Atomic properties and periodicity Flashcards
What is the electrostatic effect like in many-electron atoms?
Electrons feel electrostatic attraction to the nucleus and repulsion from other electrons
This means the net attraction to the nucleus is reduced
Each electron is partially shielded
What is the equation to work out effective nuclear charge?
= “true” nuclear charge - shielding
What symbol is given to nuclear charge?
Z
What symbol is given to effective nuclear charge?
Z*
What symbol is given to shielding?
σ
Why is the energy to remove the first electron lower than the energy to remove the second?
Lower due to repulsion from the second electron and shielding
What are the two effects of penetration of 2s close to the nuclear?
- Increases the nuclear attraction for a 2s electron over that of 2p
- Decrease the shielding of 2s electrons by 1s electrons
Why is the effective nuclear charge of a 2s electron greater than that of a 2p?
2s is more stable
The energy of a 2s orbital is lower than that of a 2p
What does the lobe do and act as?
Penetrates and acts as a shield
What does shielding and penetration result in?
The splitting of orbitals with the same principle quantum number into different energy leveks
What are Slater’s rules used for?
To calculate effective nuclear charge values
What is the first of Slater’s rules?
Write the electronconfiguration of the atom and group the orbitals as [1s] [2s,2p] etc, putting s and p together
What are the contributions for total shielding (σ) used by Slater? (Rule 2)
0 from all electrons in groups to the right
0.35 from each of the electrons in the same group (ns, np)
0.3 for 1s
0.85 from each electron in the n-1 shell
1 from each electron in lower shells
What is the third of Slater’s rules?
The shielding is then subtracted from the nuclear charge (Z) to find the effective nuclear charge (Z*)
Example. Calculate the effective nuclear charge of Mg? Z=12
[1s²][2s²,2p⁶][3s²]
= (1x0.35) + (8x0.85) + (2x1) = 9.15
= 12-9.15 = 2.85
