Atomic orbitals, electronic configurations and the periodic table Flashcards
How can the discrete lines observed in atomic spectra be explained
The discrete lines observed in atomic spectra can be explained if electrons, like photons, also display the properties of both particles and waves.
How do electrons behave
Electrons behave as standing (stationary) waves in an atom.
What are standing (stationary) waves
These are waves that vibrate in time but do not move in space.
What are orbitals
There are different sizes and shapes of standing wave possible around the nucleus, known as orbitals.
What is the maximum number of electrons orbitals can hold
Orbitals can hold a maximum of two electrons.
What different shapes are orbitals identified as
The different shapes of orbitals are identified as s, p, d and f (knowledge of the shape of f orbitals is not required).
What is quanta
Electrons within atoms have fixed amounts of energy called quanta.
It is possible to describe any electron in an atom using four quantum numbers:
- the principal quantum number
- the angular momentum quantum number
- the magnetic quantum number
- the spin magnetic quantum number
The principal quantum number
the principal quantum number n indicates the main energy level for an electron and is related to the size of the orbital
The angular momentum quantum number
the angular momentum quantum number l determines the shape of the subshell and can have values from zero to n − 1
The spin magnetic quantum number
the spin magnetic quantum number ms determines the direction of spin and can have
valuesof +1/2 or −1/2
Electrons within atoms are arranged according to
- the aufbau principle
- Hund’s rule
- the Pauli exclusion principal
The aufbau principal
the aufbau principle — electrons fill orbitals in order of increasing energy (‘aufbau’ means ‘building up’ in German)
Hund’s rule
Hund’s rule — when degenerate orbitals are available, electrons fill each singly, keeping their spins parallel before spin pairing starts
The Pauli exclusion principal
the Pauli exclusion principle — no two electrons in one atom can have the same set of four quantum numbers, therefore, no orbital can hold more than two electrons and these two electrons must have opposite spins
In an isolated atom what are the orbitals within each sub shell
In an isolated atom the orbitals within each subshell are degenerate.
How can the relative energies corresponding to each orbital be represented
The relative energies corresponding to each orbital can be represented diagrammatically using orbital box notation for the first four shells of a multi-electron atom.
What elements can electronic configurations be written for
Electronic configurations using spectroscopic notation and orbital box notation can be written for elements of atomic numbers 1 to 36.
What four blocks is the periodic table divided into
The periodic table is subdivided into four blocks (s, p, d and f) corresponding to the outer electronic configurations of the elements within these blocks.
What is associated with half filled and full sub shells
There is a special stability associated with half-filled and full subshells.
The more stable the electronic configuration …
The more stable the electronic configuration the higher the ionisation energy
What is VSEPR theory used for
VSEPR (valence shell electron pair repulsion) theory can be used to predict the shapes of molecules and polyatomic ions.
The number of electron pairs surrounding a central atom can be found by:
- taking the total number of valence (outer) electrons on the central atom and adding one for each atom attached
- adding an electron for every negative charge
- removing an electron for every positive charge
- dividing the total number of electrons by two to give the number of electron pairs
How are electron pairs arranged
Electron pairs are negatively charged and repel each other. They are arranged to minimise repulsion and maximise separation.
The arrangement of electron pairs around a central atom is:
- linear for two electron pairs
- trigonal planar for three electron pairs
- tetrahedral for four electron pairs
- trigonal bipyramidal for five electron pairs
- octahedral for six electron pairs
How are Shapes of molecules or polyatomic ions determined
Shapes of molecules or polyatomic ions are determined by the shapes adopted by the atoms present based on the arrangement of electron pairs. Electron dot diagrams can be used to show these arrangements.
Electron pair repulsions decrease in strength in the order:
non-bonding pair/non-bonding pair > non-bonding pair/bonding pair > bonding pair/bonding pair
The magnetic quantum number
Determines the orientation of the orbital can have values from -1 and +1
How to write quantum number
n = principal qn number - what energy level 1st 2nd 3rd
l= angular momentum - what type of atomic orbital s(0) p(1) d (2) f(3)
m = magnetic qn - which specific orbital s(0) px (-1) py(0) pz(+1) dx2 (-2) dx2y2 (-1) dxy (0) dyz (+1) dxz (+2)
M = spin - which spin +1/2 -1/2
What are the shapes and max amount of electrons the orbitals can hold
S - sphere x1
P- dumbell x3
d - double dumbell x5
Increasing energy
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6
