L2b_ElectronCofiguration_September2014
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Transcript of L2b_ElectronCofiguration_September2014
Atom , of all matter, consists of 3 fundamental particles:• Electrons• Protons• Neutrons Nucle
us
Shell
How do electron organise themselves in an atom?
BOHR MODELIn the Bohr model, electrons are viewed as particles traveling along circular orbits of fixed radius
QUANTUM MECHANICAL MODEL
•Electrons are viewed as waves rather than particles
•These waves are considered to be spread out through a region of space called an orbital.
Quantum mechanic model
An orbital: quantum mechanical equivalent of electron location
Wave function: a mathematical description of a wave
Schrödinger equation: HΨn=EnΨn
H: complex mathematical operatorE: energyΨ: wave function of electron
Further reading can be found in ‘Chemistry for Engineering Students’
Schrödinger equation: describes the energy of electrons
What can we see when we solve Schrödinger equation for an atom?
Ψ: wave function of electron is very complicated
From the wave function, we can get mathematical equation for atomic orbital, to describe this:
Quantum numbers:
Primary quantum number (n)
Secondary quantum number (l)
Magnetic quantum number (ml)
1. Primary quantum number (n) = shell• defines the shell in which a particular orbital is found• must be a positive integer (n = 1, 2, 3, 4, 5,……) When n=1: first shell
n=2: second shell
When number of electron >1 in a shell:• Repulsion between negative charges
Energy difference between orbital in a shell
2. Secondary quantum number (l) = subshell• provides a way to describe energy different
between the orbitals• l : 0, 1, 2, 3, …., n-1
3. Magnetic quantum number (ml):Possible values: from – l to +l
Under normal conditions, atoms can be specified by n and l. Under magnetic field:
How many electrons can occupy an orbital?
The Pauli exclusion principle states that: no two electrons in an atom may the same set of four quantum numbers: n, l, ml and ms.
THE SPIN QUANTUM NUMBER (MS).When placed in a strong magnetic field, electrons behave like tiny magnets.
Spin up+1/2
Spin down-1/2
Electron configuration
• Fill orbitals with lowest energy – highest energy: the aufbau principle
1H 3Li
1s2 2s1
1s1
• Hund’s rule: within a subshell, electrons occupy orbitals individually whenever possible.
2p6C
1s
2s
2p
Highest energy
lowest energy
The Periodic Table and Electron Configuration
• Electron of the highest energy orbital comes from the same subshell
Periodic trends in Atomic properties
Atomic size: explore the trends in the periodic table• within a group• within a period
Decrease
Carbon
Attraction Repulsion
Shielding: the masking of the nuclear charge by other electrons
Effective nuclear charge= Attraction - repulsion
Atomic size:• within a period:
Increase in atomic number (positively charge nuclear)
increase in the attraction forces (effective nuclear charge) between nucleus and electrons
decrease in atomic size
+ -Attraction
+ +Repulsion
Ionisation( or Ionization) energy
Ionisation energy: the energy required to remove an electron from an atom, forming a cation
First Ionisation energy: the amount of energy needed to induce the reaction
X(gas) X+(gas) + e-
Second Ionisation energy: the amount of energy needed to induce the reaction
X+(gas) X2+(gas) + e-
Electron affinity : the energy required to add an electron to an atom, forming an anion
X(gas) + e- X-(gas) Ionisation energy: always positiveElectron affinity : could be negative or positive
• If X- NOT stable:
Requireenergy
X(gas) + e- X-(gas)
• If X- stable: X(gas) + e- X-(gas)
Release energy
Negative amount of energy
Negative electron affinity
Positive electron affinity
Most electron affinity values are negative