Main Group Chemistry Flashcards
Define effective nuclear charge
The charge felt by the outer electrons. Often shielded by the inner electrons
Define ionisation energy
The ease with which electrons can be removed from the outer shell
Define electron affinity
The gaining of electron enthalpy
How to calculate the shielding constant and thus the effective nuclear charge
Z = no. of protons - shielding constant
S = 0.35(no. of electrons in same shell) + 0.85(no. of electrons in n-1 shell) + 1.00*(no. of electrons in n-2 shell)
Define electro negativity
The ability of an atom to attract electron density towards itself in a molecule
What is Allen’s definition of electronegativity
The average energy of the outer shell electrons when the atom is in its ground state
What is Mullikens definition of electrons negativity (equation)
Eneg = (ionisation energy + electron affinity)/2
What is A&R definition of electronegativity?
Eneg = (effective nuclear charge)/radius^2
How does effective nuclear charge change across the PT
Across PT - increases
Down PT - no comparison possible as e further from the nucleus
How does ionisation energy change across the PT
Across PT - increase (expect O as half filled subshell is more favourable)
Down PT - decreases down PT as e further from nucleus
How does electron affinity change across the periodic table?
Across PT - increases (except nitrogen as half filled subshell more stable)
Move +ve = more stabilising
What are the two major defining values for the bonding type?
Delta X = X(A) - X(B)
Sigma X = (X(A) + X(B))/2
Characteristics of Ionic bonding
Delta X is large
Non directional electrostatic interactions
MP very high
Large lattice energy
Characteristics of metallic bonding
Sigma C is low
Delocalised electrons on closely packed spheres
Low ionisation E
Large atomic size
Probability of metal formation = atomic radius/ionisation energy
Characteristics of covalent bonding
Sigma X is high
Delta X is small
Directional bond
