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5 Periodic Trends (aka Periodicity): 1) Atomic Radius 2) Ionic Radius 3) Ionization Energy 4) Electron Affinity 5) ElectroNegativity. ibchem.com/IB/ibfiles/ periodicity /per_ppt/pt_trends.ppt. Periodic Law. - PowerPoint PPT Presentation
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5 Periodic Trends(aka Periodicity):1) Atomic Radius2) Ionic Radius3) Ionization Energy4) Electron Affinity5) ElectroNegativity
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Periodic LawWhen elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.
local.ans.org/mi/Teacher_CD/.../Hist_PeriodicTable.ppt
Trends in Atomic Size
First problem: Where do you start measuring from?
The electron cloud doesn’t have a definite edge.
They get around this by measuring more than 1 atom at a time.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Atomic Size
Atomic Radius = half the distance between two nuclei of a diatomic molecule.
}Radius
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Trends in Atomic Size Influenced by three factors:
1. Energy LevelHigher energy level is further
away.2. Charge on nucleusMore charge pulls electrons in
closer. 3. Shielding effect e <-> e repulsion
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Group trends As we go down
a group... each atom has
another energy level,
so the atoms get bigger.
HLi
Na
K
Rb
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Periodic Trends As you go across a period, the radius
gets smaller. Electrons are in same energy level. More nuclear charge. Outermost electrons are closer.
Na Mg Al Si P S Cl Aribchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Atomic RadiiAtomic Radii
Figure 8.9Figure 8.9
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Effective Nuclear Charge, Z*Effective Nuclear Charge, Z* Z* is the nuclear charge experienced by Z* is the nuclear charge experienced by
the outermost electrons.the outermost electrons. Z* increases across a period owing to Z* increases across a period owing to
incomplete shielding by inner electrons.incomplete shielding by inner electrons. Estimate Z* by --> [ Estimate Z* by --> [ Z - (no. inner electrons) Z - (no. inner electrons) ]] Z=Atomic NumberZ=Atomic Number Charge felt by e- in Li:Z* = Z-#Inner e-=3 - 2 = 1Charge felt by e- in Li:Z* = Z-#Inner e-=3 - 2 = 1 Be Be Z* = 4 - 2 = 2Z* = 4 - 2 = 2 B B Z* = 5 - 2 = 3Z* = 5 - 2 = 3 and so on!and so on!
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Shielding The electron in the
outermost energy level experiences more inter-electron repulsion (shielding).
Second electron has same shielding, if it is in the same period
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Ion 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 a Forming a cation.cation.
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Ion 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.F, 71 pm
9e and 9pF-, 133 pm10 e and 9 p
-
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Trends in Ionic Size
Cations form by losing electrons. Cations are smaller that the atom
they come from. Metals form cations.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Ionic size
Anions form by gaining electrons. Anions are bigger that the atom they
come from. Nonmetals form anions.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Group trends Adding energy level Ions get bigger as
you go down.Li1+
Na1+
K1+
Rb1+
Cs1+
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Periodic Trends Across the period, nuclear charge
increases so they get smaller. Energy level changes between
anions and cations.
Li1+
Be2+
B3+
C4+
N3-O2- F1-
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Trends in Ion SizesTrends in Ion Sizes
Figure 8.13Figure 8.13xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Trends in Ionization Energy The amount of energy required to
completely remove an electron from a gaseous atom.
Removing an electron makes a +1 ion.
The energy required to remove the first electron is called the first ionization energy.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Ionization Energy
The second ionization energy is the energy required to remove the second electron(s).
Always greater than first IE. The third IE is the energy required to
remove a third electron, which is greater than 1st or 2nd IE.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Symbol First Second ThirdHHeLiBeBCNO F Ne
1312 2731 520 900 800 1086 1402 1314 1681 2080
5247 7297 1757 2430 2352 2857 3391 3375 3963
11810 14840 3569 4619 4577 5301 6045 6276 ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Symbol First Second ThirdHHeLiBeBCNO F Ne
1312 2731 520 900 800 1086 1402 1314 1681 2080
5247 7297 1757 2430 2352 2857 3391 3375 3963
11810 14840 3569 4619 4577 5301 6045 6276
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Ionization EnergyIonization EnergySee Screen 8.12See Screen 8.12
IE = energy required to remove an electron IE = energy required to remove an electron from an atom in the gas phase.from an atom in the gas phase.
Mg (g) + 738 kJ ---> MgMg (g) + 738 kJ ---> Mg++ (g) + e- (g) + e-
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Mg (g) + 735 kJ ---> MgMg (g) + 735 kJ ---> Mg++ (g) + e- (g) + e-MgMg+ + (g) + 1451 kJ ---> Mg(g) + 1451 kJ ---> Mg2+2+ (g) + e- (g) + e-
MgMg2+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 lower shell. lower shell.
Ionization EnergyIonization EnergySee Screen 8.12See Screen 8.12
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
What determines IE
The greater the nuclear charge, the greater IE.
Greater distance from nucleus decreases IE
Shielding effect
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Group trends As you go down a group, first IE
decreases because... The electron is further away. More shielding.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Periodic trends
All the atoms in the same period have the same energy level.
Same shielding. But, increasing nuclear charge So IE generally increases from left to
right.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Trends in Electron Affinity
The energy change associated with adding an electron to a gaseous atom(s).
Easiest to add to group 7A or 17(Halogens). Gets them to full energy level. Increase from left to right: atoms become
smaller, with greater nuclear charge. Decrease as we go down a group.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Electron AffinityElectron AffinityA few elements A few elements GAINGAIN electrons to form electrons to form
anionsanions..Electron affinity is the energy change Electron affinity is the energy change
when an electron is added:when an electron is added:
A(g) + e- ---> AA(g) + e- ---> A--(g) E.A. = ∆E(g) E.A. = ∆E
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Affinity for electron Affinity for electron increases across a increases across a period (EA becomes period (EA becomes more negative).more negative).
Affinity decreases down Affinity decreases down a group (EA becomes a group (EA becomes less negative).less negative).
Atom EAAtom EAFF -328 kJ-328 kJClCl -349 kJ-349 kJBrBr -325 kJ-325 kJII -295 kJ-295 kJ
Trends in Electron AffinityTrends in Electron Affinity
xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt
Electronegativity
The tendency for an atom to attract electrons to itself when it is chemically combined with another element.
High electronegativity means it pulls the electron toward it.
Atoms with large negative electron affinity have larger electronegativity.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Group Trend
The further down a group, the farther the electron is away, and the more electrons an atom has.
More willing to share. Low electronegativity.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Periodic Trend Metals are at the left of the table. They let their electrons go easily Low electronegativity At the right end are the nonmetals. They want more electrons. Try to take them away from others High electronegativity.
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Ionization energy and ElectroNegativity INCREASE
ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
Atomic size INCREASES, shielding constant
Ionic size increasesibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt
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