periodic properties and trends atomic radii size increases going down a group.size increases going...

Periodic Properties and

Trends

Atomic Atomic RadiiRadii

Atomic Atomic RadiiRadii

• Size IncreasesSize Increases going down a group. going down a group. Because electrons are added further from the Because electrons are added further from the

nucleus, there is less attraction. This is due nucleus, there is less attraction. This is due to additional energy levels and the to additional energy levels and the shielding shielding effecteffect. Each additional energy level . Each additional energy level “shields” the electrons from being pulled in “shields” the electrons from being pulled in toward the nucleus.toward the nucleus.

• Size DECREASES Size DECREASES going across a period.going across a period.

• Size IncreasesSize Increases going down a group. going down a group. Because electrons are added further from the Because electrons are added further from the

nucleus, there is less attraction. This is due nucleus, there is less attraction. This is due to additional energy levels and the to additional energy levels and the shielding shielding effecteffect. Each additional energy level . Each additional energy level “shields” the electrons from being pulled in “shields” the electrons from being pulled in toward the nucleus.toward the nucleus.

• Size DECREASES Size DECREASES going across a period.going across a period.

Atomic SizeAtomic SizeAtomic SizeAtomic Size

Size Size decreasesdecreases across a period owing to across a period owing to increase in the positive charge from the increase in the positive charge from the protons. Each added electron feels a protons. Each added electron feels a greater and greater + charge because the greater and greater + charge because the protons are pulling in the same direction, protons are pulling in the same direction,

where the electrons are scatteredwhere the electrons are scattered..

LargeLarge SmallSmall

Which is Bigger?Which is Bigger?

1) Na or K ?

2) Na or Mg ?

3) Al or I ?


1) Na or K ? K

2) Na or Mg ? Na

3) Al or I ? I

Ion SizesIon SizesIon SizesIon Sizes

Li,152 pm3e and 3p

Li+, 60 pm2e and 3 p

+Does the size goDoes the size goup or down when up or down when losing an electron to losing an electron to form a cation?form a cation?

Does the size goDoes the size goup or down when up or down when losing an electron to losing an electron to form a cation?form a cation?


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 gone UPUP and so size 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.


F,64 pm9e and 9p

F- , 136 pm10 e and 9 p

-Does the size go up or Does the size go up or down when gaining an down when gaining an electron to form an anion?electron to form an anion?

Does the size go up or Does the size go up or down when gaining an down when gaining an electron to form an anion?electron to form an anion?


ANIONSANIONS are are LARGERLARGER than the atoms from than the atoms from which they come.which they come.

The electron/proton attraction has gone The electron/proton attraction has gone DOWNDOWN and so size and so size INCREASESINCREASES..

Trends in ion sizes are the same as Trends in ion sizes are the same as atom sizes.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 Ion SizesTrends in Ion SizesTrends in Ion SizesTrends in Ion Sizes

Figure 8.13Figure 8.13


4) Cl or Cl- ?

5) K+ or K ?

6) Ca or Ca+2?

7) I- or Br- ?


4) Cl or Cl- ? ClCl--

5) K+ or K ? KK

6) Ca or Ca+2 ? CaCa

7) I- or Br- ? II--

Mg + Mg + 738 kJ 738 kJ Mg Mg++ + e- + e-

This is called the FIRST This is called the FIRST ionization energy because ionization energy because

we removed only we removed only thethe OUTERMOST electronOUTERMOST electron

MgMg+ + + + 1451 kJ 1451 kJ Mg Mg2+2+ + e- + e-

When the 2When the 2ndnd e- is removed it is called the 2 e- is removed it is called the 2ndnd IE IE..

IE = energy required to remove an IE = energy required to remove an electron from an atom.electron from an atom.

Ionization EnergyIonization EnergyIonization EnergyIonization Energy

Trends in Ionization Trends in Ionization EnergyEnergy


IE increases across a period IE increases across a period because the positive charge because the positive charge increases.increases.

Metals lose electrons more easily Metals lose electrons more easily than nonmetals.than nonmetals.

Nonmetals lose electrons with Nonmetals lose electrons with difficulty (they like to GAIN difficulty (they like to GAIN electrons).electrons).



• IE decreases down a IE decreases down a group group

• Because size increases Because size increases (Shielding Effect)(Shielding Effect)

• Reducing ability generally Reducing ability generally increases down the increases down the periodic table. periodic table.

Which has a higher 1Which has a higher 1stst ionization ionization energy?energy?

8) Mg or Ca ?

9) Al or S ?

10) Cs or Ba ?

Which has a higher 1Which has a higher 1stst ionization ionization energy?energy?

8) Mg or Ca ? Mg

9) Al or S ? S

10) Cs or Ba ? Ba

ElectronegativityElectronegativity is a measure of the ability of an atom is a measure of the ability of an atom

in a molecule to attract electrons to in a molecule to attract electrons to itself.itself.

Concept proposed byConcept proposed byLinus PaulingLinus Pauling1901-19941901-1994

Concept proposed byConcept proposed byLinus PaulingLinus Pauling1901-19941901-1994

Periodic Trends: Periodic Trends: ElectronegativityElectronegativity

• In a group: Atoms with fewer energy levels can attract electrons better (less shielding). So, electronegativity increases UP a group of elements.

• In a period: More protons, while the energy levels are the same, means atoms can better attract electrons. So, electronegativity increases RIGHT in a period of elements.

ElectronegativityElectronegativity

Which is more electronegative?Which is more electronegative?

11) F or Cl ?

12) Na or K ?

13) Sn or I ?

Which is more electronegative?Which is more electronegative?

11) F or Cl ? F

12) Na or K ? Na

13) Sn or I ? I

Summary of the TrendsSummary of the Trends

Ionic Radii decreasesAtomic mass increases

Density increases

Melting/boiling point increases to stair-step line then decreases.

M.P./B.P. decreases

periodic properties and trends atomic radii size increases going down a group.size increases going...

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