1. There are 6 patterns or trends we discuss when looking at the periodic table… 1. Reactivity 2. Atomic radius or size 3. Ionic radius 4. Ionization energy 5. Electron Affinity 6. Electronegativity We have already discussed reactivity – let’s look at the other five!

2. Atomic radius or size…. It decreases as we go across the periodic table… It decreases as we go across the periodic table… It increases as we go down the periodic table… It increases as we go down the periodic table… Why….? Why….?

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

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

6. Atomic radius increases as we go down the periodic table… As we go down the periodic table, the shielding effect increases As we go down the periodic table, the shielding effect increases This causes the nucleus to pull with less force, causing the atom to become larger This 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 group The 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 same effective nuclear charge! No! Each element in a group has the same effective nuclear charge! Hydrogen Lithium Sodium Potassium

7. Atomic radius or size

8. Ionic radius The size of the atom when it takes or loses electrons – when it becomes an ION The size of the atom when it takes or loses electrons – when it becomes an ION Metals always lose electrons and become positive Metals always lose electrons and become positive Non-metals always gain electrons and become negative Non-metals always gain electrons and become negative What happens to their size, though? What happens to their size, though?

9. What happens to metals…? Metals become SMALLER because they lose entire energy levels – Metals become SMALLER because they lose entire energy levels – Their shielding effect becomes weaker or less Their shielding effect becomes weaker or less Their effective nuclear charge increases Their effective nuclear charge increases

10. 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 pulling on electrons, but with more electrons now, the nucleus cannot pull on the electrons as well – Opposites attract – you have the same number of protons pulling on electrons, but with more electrons now, the nucleus cannot pull on the electrons as well – That is why the atom becomes larger! That is why the atom becomes larger!

11. Ionization Energy….. This is the energy required to remove an electron from an atom! This is the energy required to remove an electron from an atom! It is measured in volts or kilojoules of energy It is measured in volts or kilojoules of energy What kinds of atoms do you think it is really TOUGH to take an electron away from? What kinds of atoms do you think it is really TOUGH to take an electron away from? What kinds of atoms do you think it is really EASY to take an electron away from? What kinds of atoms do you think it is really EASY to take an electron away from? Why is this….? Why is this….? This is the energy required to remove an electron from an atom! This is the energy required to remove an electron from an atom! It is measured in volts or kilojoules of energy It is measured in volts or kilojoules of energy What kinds of atoms do you think it is really TOUGH to take an electron away from? What kinds of atoms do you think it is really TOUGH to take an electron away from? What kinds of atoms do you think it is really EASY to take an electron away from? What kinds of atoms do you think it is really EASY to take an electron away from? Why is this….? Why is this….? Chlorine atom Hardly any energy - 495.8 kJ! Lots of energy - 1251.1 kJ! Sodium atom

12. Ionization Energy…. It takes hardly any energy to take an electron from a metal… It takes hardly any energy to take an electron from a metal… They have a very low effective nuclear charge compared to non-metals…. They have a very low effective nuclear charge compared to non-metals…. What is the effective nuclear charge of Na? What is the effective nuclear charge of Cl? What is the effective nuclear charge of Na? What is the effective nuclear charge of Cl? Sodium Chlorine 10 p + - 10 e - = +1 17 p + - 10 e - = +7

13. Ionization Energy…. It takes TONS of energy to take an electron from a non- metal… It takes TONS of energy to take an electron from a non- metal… They don’t want to give any away! They don’t want to give any away! They have an extremely high effective nuclear charge…. They have an extremely high effective nuclear charge…. 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!

14. Ionization Energy increases as we move across the periodic table… Why? Why? Again – effective nuclear charge increases Again – effective nuclear charge increases It is harder to remove an electron from a non-metal than a metal because of a high effective nuclear charge! It is harder to remove an electron from a non-metal than a metal because of a high effective nuclear charge! Sodium Chlorine 10 p + - 10 e - = +1 17 p + - 10 e - = +7

15. Ionization Energy decreases as we move down the periodic table… Why? Why? Shielding effect increases! Shielding effect increases! It is easier to remove an electron as we move down the periodic table It is easier to remove an electron as we move down the periodic table The nucleus is more shielded, and therefore does not attract the valence electrons as tightly! The nucleus is more shielded, and therefore does not attract the valence electrons as tightly! Sodium Potassium 2 shields 3 shields

17. Electron Affinity…. This is the energy absorbed or released when an atom takes an electron…. This is the energy absorbed or released when an atom takes an electron…. It is nicknamed, “love for electrons” It is nicknamed, “love for electrons” The confusing thing – a negative energy means a great love for electrons The confusing thing – a negative energy means a great love for electrons 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 electrons…. An atom with an electron affinity of -349 kJ/mol loves electrons…. This is because an atom RELEASES energy if it wants an electron, and will become stable This is because an atom RELEASES energy if it wants an electron, and will become stable An atom with an electron affinity of +200 kJ/mol does not want electrons… An atom with an electron affinity of +200 kJ/mol does not want electrons… This is the energy you would have to put into an atom to force it to take an electron that it doesn’t want – This is the energy you would have to put into an atom to force it to take an electron that it doesn’t want – It would then ABSORB that energy and become unstable It would then ABSORB that energy and become unstable This is the energy absorbed or released when an atom takes an electron…. This is the energy absorbed or released when an atom takes an electron…. It is nicknamed, “love for electrons” It is nicknamed, “love for electrons” The confusing thing – a negative energy means a great love for electrons The confusing thing – a negative energy means a great love for electrons 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 electrons…. An atom with an electron affinity of -349 kJ/mol loves electrons…. This is because an atom RELEASES energy if it wants an electron, and will become stable This is because an atom RELEASES energy if it wants an electron, and will become stable An atom with an electron affinity of +200 kJ/mol does not want electrons… An atom with an electron affinity of +200 kJ/mol does not want electrons… This is the energy you would have to put into an atom to force it to take an electron that it doesn’t want – This is the energy you would have to put into an atom to force it to take an electron that it doesn’t want – It would then ABSORB that energy and become unstable It would then ABSORB that energy and become unstable

18. Magnesium Chlorine ENC = 12 p + - 10 e - = +2 ENC = 17 p + - 10 e - = +7 Low electron affinity = +19 kJ High electron affinity = - 349 kJ High electron affinity = - 349 kJ Why? Why? Effective nuclear charge increases… Effective nuclear charge increases… Atoms hold onto electrons tighter as we move across the periodic table… Atoms hold onto electrons tighter as we move across the periodic table… Electron affinity increases, or becomes more negative, as we move across the periodic table…

19. Bromine Why? Why? Shielding effect increases… Shielding effect increases… There are more shields blocking the nucleus from pulling and taking new electrons There are more shields blocking the nucleus from pulling and taking new electrons Chlorine 2 shields 3 shields Electron affinity decreases, or becomes less negative, or more positive, as we move down the periodic table… Which has the lower electron affinity?

20. Electron Affinity….

21. 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 in a bond? What kinds of atoms do you think really pull on electrons in a bond? What kinds of atoms do you think don’t pull on electrons in a bond? What kinds of atoms do you think don’t pull on electrons 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 in a bond? What kinds of atoms do you think really pull on electrons in a bond? What kinds of atoms do you think don’t pull on electrons in a bond? What kinds of atoms do you think don’t pull on electrons in a bond? Why is this….? Why is this….? Doesn’t pull on electrons! Pulls greatly on electrons!

22. Nonmetals have high electronegativities, metals have low electronegativities EN = 3.16EN =.93

24. 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