Many Electron Atoms And Periodic Trends Flashcards
What were Bohr’s postulates?
Electrons orbit the nucleus in distinct circular paths at certain distances
Each orbit/shell corresponds to a certain energy level n
Electrons can only gain and lose energy by jumping between shells (∆E=hv)
What is quantum number n?
The principal quantum number - shell number
n = radial nodes + angular nodes + 1
What is quantum number l?
Angular momentum quantum number - the shape of the orbital / number of angular nodes
L = 0 s orbital
L = 1 p orbital
L = 2 d orbital
What is quantum number ml?
Magnetic quantum number - gives direction of the orbital
ml runs from -l to +l in steps of 1
How many orbitals are there in any given shell?
n^2
How do you find the number of nodes an orbital has?
n - 1
What’s the Pauli exclusion principal?
It dictates that two electrons with the same spin cannot occupy the same orbital
What is the Aufbau principle?
Orbitals are filled from the lowest energy state orbital first
What is Hund’s rule?
In degenerate orbitals, orbitals will fill up with single electrons of parallel spin before they are paired up - spin-pairing costs energy
What do angular nodes have to do effective nuclear charge?
For a given shell, orbital with higher quantum number l have more angular nodes - thus penetrating the nucleus to a lesser extent and hence have higher energies.
E.g. 2p orbital has one angular node at the nucleus, experiencing a lesser effective nuclear charge than a 2s orbital and therefore is of higher energy
Define relative atomic mass Ar
Ar is defined as the ratio of the average mass of atoms of a chemical element to the atomic mass constant, which is a twelfth of the mass of an atom of carbon 12
What is Avogadro’s constant?
NA = 6.022 x 10^23 mol^-1
What are the general principles of atomic radius when going down a group or across a period?
Atomic radii increase down a group due to increasing number of shells
They decrease across a period as effective nuclear charge increases
Why does atomic size matter?
Because it determines the coordination sphere of an atom
Si can expand its coordination sphere whereas C cannot
Define ionisation energy
Ionisation energy is the minimum energy needed to remove an electron from a gaseous atom
Why is the first ionisation energy always endothermic?
Because it requires energy to remove an electron from a neutral atom
What’re the trends of ionisation energies across periods and down groups?
Ionisation energies decrease down groups to to increased shielding
However they increase across periods because of increase in nuclear charge - lack shielding
Why is Boron’s 1st IE less than Beryllium’s?
Because the electron in Boron’s 2p orbital is less tightly bound than Beryllium’s 2s electron
Why is Nitrogen’s 1st IE higher than Oxygen’s?
Because the nitrogen atom has a relatively stable half-filled p-shell, more stable than the spin paired electron in oxygen’s 2p orbital
Why are 2nd IE higher - and why is Li and Na so extreme?
2nd ionisation energies are higher because electrons are now being removed from a +vely charged ion
Li and Na are extremely high because electrons are now being stripped from core electrons
What is electron affinity?
EA is a measure for an atom to gain an electron
What is electron affinity defined as?
It’s defined as the negative of electron gain
EA = -EG
What happens to electron affinity going left to right cars a period?
EA increases because the energy of the vacant orbital decreases
1st electron gain energies can be exo or endothermic, what are 2nd EG energies?
ALWAYS endothermic
Define electron negativity
Electronegativity is defined as the power of an atom in a molecule to attract electron density to itself
