approach 49

Example 8.6 – Write the Electron Configuration and Determine whether the Fe atom and Fe 3+ ion are Paramagnetic or Diamagnetic • • Fe Z = 26 previous noble gas = Ar  18 electrons ion = [Ar]4

s s

0 3

5 • unpaired electrons • paramagnetic Tro, Chemistry: A Molecular Approach 50

Trends in Ionic Radius

• • • • • • Ions in same group have same charge Ion size increases down the group  higher valence shell, larger Cations smaller than neutral atom; Anions bigger than neutral atom Cations smaller than anions  except Rb +1 & Cs +1 bigger or same size as F -1 and O -2 Larger positive charge = smaller cation  for isoelectronic species  isoelectronic = same electron configuration Larger negative charge = larger anion  for isoelectronic series Tro, Chemistry: A Molecular Approach 51

Periodic Pattern - Ionic Radius (Å)

-1 H +1 2A 3A 4A 5A 6A 7A +1 Li

0.68

Be +2

0.31

+3 B

0.23

C -4 +1 +2 Na

0.97

0.66

0.51

K +1

1.33

0.99

+1 Rb

1.47

Sr +2

0.62

+3 Ga +1 +2

1.13

0.81

In +3 +1 +1 Cs

1.69

Ba +2

1.35

0.95

Tl +3 +1 Si Ge

0.71

0.84

Pb -4 -4 +4 +2 +4 +2 N Bi -3

1.71

O -2

1.40

-1 F

1.33

P Sb -3

2.12

-3 As

2.22

-2 S

1.84

-2 Se

1.98

-2 Te

2.21

Cl -1

1.81

-1 Br

1.96

I -1

2.20

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Ionization Energy

• minimum energy needed to remove an electron from an atom  gas state  endothermic process  valence electron easiest to remove  M(g) + IE 1  M 1+ (g) + 1 e  M +1 (g) + IE 2  M 2+ (g) + 1 e  first ionization energy = energy to remove electron from neutral atom; 2nd IE = energy to remove from +1 ion; etc.

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• • • •

General Trends in 1

Ionization Energy

larger the effective nuclear charge on the electron, the more energy it takes to remove it the farther the most probable distance the electron is from the nucleus, the less energy it takes to remove it 1st IE

decreases

down the group  valence electron farther from nucleus 1st IE generally

increases

across the period  effective nuclear charge increases Tro, Chemistry: A Molecular Approach 56

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Example 8.8 – Choose the Atom in Each Pair with the Higher First Ionization Energy

1) Al or S , Al is further left 2) As or Sb , Sb is further down or Si , Si is further down & left 4) O or Cl ? opposing trends Tro, Chemistry: A Molecular Approach 59

Irregularities in the Trend

• Ionization Energy generally increases from left to right across a Period • except from 2A to 3A, 5A to 6A Be B   1s 2s   1s 2s  2p 2p N O   1s 2s   1s 2s   2p  2p    Tro, Chemistry: A Molecular Approach 60

Irregularities in the First Ionization Energy Trends

Be   1s 2s 2p Be +   1s 2s 2p To ionize Be you must break up a full sublevel, cost extra energy B    B +   1s 2s 2p 1s 2s 2p When you ionize B you get a full sublevel, costs less energy Tro, Chemistry: A Molecular Approach 61

Irregularities in the First Ionization Energy Trends

N   1s 2s   2p  N +   1s 2s   2p To ionize N you must break up a half-full sublevel, cost extra energy O   1s 2s   2p  O +   1s 2s   2p  When you ionize O you get a half-full sublevel, costs less energy Tro, Chemistry: A Molecular Approach 62

• •

Trends in Successive Ionization Energies

• removal of each successive electron costs more energy  shrinkage in size due to having more protons than electrons  outer electrons closer to the nucleus, therefore harder to remove regular increase in energy for each successive valence electron large increase in energy when start removing core electrons Tro, Chemistry: A Molecular Approach 63

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• • • •

Trends in Electron Affinity

energy released when an neutral atom gains an electron  gas state  M(g) + 1e  M -1 (g) + EA defined as exothermic (-), but may actually be endothermic (+)  alkali earth metals & noble gases endothermic, WHY?

more energy released (more -); the larger the EA generally increases across period  becomes more negative from left to right  not absolute  lowest EA in period = alkali earth metal or noble gas  highest EA in period = halogen Tro, Chemistry: A Molecular Approach 65

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• • • •

Metallic Character

Metals  malleable & ductile      shiny, lusterous, reflect light conduct heat and electricity most oxides basic and ionic form cations in solution lose electrons in reactions -

oxidized

Nonmetals  brittle in solid state      dull electrical and thermal insulators most oxides are acidic and molecular form anions and polyatomic anions gain electrons in reactions -

reduced

metallic character increases left metallic character increase down Tro, Chemistry: A Molecular Approach 67

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Example 8.9 – Choose the More Metallic Element in Each Pair

or Te, Sn is further left 2) P or Sb, Sb is further down 3) Ge or In, In is further down & left 4) S or Br ? opposing trends Tro, Chemistry: A Molecular Approach 70

• • • • • •

Trends in the Alkali Metals

atomic radius increases down the column ionization energy decreases down the column very low ionization energies  good reducing agents, easy to oxidize    very reactive, not found uncombined in nature react with nonmetals to form salts compounds generally soluble in water  found in seawater electron affinity decreases down the column melting point decreases down the column  all very low MP for metals density increases down the column  except K  in general, the increase in mass is greater than the increase in volume Tro, Chemistry: A Molecular Approach 71

2 Na(s) + 2 H 2 O(

)  2 NaOH(aq) + H 2 (g) Tro, Chemistry: A Molecular Approach 72

• • •

Trends in the Halogens

atomic radius increases down the column ionization energy decreases down the column very high electron affinities  good oxidizing agents, easy to reduce    very reactive, not found uncombined in nature react with metals to form salts compounds generally soluble in water  found in seawater reactivity increases down the column • • • react with hydrogen to form HX, acids melting point and boiling point increases down the column • density increases down the column  in general, the increase in mass is greater than the increase in volume Tro, Chemistry: A Molecular Approach 73

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Example 8.10 – Write a balanced chemical reaction for the following.

• reaction between potassium metal and bromine gas K(

) + Br 2 (

)  K(

) + Br 2 (

)  K + 2 K(

) + Br 2 (

)  Br  2 KBr(

) (ionic compounds are all solids at room temperature) Tro, Chemistry: A Molecular Approach 75

Example 8.10 – Write a balanced chemical reaction for the following.

• reaction between rubidium metal and liquid water Rb(

) + H 2 O(

)  Rb(

) + H 2 O(

)  2 Rb(

) + 2 H 2 O(

)  Rb + (

) + OH  (

) + H 2 (

) 2 Rb + (

) + 2 OH  (

) + H 2 (

) (alkali metal ionic compounds are soluble in water) Tro, Chemistry: A Molecular Approach 76

Example 8.10 – Write a balanced chemical reaction for the following.

• reaction between chlorine gas and solid iodine Cl 2 (

) + I 2 (

)  Cl 2 (

) + I 2 (

)  ICl write the halogen lower in the column first assume 1:1 ratio, though others also exist 2 Cl 2 (

) + I 2 (

)  2 ICl(

) (molecular compounds found in all states at room temperature) Tro, Chemistry: A Molecular Approach 77

• • • • •

Trends in the Noble Gases

atomic radius increases down the column ionization energy decreases down the column  very high IE very unreactive  only found uncombined in nature  used as “inert” atmosphere when reactions with other gases would be undersirable melting point and boiling point increases down the column  all gases at room temperature  very low boiling points density increases down the column  in general, the increase in mass is greater than the increase in volume Tro, Chemistry: A Molecular Approach 78

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