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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. Discovery.

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chapter 8 periodic properties of the elements

Chemistry: A Molecular Approach, 1st Ed.Nivaldo Tro

Chapter 8Periodic Properties of the Elements

Roy Kennedy

Massachusetts Bay Community College

Wellesley Hills, MA

2007, Prentice Hall

discovery
Discovery
  • Elements are organized according to their physical and chemical properties in the Periodic Table
  • Historically, several people contributed to this effort in the late 19th century:
    • Dobereiner- “triads”: Ca,Sr,Ba; Li, Na, K (1817)
    • Newlands- similarity between every eighth element (1864)
    • Mendeleev (1870) - Arranged elements according to atomic mass. Similar elements were arranged together in a “group”
question
Question

Dobereiner’s “triads” (1817)

Determine the Atomic mass of Sr by averaging the masses of Ca and Ba

87.62 amu

newlands
Newlands
  • In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element

Law of Octaves

newlands law of octaves
Newlands “Law of Octaves”
  • Newlands (1864) arranged the elements as follows:
  • Did not contain the Noble gases (yet to be discovered)
  • Not valid for elements with Z > 20
  • His table had 7 groups instead of 8
mendeleev
Mendeleev
  • ordered 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

mendeleev s predictions
Mendeleev\'s Predictions

Tro, Chemistry: A Molecular Approach

the periodic table
The Periodic Table
  • Periodic Law - Both physical and chemical properties of the elements vary periodically with increasing atomic mass
    • Exceptions Te/I, Ar/K, Co/Ni
    • Placed Te (M = 127.6) ahead of I (M=126.9) because Te was similar to Se and S, and I was similar to Cl and Br
  • Moseley showed listing elements based on atomic no. resolved these issues
what vs why
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
  • Laws summarize behavior while theories explain them!
  • Quantum Mechanics is a theory that explains why the periodic trends in the properties exist

Tro, Chemistry: A Molecular Approach

electron spin
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

electron spin experiment
Electron Spin Experiment

Tro, Chemistry: A Molecular Approach

energy shells and subshells
Energy Shells and Subshells

n = principal quantum no. (overall size)

l = angular momentum quantum no. (shape of orbital)

ml = magnetic quantum no. (orientation of orbital)

spin quantum number m s
Spin Quantum Number, ms
  • spin quantum number describes how the electron spins on its axis
    • clockwise or counterclockwise
    • spin up or spin down
  • spins must cancel in an orbital
    • paired
  • mscan have values of ±½

Orbital diagram for H

Tro, Chemistry: A Molecular Approach

pauli exclusion principle
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
    • s sublevel has 1 orbital, therefore it can hold 2 electrons
    • p sublevel has 3 orbitals, therefore it can hold 6 electrons
    • d sublevel has 5 orbitals, therefore it can hold 10 electrons
    • f sublevel has 7 orbitals, therefore it can hold 14 electrons

Tro, Chemistry: A Molecular Approach

allowed quantum numbers
Allowed Quantum Numbers

Tro, Chemistry: A Molecular Approach

quantum numbers of helium s electrons
Quantum Numbers of Helium’s Electrons
  • helium has two electrons
  • both electrons are in the first energy level
  • both electrons are in the s orbital of the first energy level
  • since they are in the same orbital, they must have opposite spins

Tro, Chemistry: A Molecular Approach

electron configurations
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 = 1s2

Tro, Chemistry: A Molecular Approach

orbital diagrams

unoccupied

orbital

orbital with

1 electron

orbital with

2 electrons

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

Tro, Chemistry: A Molecular Approach

sublevel splitting in multielectron atoms
Sublevel Splitting in Multielectron Atoms
  • the sublevels in each principal energy level (n = 2…) of Hydrogen all have the same energy (empty in lowest state) – called degenerate
  • for multielectron atoms, the energies of the sublevels are split
    • caused by electron-electron repulsion
  • the lower the value of the l quantum number, the less energy the sublevel has
    • s (l = 0) < p (l = 1) < d (l = 2) < f (l = 3)

Tro, Chemistry: A Molecular Approach

penetration shielding
Penetration & Shielding

Consider bringing an e- close to Li+ 1s2

Tro, Chemistry: A Molecular Approach

penetrating and shielding
Penetrating and Shielding

2p is shielded

  • the radial distribution function shows that the 2s orbital penetrates more deeply into the 1s orbital than does the 2p
  • the weaker penetration of the 2p sublevel means that electrons in the 2p sublevel experience more repulsive force, they are more shielded from the attractive force of the nucleus
  • the deeper penetration of the 2s electrons means electrons in the 2s sublevel experience a greater attractive force to the nucleus and are not shielded as effectively by 1s e-
  • the result is that the electrons in the 2s sublevel are lower in energy than the electrons in the 2p

Tro, Chemistry: A Molecular Approach

slide23

6d

7s

5f

6p

5d

6s

4f

5p

4d

5s

4p

3d

4s

3p

3s

2p

2s

1s

Energy

  • Notice the following:
  • because of penetration, sublevels within an energy level are not degenerate
  • penetration of the 4th and higher energy levels is so strong that their s sublevel is lower in energy than the d sublevel of the previous energy level
  • the energy difference between levels becomes smaller for higher energy levels
order of subshell filling in ground state electron configurations
Order of Subshell Fillingin 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)

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s

next, draw arrows through

the diagonals, looping back

to the next diagonal

each time

Tro, Chemistry: A Molecular Approach

filling the orbitals with electrons
Filling the Orbitals with Electrons
  • energy shells fill from lowest energy to high
  • subshells fill from lowest energy to high
    • s → p → d → f
    • 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

example 8 1 write the ground state electron configuration and orbital diagram and of magnesium
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

example 8 1 write the ground state electron configuration and orbital diagram and of magnesium1

1s

2s

2p

3s

3p

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 sandp orbitals
    • since there are only 12 electrons, 9 should be plenty

Tro, Chemistry: A Molecular Approach

example 8 1 write the ground state electron configuration and orbital diagram and of magnesium2
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

2p

3s

3p

Tro, Chemistry: A Molecular Approach

example 8 1 write the ground state electron configuration and orbital diagram and of magnesium3



1s



2s



2p







3s

3p

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

1s22s22p63s2 = [Ne]3s2

Tro, Chemistry: A Molecular Approach

valence electrons
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

electron configuration of atoms in their ground state
Electron Configuration of Atoms in their Ground State
  • Kr = 36 electrons

1s22s22p63s23p64s23d104p6

    • there are 28 core electrons and 8 valence electrons
  • Rb = 37 electrons

1s22s22p63s23p64s23d104p65s1

[Kr]5s1

  • for the 5s1 electron in Rb the set of quantum numbers is n = 5, l = 0, ml = 0, ms = +½
  • for an electron in the 2p sublevel, the set of quantum numbers is n = 2, l = 1, ml = -1 or (0,+1), and ms = - ½ or (+½)

Tro, Chemistry: A Molecular Approach

electron configurations1
Electron Configurations

Tro, Chemistry: A Molecular Approach

electron configuration the periodic table
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

slide36

s1

s2

p1 p2 p3 p4 p5

p6

s2

1

2

3

4

5

6

7

d1 d2d3 d4 d5 d6 d7 d8 d9 d10

f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 f14d1

Tro, Chemistry: A Molecular Approach

electron configuration from the periodic table
Electron Configuration fromthe Periodic Table

8A

1A

1

2

3

4

5

6

7

3A

4A

5A

6A

7A

2A

Ne

P

3s2

3p3

P = [Ne]3s23p3

P has 5 valence electrons

Tro, Chemistry: A Molecular Approach

transition elements

4s

3d

6s

4f

Transition Elements
  • for the d block metals, the principal energy level of the d orbital being filled is one less than valence shell
    • one less than the Period number
    • sometimes s electron “promoted” to d sublevel

Zn

Z = 30, Period 4, Group 2B

[Ar]4s23d10

  • for the f block metals, the principal energy level is two less than valence shell
    • two less than the Period number they really belong to
    • sometimes d electron in configuration

Eu

Z = 63, Period 6

[Xe]6s24f 7

electron configuration from the periodic table1
Electron Configuration fromthe Periodic Table

8A

1A

1

2

3

4

5

6

7

3A

4A

5A

6A

7A

2A

3d10

Ar

As

4s2

4p3

As = [Ar]4s23d104p3

As has 5 valence electrons

Tro, Chemistry: A Molecular Approach

slide40
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

slide41
Practice – Use the Periodic Table to write the short electron configuration and orbital diagram for each of the following
  • Na (at. no. 11) [Ne]3s1
  • Te (at. no. 52) [Kr]5s24d105p4
  • Tc (at. no. 43) [Kr]5s24d5

3s

5s

5p

4d

5s

4d

Tro, Chemistry: A Molecular Approach

properties electron configuration
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

Tro, Chemistry: A Molecular Approach

electron configuration element properties
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

electron configuration ion charge
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

electron configuration of anions in their ground state
Electron Configuration of Anions in their Ground State
  • anions are formed when atoms gain enough electrons to have 8 valence electrons
    • filling the s and p sublevels of the valence shell
  • the sulfur atom has 6 valence electrons

S atom = 1s22s22p63s23p4

  • in order to have 8 valence electrons, it must gain 2 more

S2- anion = 1s22s22p63s23p6

Tro, Chemistry: A Molecular Approach

electron configuration of cations in their ground state
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 = 1s22s22p63s2

  • when it forms a cation, it loses its valence electrons

Mg2+ cation = 1s22s22p6

Tro, Chemistry: A Molecular Approach

electron configuration of atoms in their ground state1
Electron Configuration of Atoms in their Ground State
  • Electrons in some elements are “promoted” to form more stable configurations, e.g.
  • Cu = 29 electrons

Expected: 1s22s22p63s23p64s23d9

Actual: 1s22s22p63s23p64s13d10

  • Cr = 24 electrons

Expected: 1s22s22p63s23p64s23d4

Actual: 1s22s22p63s23p64s13d5

The usual reason given for this configuration is that the half-filled or completely filled d-orbitals are more stable as compared to those which are not.

Tro, Chemistry: A Molecular Approach

trend in atomic radius main group
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

effective nuclear charge
Effective Nuclear Charge
  • in a multi-electron system, electrons are simultaneously attracted to the nucleus and repelled by each other
  • outer electrons are shieldedfrom full strength of nucleus
    • screening effect
  • effective nuclear charge is net positive charge that is attracting a particular electron
  • Z is nuclear charge, S 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

Zeffective= Z - S

Tro, Chemistry: A Molecular Approach

trends in atomic radius transition metals
Trends in Atomic RadiusTransition Metals
  • increase in size down the Group
  • atomic radii of transition metals roughly the same size across the d block
    • must less difference than across main group elements
    • valence shell ns2, not the d electrons
    • effective nuclear charge on the ns2 electrons approximately the same

Tro, Chemistry: A Molecular Approach

example 8 5 choose the larger atom in each pair
Example 8.5 – Choose the Larger Atom in Each Pair

N or F?

C or Ge?

N or Al?

Al or Ge?

N is further left so larger

Ge is further down so larger

Al is further down and left so larger

Opposing trends

Tro, Chemistry: A Molecular Approach

electron configuration of cations in their ground state1
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 = 1s22s22p63s23p1

Al+3 ion = 1s22s22p6

Fe atom = 1s22s22p63s23p64s23d6

Fe+2 ion = 1s22s22p63s23p63d6

Fe+3 ion = 1s22s22p63s23p63d5

Cu atom = 1s22s22p63s23p64s13d10

Cu+1 ion = 1s22s22p63s23p63d10

Tro, Chemistry: A Molecular Approach

magnetic properties of transition metal atoms ions
Magnetic Properties of Transition Metal Atoms & Ions
  • Ferromagnetism – certain mateirals form permanent magnets
  • electron configurations that result in unpaired electrons mean that in the presence of an externally applied magnetic field 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 an externally applied magnetic field
  • both Zn atoms and Zn2+ ions not magnetic (diamagnetic), showing that the two 4s electrons are lost before the 3d
    • Zn atoms [Ar]4s23d10
    • Zn2+ ions [Ar]4s03d10

Tro, Chemistry: A Molecular Approach

slide59

Fe atom = [Ar]4s23d6

  • unpaired electrons
  • paramagnetic

4s

3d

  • Fe3+ ion = [Ar]4s03d5
  • unpaired electrons
  • paramagnetic

4s

3d

Example 8.6 – Write the Electron Configuration and Determine whether the Fe atom and Fe3+ ion are Paramagnetic or Diamagnetic
  • Fe Z = 26 (elemental iron is magnetic!)
  • previous noble gas = Ar
    • 18 electrons

Tro, Chemistry: A Molecular Approach

trends in ionic radius
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

periodic pattern ionic radius

+1

-1

H

+1

+2

-3

-1

-2

-4

Li

Be

B

C

N

O

F

+2

+3

+3

-2

-1

-4

-3

Na

Mg

Al

Al

Si

P

S

Cl

+1

+2

+3

+1

-4

-3

-2

-1

K

Ca

Ga

Ge

As

Se

Br

+1

+2

+3

+1

+4

+2

-2

-1

Rb

Sr

In

Sn

Sb

Te

I

+1

+2

+3

+1

+4

+2

Cs

Ba

Tl

Pb

Bi

1A

Periodic Pattern - Ionic Radius (Å)

2A 3A 4A 5A 6A 7A

+3

1.71

1.40

1.33

0.68

0.31

0.23

+1

0.51

2.12

1.81

0.66

1.84

0.97

0.62

1.96

1.98

0.99

1.33

2.22

0.81

0.71

2.20

1.13

2.21

1.47

0.84

0.95

1.69

1.35

ionization energy
Ionization Energy
  • minimum energy needed to remove an electron from an atom
    • gas state
    • endothermic process
    • valence electron easiest to remove
    • M(g) + IE1 M+(g) + 1 e-
    • M+(g) + IE2  M2+(g) + 1 e-
      • first ionization energy = energy to remove electron from neutral atom; 2nd IE = energy to remove from +1 ion; etc.

Tro, Chemistry: A Molecular Approach

general trends in 1 st ionization energy
General Trends in 1st 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

example 8 8 choose the atom in each pair with the higher first ionization energy

Al or S, Al is further left

  • Al or S
  • As or Sb, Sb is further down
  • Al or S
  • As or Sb
  • N or Si, Si is further down & left
  • Al or S
  • As or Sb
  • N or Si
  • O or Cl? opposing trends
Example 8.8 – Choose the Atom in Each Pair with the Higher First Ionization Energy

Tro, Chemistry: A Molecular Approach

irregularities in the trend

N

Be

















1s

1s

1s

1s

2s

2s

2s

2s

2p

2p

2p

2p



B

O

Irregularities in the Trend
  • Ionization Energy generally increases from left to right across a Period
  • except from 2A to 3A, 5A to 6A

Which is easier to remove an electron from B or Be? Why?

Which is easier to remove an electron from N or O? Why?

Tro, Chemistry: A Molecular Approach

irregularities in the first ionization energy trends

B

B+

1s

2s

2p

1s

2s

2p















Irregularities in the First Ionization Energy Trends

Be

Be+

1s

2s

2p

1s

2s

2p

To ionize Be you must break up a full sublevel, cost extra energy

When you ionize B you get a full sublevel, costs less energy

Tro, Chemistry: A Molecular Approach

irregularities in the first ionization energy trends1

N

N+

1s

2s

2p

1s

2s

2p



O

O+

1s

2s

2p

1s

2s

2p

















Irregularities in the First Ionization Energy Trends

To ionize N you must break up a half-full sublevel, cost extra energy

When you ionize O you get a half-full sublevel, costs less energy

Tro, Chemistry: A Molecular Approach

trends in successive ionization energies
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

trends in electron affinity
Trends in Electron Affinity
  • energy released when an neutral atom gains an electron
    • gas state
    • M(g) + 1e- M-(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

metallic character
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

example 8 9 choose the more metallic element in each pair

Sn or Te

  • P or Sb
  • Ge or In, In is further down & left
  • Sn or Te
  • P or Sb
  • Ge or In
  • S or Br? opposing trends
  • Sn or Te, Sn is further left
  • Sn or Te
  • P or Sb, Sb is further down
Example 8.9 – Choose the More Metallic Element in Each Pair

Tro, Chemistry: A Molecular Approach

trends in the alkali metals
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

slide81

2 Na(s) + 2 H2O(l)  2 NaOH(aq) + H2(g)

Tro, Chemistry: A Molecular Approach

trends in the halogens
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

example 8 10 write a balanced chemical reaction for the following
Example 8.10 – Write a balanced chemical reaction for the following.
  • reaction between potassium metal and bromine gas

K(s) + Br2(g) 

K(s) + Br2(g)  K+ Br

2 K(s) + Br2(g)  2 KBr(s)

(ionic compounds are all solids at room temperature)

Tro, Chemistry: A Molecular Approach

example 8 10 write a balanced chemical reaction for the following1
Example 8.10 – Write a balanced chemical reaction for the following.
  • reaction between rubidium metal and liquid water

Rb(s) + 2H2O(l) 

Rb(s) + H2O(l)  Rb+(aq) + OH(aq)+ H2(g)

2 Rb(s) + 2 H2O(l)  2 Rb+(aq) + 2 OH(aq)+ H2(g)

(alkali metal ionic compounds are soluble in water)

Tro, Chemistry: A Molecular Approach

example 8 10 write a balanced chemical reaction for the following2
Example 8.10 – Write a balanced chemical reaction for the following.
  • reaction between chlorine gas and solid iodine

Cl2(g) + I2(s) 

Cl2(g) + I2(s)  ICl

write the halogen lower in the column first

assume 1:1 ratio, though others also exist

2 Cl2(g) + I2(s)  2 ICl(g)

(molecular compounds found in all states at room temperature)

Tro, Chemistry: A Molecular Approach

trends in the noble gases
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 undesirable

Tro, Chemistry: A Molecular Approach

trends in the noble gases1
Trends in the Noble Gases
  • 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

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