3.4 Periodic Trends from past papers Flashcards
Explain why the electronegativity of chlorine is greater than that of phosphorous.
Both have the same number of electron shells (3), so experience the same amount of shielding and the valence electrons are in the same energy level. Cl has a greater nuclear charge than P, therefore has a greater electrostatic attraction to the pair of bonding electrons and a greater electronegativity.
Explain why the radius of the Cl atom and the radius of the Cl- ion are different
Cl atom: 99 pm
Cl- ion: 181 pm
The Cl- ion has a bigger radius than the Cl atom. Cl- has gained an electron so there is more electron repulsion in the valence shell, and electrons are physically further from the nucleus. The nuclear charge is the same so there is less attraction between the nucleus and the valence electrons, and Cl- is larger.
What is the definition of first ionisation energy?
What is the trend in first ionisation energy down a group?
What is the trend in first ionisation energy across a period?
The first ionisation energy is the energy required to remove one mole of the valence electrons from one mole of gaseous atoms.
The first ionisation energy decreases going down the group.
The first ionisation energy increases across a period.
What is the definition of electronegativity?
What is the trend in electronegativity down a group?
What is the trend in electronegativity across a period?
Electronegativity is a measure of the attraction an atom has for a bonding pair of electrons.
The electronegativity decreases going down the group.
The electronegativity increases across a period.
The following **[graph] shows the first ionisation energies of the Group 2 elements from Be to Ba.
Be: 900 kJ/mol
Mg: 750 kJ/mol
Ca: 600 kJ/mol
Sr: 550 kJ/mol
Ba: 500 kJ/mol
Explain the trend shown of first ionisation energies of the group two elements.
**[This website won’t let me add pictures, so I roughly estimated the values from reading the simple graph provided]
The first ionisation energy is the energy required to remove one mole of the valence electrons from one mole of gaseous atoms.
The trend is that the ionisation energy decreases going down the group two elements.
As you go down the group, each atom has an extra shell, so it experiences more shielding and the valence electrons are in different energy levels. Although the nuclear charge is increasing, the extra shielding and further distance between the nucleus and valence shells means there is less electrostatic attraction. The further down the group you go, the less energy is required to remove electrons.
Explain the factors influencing the trends in electronegativity and first ionisation energy down a group of the periodic table
● Define both electronegativity and first ionisation energy
● Explain the trend in both electronegativity and first ionisation energy down a group
● Compare the trend in electronegativity and first ionisation energy down a group
Electronegativity is a measure of the attraction an atom has for a bonding pair of electrons.
The first ionisation energy is the energy required to remove one mole of the valence electrons from one mole of gaseous atoms.
Both First Ionisation Energy and Electronegativity decreases down a group.
As you go down the group, each atom has an extra shell, so it experiences more shielding and the valence electrons are in different energy levels. Although the nuclear charge is increasing, the extra shielding and further distance between the nucleus and valence shells means there is less electrostatic attraction between the nucleus and the outer electrons.
There is therefore less attraction for the pair of bonding electrons (so electronegativity is smaller), and it becomes easier to remove an electron down a group (so first ionisation energy is also smaller).
Justify the trends in first ionisation energies for the elements in the third period of the periodic table.
Relate this to the expected trend in atomic radii across the third period.
Element First ionisation energy/ kJ/mol
Na 502
Al 584
Si 793
Ar 1,527
The first ionisation energy is the energy required to remove one mole of the valence electrons from one mole of gaseous atoms.
The first ionisation energy increases as you go across the period, and the radius decreases as you go across the period.
Period three elements have the same number of electron shells (3), so experience the same amount of shielding and the valence electrons are in the same energy level. As you go across the group, the nuclear charge is increasing. The electrostatic attraction between the nucleus and the valence electrons increases and therefore it is more difficult to remove an electron (first ionisation energy is higher), and the atom is smaller (atomic radius decreases).
Explain the difference between the radii of the K atom and the K+ ion.
The K+ ion has a smaller radius than the K atom. K+ has lost an electron and therefore lost a whole shell. It experiences less shielding, and the valence electrons are physically closer to the nucleus. The nuclear charge is the same, so there is a greater attraction between the nucleus and the valence electrons, and K+ is smaller.
Using your knowledge of the trends in the periodic table, which atoms has the greater electronegativity value out of:
Br and I
Br has a greater electronegativity than I. Br has one less shell, so it experiences less shielding and the valence electrons are in different energy levels.
Although I has a greater nuclear charge than Br, it has less attraction for the pair of bonding electrons so Br has a larger electronegativity value than I.
I has an extra shell, so it experiences more shielding and the valence electrons are in different energy levels. Although it has a greater nuclear charge than Br, I has less attraction for the pair of bonding electrons so has a smaller electronegativity value.
Discuss the following data:
Atom Electronegativity
O 3.44
Se 2.55
Se has two extra shells, so it experiences more shielding and the valence electrons are in different energy levels. Although it has a greater nuclear charge than O, Se has less attraction for the pair of bonding electrons so has a smaller electronegativity value.
Discuss the following data:
Atom or ion Radius/ pm
Cl 99
Cl- 181
The Cl- ion has a bigger radius than the Cl atom. Cl- has gained an electron so there is more electron repulsion in the valence shell, and electrons are physically further from the nucleus. The nuclear charge is the same so there is less attraction between the nucleus and the valence electrons, and Cl- is larger.
Discuss the following data:
Atom First ionisation energy/ kJ/mol
Li 526
Cl 1,257
Cl has a greater nuclear charge than Li. Therefore there is a greater attraction between the nucleus and outer electrons/electrons held more tightly so it is harder to remove an electron from Cl than Li. Even though Cl has an sheel, the extra shielding is not as significant as the effect of the increased nuclear charge, so Cl has a higher first ionisation energy than Li.
Explain why the radii of the S atom and the S2- ion are different.
Radius/ pm S atom 104 S2- ion 184
The S2- ion has a bigger radius than the S atom. S2- has gained an electron so there is more electron repulsion in the valence shell, and electrons are physically further from the nucleus. The nuclear charge is the same so there is less attraction between the nucleus and the valence electrons, and S2- is larger.
Discuss the difference in electronegativities for oxygen, sodium and sulfur.
Element Electronegativity
O 3.44
Na 0.93
S 2.58
Electronegativity increases across a period, and decreases down a group.
Na and S have the same number of electron shells (3), so experience the same amount of shielding and the valence electrons are in the same energy level. S has a greater nuclear charge therefore has a greater electrostatic attraction between the nucleus and a pair of bonding electrons and a greater electronegativity.
O and S are in the same group. S has an extra shell, so it experiences more shielding and the valence electrons are in different energy levels. Although it has a greater nuclear charge than O, S has less attraction for the pair of bonding electrons so has a smaller electronegativity value
