chapter 8 periodic properties of the elements
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 8Periodic
Properties of the Elements
2007, Prentice Hall
Chemistry: A Molecular Approach, 1st Ed.Nivaldo Tro
Roy KennedyMassachusetts Bay Community College
Wellesley Hills, MA
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
Dobereiner’s “triads” (1817)
Determine the Atomic mass of Sr by averaging the masses of Ca and Ba
87.62 amu
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 (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
Li Be B C N O F
Na Mg Al Si P S Cl
K Ca
Tro, Chemistry: A Molecular Approach 7
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 propertiesTe & I
Tro, Chemistry: A Molecular Approach 8
Mendeleev's Predictions
The Periodic Table
• Periodic Law - Both physical and chemical properties of the elements vary periodically with increasing atomic masso Exceptions Te/I, Ar/K, Co/Nio 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
Tro, Chemistry: A Molecular Approach 10
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 11
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 12
Electron Spin Experiment
Energy Shells and Subshellsn = principal quantum no. (overall size)l = angular momentum quantum no. (shape of orbital)ml = magnetic quantum no. (orientation of orbital)
Tro, Chemistry: A Molecular Approach 14
Spin Quantum Number, ms
• spin quantum number describes how the electron spins on its axisclockwise or counterclockwisespin up or spin down
• spins must cancel in an orbitalpaired
• ms can have values of ±½
Orbital diagram for H
Tro, Chemistry: A Molecular Approach 15
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 sublevels sublevel has 1 orbital, therefore it can hold 2 electronsp sublevel has 3 orbitals, therefore it can hold 6 electronsd 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 16
Allowed Quantum NumbersQuantum Number
Values Number of Values
Significance
Principal, n 1, 2, 3, ... - distance from nucleus
Azimuthal, l 0, 1, 2, ..., n-1 n shape of orbital
Magnetic, ml -l,...,0,...+l 2l + 1 orientation of orbital
Spin, ms -½, +½ 2 direction of electron spin
Tro, Chemistry: A Molecular Approach 17
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
n l ml ms
first
electron1 0 0 +½
second
electron1 0 0 -½
Tro, Chemistry: A Molecular Approach 18
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 19
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
orbital with1 electron
unoccupiedorbital
orbital with2 electrons
Tro, Chemistry: A Molecular Approach 20
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 splitcaused by electron-electron repulsion
• the lower the value of the l quantum number, the less energy the sublevel hass (l = 0) < p (l = 1) < d (l = 2) < f (l = 3)
Tro, Chemistry: A Molecular Approach 21
Penetration & Shielding
Consider bringing an e- close to Li+ 1s2
Tro, Chemistry: A Molecular Approach 22
Penetrating and Shielding• 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
2p is shielded
Ene
rgy
1s
7s
2s
2p
3s
3p3d
6s6p
6d
4s
4p4d
4f
5s
5p
5d5f
Notice the following:1. because of penetration, sublevels within
an energy level are not degenerate2. 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
3. the energy difference between levels becomes smaller for higher energy levels
Tro, Chemistry: A Molecular Approach 24
Order of Subshell Fillingin Ground State Electron Configurations
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s
start by drawing a diagramputting each energy shell ona row and listing the subshells, (s, p, d, f), for that shell in order of energy, (left-to-right)
next, draw arrows throughthe diagonals, looping back to the next diagonaleach time
Tro, Chemistry: A Molecular Approach 25
Tro, Chemistry: A Molecular Approach 26
Filling the Orbitals with Electrons
• energy shells fill from lowest energy to high• subshells fill from lowest energy to high
s → p → d → fAufbau Principle
• orbitals that are in the same subshell have the same energy
• no more than 2 electrons per orbitalPauli Exclusion Principle
• when filling orbitals that have the same energy, place one electron in each before completing pairsHund’s Rule
Tro, Chemistry: A Molecular Approach 27
1. 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
Example 8.1 – Write the Ground State Electron Configuration and Orbital Diagram
and of Magnesium.
Tro, Chemistry: A Molecular Approach 28
2. Draw 9 boxes to represent the first 3 energy levels s and p orbitals
a) since there are only 12 electrons, 9 should be plenty
1s 2s 2p 3s 3p
Example 8.1 – Write the Ground State Electron Configuration and Orbital
Diagram and of Magnesium.
Tro, Chemistry: A Molecular Approach 29
3. 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
Example 8.1 – Write the Ground State Electron Configuration and Orbital
Diagram and of Magnesium.
Tro, Chemistry: A Molecular Approach 30
Example 8.1 – Write the Ground State Electron Configuration and Orbital
Diagram and of Magnesium.
4. 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
1s 2s 2p 3s 3p
Tro, Chemistry: A Molecular Approach 31
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 32
Electron Configuration of Atoms in their Ground State
• Kr = 36 electrons1s22s22p63s23p64s23d104p6
there are 28 core electrons and 8 valence electrons
• Rb = 37 electrons1s22s22p63s23p64s23d104p65s1
[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 33
Electron Configurations
Tro, Chemistry: A Molecular Approach 34
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 35
Tro, Chemistry: A Molecular Approach 36
s1
s2
d1 d2 d3 d4 d5 d6 d7 d8 d9 d10
s2p1 p2 p3 p4 p5
p6
f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 f14d1
1234567
Tro, Chemistry: A Molecular Approach 37
Electron Configuration fromthe Periodic Table
P = [Ne]3s23p3
P has 5 valence electrons
3p3
P
Ne1234567
1A
2A 3A 4A 5A 6A 7A
8A
3s2
38
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
4s 3d
ZnZ = 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 tosometimes d electron in configurationEuZ = 63, Period 6[Xe]6s24f 7 6s 4f
Tro, Chemistry: A Molecular Approach 39
Electron Configuration fromthe Periodic Table
As = [Ar]4s23d104p3
As has 5 valence electrons
As
1234567
1A
2A 3A 4A 5A 6A 7A
8A
4s2
Ar3d10
4p3
Tro, Chemistry: A Molecular Approach 40
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 41
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 5p4d
5s 4d
Tro, Chemistry: A Molecular Approach 42
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 43
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 44
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 TableGroup 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 45
Tro, Chemistry: A Molecular Approach 46
Electron Configuration of Anions in their Ground State
• anions are formed when atoms gain enough electrons to have 8 valence electronsfilling the s and p sublevels of the valence shell
• the sulfur atom has 6 valence electronsS atom = 1s22s22p63s23p4
• in order to have 8 valence electrons, it must gain 2 moreS2- anion = 1s22s22p63s23p6
Tro, Chemistry: A Molecular Approach 47
Electron Configuration of Cations in their Ground State
• cations are formed when an atom loses all its valence electronsresulting in a new lower energy level valence shellhowever the process is always endothermic
• the magnesium atom has 2 valence electronsMg atom = 1s22s22p63s2
• when it forms a cation, it loses its valence electronsMg2+ cation = 1s22s22p6
Tro, Chemistry: A Molecular Approach 48
Tro, Chemistry: A Molecular Approach 49
Electron Configuration of Atoms in their Ground State
• Electrons in some elements are “promoted” to form more stable configurations, e.g.
• Cu = 29 electronsExpected: 1s22s22p63s23p64s23d9
Actual: 1s22s22p63s23p64s13d10
• Cr = 24 electronsExpected: 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 50
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 51
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 nucleusscreening effect
• effective nuclear charge is net positive charge that is attracting a particular electron
• Z is nuclear charge, S is electrons in lower energy levelselectrons in same energy level contribute to screening, but
very littleeffective nuclear charge on sublevels trend, s > p > d > f
Zeffective = Z - S
52
Screening & Effective Nuclear Charge
Tro, Chemistry: A Molecular Approach 53
Trends in Atomic RadiusTransition Metals
• increase in size down the Group
• atomic radii of transition metals roughly the same size across the d blockmust less difference than across main group
elementsvalence shell ns2, not the d electronseffective nuclear charge on the ns2 electrons
approximately the same
Tro, Chemistry: A Molecular Approach 54
Tro, Chemistry: A Molecular Approach 55
Tro, Chemistry: A Molecular Approach 56
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 largerGe is further down so largerAl is further down and left so largerOpposing trends
Tro, Chemistry: A Molecular Approach 57
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 58
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 59
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 = Ar18 electrons
4s 3d
• Fe atom = [Ar]4s23d6
• unpaired electrons • paramagnetic
4s 3d
• Fe3+ ion = [Ar]4s03d5
• unpaired electrons • paramagnetic
Tro, Chemistry: A Molecular Approach 60
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 anionsexcept 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
Periodic Pattern - Ionic Radius (Å)
Li
+1
Na
+1
K
+1
Rb
+1
Cs
+1
Be
+2
Mg
+2
Ca
+2
B
Tl
+3+1
In
+3+1
Ga
+3+1
Al
+3
Sn
+4+2
Ge
-4
Si-4
N
-3
Bi
Sb
As
-3
Te
-2
O
-2
P-3
S
-2
Se
-2
Br
-1
-1
F
I
-1
Cl
-1
H
+1-1
2A 3A 4A 5A 6A 7A
Sr
+2
Ba
+2
C-4
Pb
+4+2
0.68
0.97
1.33
1.47
0.31
0.66
0.99
1.13
1.40
1.84
1.98
2.21
1.33
1.81
1.96
2.20
Al
+3
+3
0.23
0.51
0.62
0.81
1A
1.69 1.35
1.71
2.12
2.22
0.71
0.840.95
62
Tro, Chemistry: A Molecular Approach 63
Tro, Chemistry: A Molecular Approach 64
Ionization Energy• minimum energy needed to remove an electron
from an atom gas stateendothermic processvalence electron easiest to removeM(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 65
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 groupvalence electron farther from nucleus
• 1st IE generally increases across the periodeffective nuclear charge increases
Tro, Chemistry: A Molecular Approach 66
67
Tro, Chemistry: A Molecular Approach 68
Example 8.8 – Choose the Atom in Each Pair with the Higher First Ionization Energy
1) Al or S, Al is further left1) Al or S
2) As or Sb, Sb is further down
1) Al or S
2) As or Sb
3) N or Si, Si is further down & left
1) Al or S
2) As or Sb
3) N or Si
4) O or Cl? opposing trends
Tro, Chemistry: A Molecular Approach 69
Irregularities in the Trend• Ionization Energy generally increases from left
to right across a Period
• except from 2A to 3A, 5A to 6A
Be 1s 2s 2p
B 1s 2s 2p
N 1s 2s 2p
O 1s 2s 2p
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 70
Irregularities in the First Ionization Energy Trends
Be 1s 2s 2p
B 1s 2s 2p
Be+ 1s 2s 2p
To ionize Be you must break up a full sublevel, cost extra energy
B+ 1s 2s 2p
When you ionize B you get a full sublevel, costs less energy
Tro, Chemistry: A Molecular Approach 71
Irregularities in the First Ionization Energy Trends
To ionize N you must break up a half-full sublevel, cost extra energy
N+ 1s 2s 2p
O 1s 2s 2p
N 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 72
Trends in Successive Ionization Energies
• removal of each successive electron costs more energyshrinkage in size due to having more
protons than electronsouter 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 73
Tro, Chemistry: A Molecular Approach 74
Trends in Electron Affinity• energy released when an neutral atom gains an electron
gas stateM(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 rightnot absolute lowest EA in period = alkali earth metal or noble gashighest EA in period = halogen
Tro, Chemistry: A Molecular Approach 75
Tro, Chemistry: A Molecular Approach 76
Metallic Character• Metals
malleable & ductileshiny, lusterous, reflect lightconduct heat and electricitymost oxides basic and ionic form cations in solution lose electrons in reactions - oxidized
• Nonmetalsbrittle in solid statedullelectrical and thermal insulatorsmost oxides are acidic and molecular form anions and polyatomic anionsgain electrons in reactions - reduced
• metallic character increases left• metallic character increase down
Tro, Chemistry: A Molecular Approach 77
Tro, Chemistry: A Molecular Approach 78
Tro, Chemistry: A Molecular Approach 79
Example 8.9 – Choose the More Metallic Element in Each Pair
1) Sn or Te
2) P or Sb
3) Ge or In, In is further down & left
1) Sn or Te
2) P or Sb
3) Ge or In
4) S or Br? opposing trends
1) Sn or Te, Sn is further left1) Sn or Te
2) P or Sb, Sb is further down
Tro, Chemistry: A Molecular Approach 80
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 oxidizevery reactive, not found uncombined in nature react with nonmetals to form saltscompounds 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 81
2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g)
Tro, Chemistry: A Molecular Approach 82
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 reducevery reactive, not found uncombined in nature react with metals to form saltscompounds 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 83
Tro, Chemistry: A Molecular Approach 84
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 85
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 86
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 87
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 88
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 89