chemistry - 1.2 Flashcards
How can the discrete lines observed in atomic spectra be explained?
If electrons, like photons, also display the properties of both particles and waves.
What do electrons behave as in an atom?
‘Stationary waves’, waves that vibrate in time but do not move in space.
What are orbitals?
Different sizes and shapes of standing wave possible around the nucleus.
What are the different shapes of orbitals identified as?
s, p, d and f
What do electrons within atoms have?
Fixed amounts of energy called quanta.
How can you describe any electron in an atom?
Using four quantum numbers.
What does the principal quantum number ‘n’ indicate?
The main energy level for an electron and is related to the size of the orbital.
What does the angular momentum number ‘l’ determine?
The shape of the sub shell and can have values from zero to n-1.
What does the magnetic quantum number ‘ml’ determine?
The orientation of th orbital and can have values between - l and + l.
What does the spin magnetic quantum number ‘ms’ determine?
The direction of spin and can values of +1/2 or - 1/2.
What is the aufbau principle?
Electrons fill orbitals in order of increasing energy.
What is Hund’s rule?
When degenerate orbitals are available, electrons fill each singly, keeping their spins parallel before spin pairing starts.
What is 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 subshell?
Degenerate.
What is the periodic tablet subdivided into?
Four blocks (s, p, d and f) corresponding to the outer electronic configurations of the elements within these blocks.
How can the variation in first, second and subsequent ionisation energies with increasing atomic number for the first 36 elements be explained?
In terms of the relative stability of different subshell electronic configurations. This provides evidence for these electronic configurations.
Anomalies in the trends of ionisation energies can be explained by considering the electronic configurations.
Where is there a special stability?
Associated with half-filled and full subshells. The more stable the electronic configuration, the higher the ionisation energy.
What can VSEPR (valence shell electron pair repulsion) theory be used for?
To predict the shapes of molecules and polyatomic ions.
How can 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.
What is the arrangement of electron pairs around a central atom?
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 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.
What is the electron pair repulsions decreasing in strength order?
non-bonding pair/non-bonding pair non-bonding pair/bonding pair bonding pair/bonding pair
