CEM 141 EXAM 3 QUESTIONS & ANSWERS
1. Lecture 2-8: Periodic Trends - Ionization Energies
2. Ionization Energy: energy required to remove an electron from an atom in the gas phase
Li(g) --> Li+(g) + e- (IE=520 kJ/mol)
X + energy ’X+ + e−
where X is any atom or molecule capable of being ionized, X+ is that atom or molecule with an electron removed, and e−
is the removed electron.
3. Is it easier to remove an electron from Li or Na?: Na
4. Is the ionization energy of Li larger or smaller than that of Na?: Larger, bc you have
to overcome stronger electrostatic forces
5. Ionization Energy Decreases Down a Group: The I.E. of lithium is 520
kJ/mol. The I.E. of sodium (Na) is 495 kJ/mol.
It takes MORE energy to remove an electron from Li than from Na
6. Ionization Energy Across a Row
Is it easier to remove an electron from Li or Ne?
Is the ionization energy of Li larger are smaller than that of Ne?: Li, the ettective nuclear
charge
Smaller
7. Ionization Energy Increases Across a Row: The I.E. of Li is 520
kJ/mol The I.E. of Ne is 2080.6 kJ/mol
Bc of the increase in ettective nuclear charge --> smaller atom --> impacts denominator of Coloumb's law
8. Ionization Energy in second row: Dip in boron dip in oxygen
9. Recap: Trends down a group: Atom radius
increases IE decreases
Why?
As we move down a group, the orbitals become larger. However, the ettective nuclear charge does not change. On average,
,the outermost electron will be further from the nucleus (but feel the same ettective nuclear charge) so the attractive force will
be weaker.
10. Recap: Trends across a row: Atomic radius decreases
Ionization energy
increases Why?
Across a row, the ettective nuclear charge increases. Atoms w/ higher ENCs "hold on to their electrons" more tightly.
,11. Periodic trends in atomic radius and ionization energy: Small ms have higher
ato ionization energies
They are inversely related
are found
But caused by the phenomena - the ettective nuclear charge and shell in which valence electrons
12. Ionization energy second row, why not a smooth rise?:
13. Which electron is being removed from B?
A. 2s1
B. 2s2
C. 2p1
D. 2p2: C. 2p1
Which electron is removed from O?: C - electrons won't double up unless t hey have to.
14.
15. It is easier than expected to remove:: The lone electron from a p orbital (eg B or group 13) -
Why? Because the two s electrons are more tightly held to the nucleus and more diflcult to remove.
The first paired electron from group 16 (O,S, etc.) - Why? Because there is a slight repulsion when an electron pairs up in
an orbital - which makes it easier to remove
16. You can remove more than one electron: Second ionization energy
X+(g) + energy ------ > X^(2+)(g) + e-
Third IE
X^(2)+(g)-->X^(3)+e-
17. Which ionization energy is larger?
1. First
2. Second
, 3. Third: Third =
7730 kJ/mol
Second = 1450
kJ/mol
First = 738 kJ/mol
18. Note that huge jump for the 3rd ionization energy of Mg, why?: Because that
electron is being removed from the core. Core electrons are harder to remove.
19. Ionization energies are affected by....: Size of atom/ion (smaller size --> higher IE)
Size of positive charge for cations (larger charge --> larger IE)
1. Lecture 2-8: Periodic Trends - Ionization Energies
2. Ionization Energy: energy required to remove an electron from an atom in the gas phase
Li(g) --> Li+(g) + e- (IE=520 kJ/mol)
X + energy ’X+ + e−
where X is any atom or molecule capable of being ionized, X+ is that atom or molecule with an electron removed, and e−
is the removed electron.
3. Is it easier to remove an electron from Li or Na?: Na
4. Is the ionization energy of Li larger or smaller than that of Na?: Larger, bc you have
to overcome stronger electrostatic forces
5. Ionization Energy Decreases Down a Group: The I.E. of lithium is 520
kJ/mol. The I.E. of sodium (Na) is 495 kJ/mol.
It takes MORE energy to remove an electron from Li than from Na
6. Ionization Energy Across a Row
Is it easier to remove an electron from Li or Ne?
Is the ionization energy of Li larger are smaller than that of Ne?: Li, the ettective nuclear
charge
Smaller
7. Ionization Energy Increases Across a Row: The I.E. of Li is 520
kJ/mol The I.E. of Ne is 2080.6 kJ/mol
Bc of the increase in ettective nuclear charge --> smaller atom --> impacts denominator of Coloumb's law
8. Ionization Energy in second row: Dip in boron dip in oxygen
9. Recap: Trends down a group: Atom radius
increases IE decreases
Why?
As we move down a group, the orbitals become larger. However, the ettective nuclear charge does not change. On average,
,the outermost electron will be further from the nucleus (but feel the same ettective nuclear charge) so the attractive force will
be weaker.
10. Recap: Trends across a row: Atomic radius decreases
Ionization energy
increases Why?
Across a row, the ettective nuclear charge increases. Atoms w/ higher ENCs "hold on to their electrons" more tightly.
,11. Periodic trends in atomic radius and ionization energy: Small ms have higher
ato ionization energies
They are inversely related
are found
But caused by the phenomena - the ettective nuclear charge and shell in which valence electrons
12. Ionization energy second row, why not a smooth rise?:
13. Which electron is being removed from B?
A. 2s1
B. 2s2
C. 2p1
D. 2p2: C. 2p1
Which electron is removed from O?: C - electrons won't double up unless t hey have to.
14.
15. It is easier than expected to remove:: The lone electron from a p orbital (eg B or group 13) -
Why? Because the two s electrons are more tightly held to the nucleus and more diflcult to remove.
The first paired electron from group 16 (O,S, etc.) - Why? Because there is a slight repulsion when an electron pairs up in
an orbital - which makes it easier to remove
16. You can remove more than one electron: Second ionization energy
X+(g) + energy ------ > X^(2+)(g) + e-
Third IE
X^(2)+(g)-->X^(3)+e-
17. Which ionization energy is larger?
1. First
2. Second
, 3. Third: Third =
7730 kJ/mol
Second = 1450
kJ/mol
First = 738 kJ/mol
18. Note that huge jump for the 3rd ionization energy of Mg, why?: Because that
electron is being removed from the core. Core electrons are harder to remove.
19. Ionization energies are affected by....: Size of atom/ion (smaller size --> higher IE)
Size of positive charge for cations (larger charge --> larger IE)
