Atomic properties and periodicity
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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
What is the effect of Z* on atomic radii?
Similar properties down the same group Increase in the value of n for the highest-energy electrons Increase in the overall size of the atom
What are valence electrons important for?
They are responsible for the chemical properties of the atom and are involved in chemical bonding
What are the core electrons important for?
Act as a shield for valence electrons
Why don’t we need to write core electrons in electron configuration?
They do not play an important part in bonding or chemistry
What is the definition of ionisation energy?
Energy required to remove the highest-energy electron from the atom in the gas phase to produce a cation
What are the trends down group 1?
Small decrease in ionisation energy Increase in atom size Similar physical and chemical properties
What are the trends across the first row?
Z* increases rapidly Large increase in ionization energy across the row Decrease in atom size
When going down a group, how does Z* increase?
Slowly
When going across a row, how does Z* increase?
Quickly