4 Periodic Trends: 1) Atomic Radius 2) Ionic Radius 3) Ionization Energy 4) ElectroNegativity

4 Periodic Trends:1) Atomic Radius2) Ionic Radius3) Ionization Energy4) 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.


Atomic Size

Atomic Radius = half the distance between two nuclei of a diatomic molecule.

}Radius


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


Group trends As we go down

a group... each atom has

another energy level,

so the atoms get bigger.

HLi

Na

K

Rb


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 RadiiAtomic RadiiAtomic Radii

Figure 8.9Figure 8.9

xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

Effective Nuclear Charge, Z*Effective Nuclear Charge, Z*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!


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


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 a Forming a cation.cation.Forming a Forming a cation.cation.


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

-


Trends in Ionic Size

Cations form by losing electrons. Cations are smaller that the atom

they come from. Metals form cations.


Ionic size

Anions form by gaining electrons. Anions are bigger that the atom they

come from. Nonmetals form anions.


Group trends Adding energy level Ions get bigger as

you go down.

Li1+

Na1+

K1+

Rb1+

Cs1+


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-


Trends in Ion SizesTrends in Ion SizesTrends in Ion SizesTrends in Ion Sizes

Figure 8.13Figure 8.13


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.


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.


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


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-


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.




What determines IE

The greater the nuclear charge, the greater IE.

Greater distance from nucleus decreases IE

Shielding effect


Group trends As you go down a group, first IE

decreases because... The electron is further away. More shielding.


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.


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.


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.


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.


Ionization energy and ElectroNegativity INCREASE


Atomic size INCREASES, shielding constant

Ionic size increasesibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

Documents

4 Periodic Trends: 1) Atomic Radius 2) Ionic Radius 3) Ionization Energy 4) ElectroNegativity