Structure and Bonding Flashcards
What is covalent bonding?
Formal sharing of electrons between atoms, covalent bonds are found in elements with high electronegativities
What is ionic bonding?
Bonds formed between elements that have relatively high differences in electronegativities, electrons are transferred to another atom instead of being shared between two
What is metallic bonding?
Found in elements that have low electronegativities, electrons are delocalised into a sea of electrons and positive metal ions are attracted to the electrons by electrostatic forces of attraction
What is the van Arkel-Ketelaar triangle?
- A triangle that predicts which type of bonding will occur between elements based on their electronegativities
- Along the bottom of the triangle is the electronegativity
- Along the side of the triangle is the difference in electronegativity between the two elements
Which type of bonding is predicted between two elements in the bottom left of the van Arkel-Ketelaar triangle?
Metallic, low electronegativity and low difference in electronegativity
Which type of bonding is predicted between two elements in the bottom right of the van Arkel-Ketelaar triangle?
Covalent, high electronegativity but not much difference in electronegativity
Which type of bonding is predicted between two elements at the top of the van Arkel-Ketelaar triangle?
Ionic, there is a big difference in electronegativity between the two elements
Using the van Arkel-Ketelaar triangle, how can you predict the type of bonding based on the difference in electronegativity?
- ΔX > 2 = ionic
- 0.5 < ΔX < 2 = polar covalent
- ΔX < 0.5 = covalent or metallic
In an enthalpy change of formation reaction, does the system want to lose or gain energy?
Lose energy, it is thermodynamically favourable for the reaction to be exothermic as the products are more stable than the reactants
What is the trend in ionisation energy as you move across a period?
Ionisation energy increases as the effective nuclear charge increases, the atomic radius also decreases which makes it harder to remove an electron as the electron is closer to the nucleus and experiences a greater force of attraction from the nucleus, this means ionisation energy increases
Why does ionisation energy decrease between Be and B?
When you move from Be to B the valence electron is now in a 2p orbital rather than the 2s orbital, this means that the valence electron of B experiences shielding from the 2s orbital and therefore it is easier to remove an electron and therefore ionisation decreases
Why does ionisation energy decrease between N and O?
The p orbitals of nitrogen are all half filled and there is no spin pairing, in oxygen it has 2 half filled p orbitals and one full p orbital, this means that one of its p orbitals is spin paired and its valence electron experiences repulsion and its easier to remove therefore it has lower ionisation energy
What is the trend in ionisation energy going down the group?
As you go down the group ionisation energy decreases as atomic radius increases, this means that electrons are further away from the nucleus and although they experience a greater effective nuclear charge going down the group, the distance from the nucleus is more significant and means that electrons experience a weaker attraction from the nucleus as you go down the group
When you move from K to Rb in group 1, why does the effective nuclear charge increase more than expected?
The effective nuclear charge increases more than expected as the 10 added electrons in the 3d orbital don’t effectively shield the 10 added protons, hence why there is a greater effective nuclear charge than expected
What is the trend in successive ionisation energy?
- As you go from first to second ionisation energies there is a dramatic increase, this is because there is a stronger attraction between the valence electron and a cation
- As you get to a lower shell, there is a huge increase in ionisation energy as the electrons are now closer to the nucleus and there are more protons than electrons so effective nuclear charge increases
What is the trend in electron gain enthalpy as you move across a period?
Electron gain enthalpy becomes more exothermic as you move across a period, this is because the force of attraction between the nucleus and the electron increases as effective nuclear charge increases and atomic radius decreases. This makes it easier to add an electron and a stronger bond is formed and therefore more energy is released
Why is the electron gain enthalpy less exothermic than expected when adding an electron to Be?
When adding an electron to Be, it is added to the 2p orbital meaning it experiences more shielding and therefore a weaker bond is formed between the nucleus and the electron and therefore less energy is released
Why is the electron gain enthalpy less exothermic than expected when adding an electron to N?
Nitrogen’s p orbitals are all half filled, when you add an electron one of the orbitals becomes full and spin pairing occurs. This means that the added electron experiences repulsion and therefore a weaker bond is formed and less energy is released
What is the trend in electron gain enthalpy going down the group?
As you go down the group, the force of attraction from the nucleus decreases as the atomic radius increases and shielding increases. This means that electrons are attracted less and they form weaker bonds with the nucleus and less energy is released. Therefore electron gain enthalpy becomes less exothermic as you go down the group
What is the trend in lattice enthalpy involving ionic charge and size of ions?
- As the size of the ions increases, the lattice enthalpy becomes less exothermic, this is because there is a weaker attraction between as the ions can’t get as close together
- As ionic charge increases, lattice enthalpy becomes more exothermic as there is a stronger attraction between ions meaning more energy is released
What is the equation for the proportionality of lattice enthalpy?
- Lattice enthalpy ∝ [ |Z+| x |Z-| ] / [ r+ + r- ]
- Z = charge
- r = radius
What happens to lattice enthalpy going down the group?
- If you keep one ion the same and vary the other ion by going down the group, lattice enthalpy becomes less exothermic due to the size of the ion decreasing down the group meaning that the bond between the ions is weaker and therefore less energy is released
- Although the lattice enthalpy decreases down the group, it is still always exothermic due to the ionisation energy of the elements involved in forming the lattice decreasing as well. The net change of the system is always negative.
Why do the noble gases not form compounds readily?
The first ionisation energy of the noble gases is extremely high meaning that the bonds formed in the compound of the noble gas have to be very strong so that more energy is released forming the bonds than was required to form an ion of the noble gas
