There are 6 patterns or trends we discuss There are 6 patterns or trends we discuss when looking at the periodic table…when looking at the periodic table…

1.1. ReactivityReactivity

2.2. Atomic radius or sizeAtomic radius or size

3.3. Ionic radiusIonic radius

4.4. Ionization energyIonization energy

5.5. Electron AffinityElectron Affinity

6.6. ElectronegativityElectronegativity

We have already discussed reactivity – let’s We have already discussed reactivity – let’s look at the other five!look at the other five!

Atomic radius or size….Atomic radius or size….

It decreases as It decreases as we go across the we go across the periodic table…periodic table… It increases as It increases as we go down the we go down the periodic table…periodic table… Why….?Why….?

Look at Na and Mg….Look at Na and Mg…. How many full shields are blocking the How many full shields are blocking the nucleus of Na?nucleus of Na?How many full shields are blocking the How many full shields are blocking the nucleus of Mg?nucleus of Mg?Both have 2 full shields blocking the Both have 2 full shields blocking the nucleus….nucleus….Na has how many protons?Na has how many protons?Mg has how many protons?Mg has how many protons?Calculate the effective nuclear charge of Calculate the effective nuclear charge of each atom now…..each atom now…..Na has an effective nuclear charge of +1, Na has an effective nuclear charge of +1, and Mg has an effective nuclear charge of +2and Mg has an effective nuclear charge of +2Mg is twice as effective as pulling in Mg is twice as effective as pulling in electrons through two energy levels as Na, electrons through two energy levels as Na, making it a smaller atom…making it a smaller atom…

SodiumSodium

MagnesiumMagnesium

What is the pattern…?What is the pattern…? As we go across the periodic table, As we go across the periodic table, atoms get smaller…atoms get smaller… But how can this be? You are adding But how can this be? You are adding more “stuff” to the atom – more protons, more “stuff” to the atom – more protons, electrons, and neutrons to each atom!electrons, and neutrons to each atom!As you stay within a period, the As you stay within a period, the shielding effect stays constant – it shielding effect stays constant – it doesn’t change!doesn’t change! The number of protons increases, The number of protons increases, and therefore the effective nuclear and therefore the effective nuclear charge increases!charge increases!This causes the protons to pull tighter This causes the protons to pull tighter on electrons, causing the atoms to get on electrons, causing the atoms to get smaller!smaller!

Atomic radius increases as we Atomic radius increases as we go down the periodic table…go down the periodic table…

As we go down the periodic table, the shielding effect increasesAs we go down the periodic table, the shielding effect increases This causes the nucleus to pull with less force, causing the atom to become largerThis causes the nucleus to pull with less force, causing the atom to become larger What is the effective nuclear charge of each of these elements in group I?What is the effective nuclear charge of each of these elements in group I? Each element in group I has an effective nuclear charge of +1 Each element in group I has an effective nuclear charge of +1 The group number tells you what the effective nuclear charge is for each element in a groupThe group number tells you what the effective nuclear charge is for each element in a group Does the effective nuclear charge change as we go down a group?Does the effective nuclear charge change as we go down a group? No! Each element in a group has the No! Each element in a group has the same same effective nuclear charge!effective nuclear charge!

HydrogenHydrogenLithiumLithium

SodiumSodiumPotassiumPotassium

Atomic radius or sizeAtomic radius or size

Ionic radiusIonic radius The size of the atom The size of the atom

when it takes or loses when it takes or loses electrons – when it electrons – when it becomes an IONbecomes an ION

Metals always lose Metals always lose electrons and become electrons and become positivepositive

Non-metals always Non-metals always gain electrons and gain electrons and become negativebecome negative

What happens to their What happens to their size, though?size, though?

What happens to metals…?What happens to metals…?

Metals become SMALLER because they lose entire Metals become SMALLER because they lose entire energy levels – energy levels –

Their shielding effect becomes weaker or lessTheir shielding effect becomes weaker or less Their effective nuclear charge increasesTheir effective nuclear charge increases

What happens to non-metals…?What happens to non-metals…? Non-metals become BIGGER when they take electrons…Non-metals become BIGGER when they take electrons… Why?Why? Opposites attract – you have the same number of protons Opposites attract – you have the same number of protons

pulling on electrons, but with more electrons now, the nucleus pulling on electrons, but with more electrons now, the nucleus cannot pull on the electrons as well – cannot pull on the electrons as well –

That is why the atom becomes larger!That is why the atom becomes larger!

Ionization Energy…..Ionization Energy…..

This is the energy This is the energy required to remove an required to remove an electron from an atom!electron from an atom!

It is measured in volts or It is measured in volts or kilojoules of energykilojoules of energy

What kinds of atoms do What kinds of atoms do you think it is really you think it is really TOUGH to take an TOUGH to take an electron away from?electron away from?

What kinds of atoms do What kinds of atoms do you think it is really you think it is really EASY to take an electron EASY to take an electron away from?away from?

Why is this….?Why is this….?

This is the energy This is the energy required to remove an required to remove an electron from an atom!electron from an atom!

It is measured in volts or It is measured in volts or kilojoules of energykilojoules of energy

What kinds of atoms do What kinds of atoms do you think it is really you think it is really TOUGH to take an TOUGH to take an electron away from?electron away from?

What kinds of atoms do What kinds of atoms do you think it is really you think it is really EASY to take an electron EASY to take an electron away from?away from?

Why is this….?Why is this….?Chlorine atom

Hardly any energy - 495.8 kJ!

Lots of energy - 1251.1 kJ!

Sodium atom

Ionization Energy….Ionization Energy….

It takes hardly any It takes hardly any energy to take an energy to take an electron from a electron from a metal…metal…

They have a very low They have a very low effective nuclear effective nuclear charge compared to charge compared to non-metals….non-metals….

What is the effective What is the effective nuclear charge of Na? nuclear charge of Na? What is the effective What is the effective nuclear charge of Cl?nuclear charge of Cl?

SodiumSodium

ChlorineChlorine

10 p+ - 10 e- = +110 p+ - 10 e- = +1

17 p+ - 10 e- = +717 p+ - 10 e- = +7

Ionization Energy….Ionization Energy….

It takes TONS of It takes TONS of energy to take an energy to take an electron from a non-electron from a non-metal…metal…

They don’t want to They don’t want to give any away!give any away!

They have an They have an extremely high extremely high effective nuclear effective nuclear charge….charge….

7 outer electrons - close to 8!

7 outer electrons - close to 8!

Chlorine atom

17 p+ - 10 e- = +7

High effective nuclear charge – holds onto electrons tightly!

17 p+ - 10 e- = +7

High effective nuclear charge – holds onto electrons tightly!

Ionization Energy Ionization Energy increases as we increases as we move across the move across the periodic table…periodic table…

Why?Why? Again – effective Again – effective

nuclear charge nuclear charge increasesincreases

It is harder to remove It is harder to remove an electron from a an electron from a non-metal than a non-metal than a metal because of a metal because of a high effective nuclear high effective nuclear charge!charge!

SodiumSodium

ChlorineChlorine

10 p+ - 10 e- = +110 p+ - 10 e- = +1

17 p+ - 10 e- = +717 p+ - 10 e- = +7

Ionization Energy Ionization Energy decreases as we decreases as we move down the move down the periodic table…periodic table…

Why?Why? Shielding effect Shielding effect

increases!increases! It is easier to remove It is easier to remove

an electron as we an electron as we move down the move down the periodic tableperiodic table

The nucleus is more The nucleus is more shielded, and shielded, and therefore does not therefore does not attract the valence attract the valence electrons as tightly!electrons as tightly!

SodiumSodium

PotassiumPotassium

2 shields2 shields

3 shields3 shields

Electron Affinity….Electron Affinity…. This is the energy absorbed or released when an atom takes an This is the energy absorbed or released when an atom takes an

electron….electron…. It is nicknamed, “love for electrons”It is nicknamed, “love for electrons” The confusing thing – a negative energy means a great love for The confusing thing – a negative energy means a great love for

electronselectrons A positive energy means an atom does not want an electron…A positive energy means an atom does not want an electron… Why is this….?Why is this….? An atom with an electron affinity of -349 kJ/mol loves An atom with an electron affinity of -349 kJ/mol loves

electrons….electrons…. This is because an atom RELEASES energy if it wants an This is because an atom RELEASES energy if it wants an

electron, and will become stableelectron, and will become stable An atom with an electron affinity of +200 kJ/mol does not want An atom with an electron affinity of +200 kJ/mol does not want

electrons…electrons… This is the energy you would have to put into an atom to force it This is the energy you would have to put into an atom to force it

to take an electron that it doesn’t want – to take an electron that it doesn’t want – It would then ABSORB that energy and become unstableIt would then ABSORB that energy and become unstable

This is the energy absorbed or released when an atom takes an This is the energy absorbed or released when an atom takes an electron….electron….

It is nicknamed, “love for electrons”It is nicknamed, “love for electrons” The confusing thing – a negative energy means a great love for The confusing thing – a negative energy means a great love for

electronselectrons A positive energy means an atom does not want an electron…A positive energy means an atom does not want an electron… Why is this….?Why is this….? An atom with an electron affinity of -349 kJ/mol loves An atom with an electron affinity of -349 kJ/mol loves

electrons….electrons…. This is because an atom RELEASES energy if it wants an This is because an atom RELEASES energy if it wants an

electron, and will become stableelectron, and will become stable An atom with an electron affinity of +200 kJ/mol does not want An atom with an electron affinity of +200 kJ/mol does not want

electrons…electrons… This is the energy you would have to put into an atom to force it This is the energy you would have to put into an atom to force it

to take an electron that it doesn’t want – to take an electron that it doesn’t want – It would then ABSORB that energy and become unstableIt would then ABSORB that energy and become unstable

MagnesiumMagnesium

ChlorineChlorine

ENC = 12 p+ - 10 e- = +2ENC = 12 p+ - 10 e- = +2

ENC = 17 p+ - 10 e- = +7ENC = 17 p+ - 10 e- = +7

Low electron affinity = +19 kJ

Low electron affinity = +19 kJ

High electron affinity =

- 349 kJ

High electron affinity =

- 349 kJ

Why?Why? Effective nuclear Effective nuclear

charge increases…charge increases… Atoms hold onto Atoms hold onto

electrons tighter as electrons tighter as we move across the we move across the periodic table…periodic table…

Electron affinity Electron affinity increases, or increases, or

becomes more becomes more negative, as we negative, as we move across the move across the periodic table…periodic table…

BromineBromine Why?Why? Shielding effect Shielding effect

increases…increases… There are more There are more

shields blocking the shields blocking the nucleus from pulling nucleus from pulling and taking new and taking new electronselectrons

ChlorineChlorine2 shields2 shields

3 shields3 shields

Electron affinity Electron affinity decreases, or decreases, or becomes less becomes less

negative, or more negative, or more positive, as we positive, as we move down the move down the periodic table…periodic table… Which

has the lower electron affinity?

Electron Affinity….Electron Affinity….

Electronegativity….Electronegativity…. This is the tendency to pull on an electron in a bond….This is the tendency to pull on an electron in a bond…. What kinds of atoms do you think really pull on electrons What kinds of atoms do you think really pull on electrons

in a bond?in a bond? What kinds of atoms do you think don’t pull on electrons What kinds of atoms do you think don’t pull on electrons

in a bond?in a bond? Why is this….?Why is this….?

This is the tendency to pull on an electron in a bond….This is the tendency to pull on an electron in a bond…. What kinds of atoms do you think really pull on electrons What kinds of atoms do you think really pull on electrons

in a bond?in a bond? What kinds of atoms do you think don’t pull on electrons What kinds of atoms do you think don’t pull on electrons

in a bond?in a bond? Why is this….?Why is this….?

Doesn’t pull on electrons!

Pulls greatly on electrons!

• Nonmetals have high electronegativities, metals have low electronegativities

EN = 3.16EN = .93

• In summary……• As we go across the periodic table:

• Atomic radius decreases, and ionization energy, electron affinity, and electronegativity increase

• As we go down the periodic table:• Atomic radius increases, and ionization energy, electron affinity, and

electronegativity decrease• Why?• Any time a pattern changes as we move across the periodic table, it is due

to a change in effective nuclear charge, as shielding effect does not change• Any time a pattern changes as we move down the periodic table, it is due to

a change in shielding effect, as effective nuclear charge does not change

Effective nuclear charge changes

Shielding effect changes