1 PERIODIC PERIODIC TRENDS TRENDS
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
PERIODIPERIODIC C
TRENDSTRENDS
PERIODIPERIODIC C
TRENDSTRENDS
2
PERIODICITYPERIODICITYPERIODICITYPERIODICITYPeriod Law-
-physical and chemical properties of elements are a
periodic function of their atomic numbers
3General Periodic General Periodic TrendsTrends
• Atomic and ionic size
• Ionization energy
• Electron affinity, electronegativity
4Effective Nuclear Effective Nuclear ChargeCharge
Z*Z*
5
EffectiveEffective Nuclear Charge, Z* Nuclear Charge, Z*
• Atom Z* Experienced by Electrons in Valence Orbitals
• Li +1.28
• Be -------
• B +2.58
• C +3.22
• N +3.85
• O +4.49
• F +5.13
Increase in Increase in Z* across a Z* across a periodperiod
6General Periodic General Periodic TrendsTrends
Higher effective nuclear chargeElectrons held more tightly
Larger orbitals.
Electrons held less
tightly.
7
Periodic Trend in the Reactivity of
Metals
Periodic Trend in the Reactivity of
Metals
LithiumLithium
SodiumSodium
PotassiumPotassium
MOST
2. Reactivity for Metals
As you go down a group for metals the number of energy levels increase.
Because of this, reactivity increases because the atom is more willing to give away its electron (react).
3.Nonmetalic Trends: Gain electrons Nonmetals on right side, form anions
Going right elements are more nonmetallic (better gainers of electrons)
Going UP elements become more nonmetallic (want to gain)
8. Reactivity nonmetals: Gain e The reason Across = fill the energy level
Going UP a group, nonmetals have same valence but fewer total electrons
Flourine is the most reactive nonmetal.
11Atomic Atomic RadiiRadiiAtomic Atomic RadiiRadii
Figure 8.9Figure 8.9
12
Atomic Atomic SizeSize
Atomic Atomic SizeSize
• Size increasesSize increases, down a group. , down a group.
• Because electrons are added into Because electrons are added into additional energy levels, there is less additional energy levels, there is less attraction.attraction.
• Size decreases Size decreases across a period.across a period.
• Because, increased effective nuclear Because, increased effective nuclear charge.charge.
• Size increasesSize increases, down a group. , down a group.
• Because electrons are added into Because electrons are added into additional energy levels, there is less additional energy levels, there is less attraction.attraction.
• Size decreases Size decreases across a period.across a period.
• Because, increased effective nuclear Because, increased effective nuclear charge.charge.
13
Atomic SizeAtomic SizeAtomic SizeAtomic Size
Size Size decreasesdecreases across a period owing across a period owing to increase in Z*. Each added electron to increase in Z*. Each added electron feels a greater and greater + charge.feels a greater and greater + charge.
LargeLarge SmallSmall
14
Trends in Atomic SizeTrends in Atomic SizeSee Figures 8.9 & 8.10See Figures 8.9 & 8.10
0
50
100
150
200
250
0 5 10 15 20 25 30 35 40
Li
Na
K
Kr
He
NeAr
2nd period
3rd period 1st transitionseries
Radius (pm)
Atomic Number
0
50
100
150
200
250
0 5 10 15 20 25 30 35 40
Li
Na
K
Kr
He
NeAr
2nd period
3rd period 1st transitionseries
Radius (pm)
Atomic Number
15
Ion SizesIon SizesIon SizesIon Sizes
• CATIONSCATIONS are are SMALLERSMALLER than the than the atoms from which they come.atoms from which they come.
• The electron/proton attraction has The electron/proton attraction has gone UP and so size gone UP and so size DECREASESDECREASES..
Li,152 pm3e and 3p
Li +, 78 pm2e and 3 p
+Forming Forming a cation.a cation.Forming Forming a cation.a cation.
16
Ion SizesIon SizesIon SizesIon Sizes
• ANIONSANIONS are are LARGERLARGER than the atoms from than the atoms from which they come.which they come.
• The electron/proton attraction has gone DOWN The electron/proton attraction has gone DOWN and so size and so size INCREASESINCREASES..
• Trends in ion sizes are the same as atom sizes. Trends in ion sizes are the same as atom sizes.
Forming Forming an anion.an anion.Forming Forming an anion.an anion.F, 71 pm
9e and 9pF-, 133 pm10 e and 9 p
-
17
Trends in Ion SizesTrends in Ion SizesTrends in Ion SizesTrends in Ion Sizes
Figure 8.13Figure 8.13
18
Ionization EnergyIonization Energy
IE = energy required to remove an electron from an atom in the gas phase.
Mg (g) + 738 kJ ---> Mg+ (g) + e-
19
Mg (g) + 738 kJ ---> MgMg (g) + 738 kJ ---> Mg++ (g) + e- (g) + e-
MgMg+ + (g) + 1451 kJ ---> Mg(g) + 1451 kJ ---> Mg2+2+ (g) + e- (g) + e-
MgMg++ has 12 protons and only 11 has 12 protons and only 11 electrons. Therefore, IE for Mgelectrons. Therefore, IE for Mg++ > Mg. > Mg.
IE = energy required to remove an electron from an atom in the gas phase.
Ionization EnergyIonization Energy
20
11stst IE: Mg (g) + 735 kJ ---> Mg IE: Mg (g) + 735 kJ ---> Mg++ (g) + e- (g) + e-
22ndnd IE: Mg IE: Mg+ + (g) + 1451 kJ ---> Mg(g) + 1451 kJ ---> Mg2+2+ (g) + e- (g) + e-
33rdrd IE: Mg IE: Mg2+2+ (g) + 7733 kJ ---> Mg (g) + 7733 kJ ---> Mg3+3+ (g) + e- (g) + e-
Energy cost is very high to dip into a Energy cost is very high to dip into a shell of lower n (core electrons). shell of lower n (core electrons). This is why ox. no. = Group no.This is why ox. no. = Group no.
Ionization EnergyIonization Energy
21
Trends in Ionization EnergyTrends in Ionization EnergyTrends in Ionization EnergyTrends in Ionization Energy
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 350
500
1000
1500
2000
2500
1st Ionization energy (kJ/mol)
Atomic NumberH Li Na K
HeNe
ArKr
22
Trends in Ionization Trends in Ionization EnergyEnergy
Trends in Ionization Trends in Ionization EnergyEnergy
• IE decreases down a group
• Because size increases.
• IE increases across a period
• Because effective nuclear
charge increases
• IE increases across a period
• Because effective nuclear
charge increases
23
Electron AffinityElectron Affinity
A few elements GAIN electrons to form anions.
Electron affinity is the energy involved when an atom
gains an electron to form an anion.
X(g) + e- ---> X-(g) E.A. = ∆E
24
Trends in Electron AffinityTrends in Electron Affinity
25
• Affinity for electron increases across a period (EA becomes more negative).
• Affinity decreases down a group (EA becomes less negative).
Atom EAAtom EAFF -328 kJ-328 kJClCl -349 kJ-349 kJBrBr -325 kJ-325 kJII -295 kJ-295 kJ
Atom EAAtom EAFF -328 kJ-328 kJClCl -349 kJ-349 kJBrBr -325 kJ-325 kJII -295 kJ-295 kJ
Trends in Electron Trends in Electron AffinityAffinity
26
Electron Affinity of OxygenElectron Affinity of Oxygen
∆E is EXOthermic
because O has an affinity for
an e-.
[He] O atom
EA = - 141 kJ
+ electron
O [He] - ion
27
Electron Affinity of Electron Affinity of NitrogenNitrogen
∆∆E is E is zero zero for Nfor N- -
due to due to electron-electron-electron electron
repulsions.repulsions.EA = 0 kJ
[He] N atom
[He] N- ion
+ electron
28
Electronegativity
• So how is this different from electron affinity?
• Electron Affinity – is rating of how well an atom wants to gain an electron
• Electronegativity – is rating of how well an atom keeps the electron once it is bonded to another atom
29
Electronegativity
30Electron Configurations and the Periodic Trends
31
“Your Best Friend”
• Periodic table
Related Documents
