The electrons and the quantum mechanical model Flashcards
electromagnetic radiation
consists of energy particles that move as waves of energy
planck’s constant
6.626 x 10^-34 m2 kg/s =Js
equations for electromagnetic radiation
c= vλ
E= hv = hc/λ
h= planck’s constant
electromagnetic spectrum
radiowaves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays
atomic spectrum
when light from a heated element passes through a prism, it separates into distinct lines of color separated by dark areas. each element has its unique atomic spectrum of distinct lines
what are the lines in an atomic spectrum are associated with
with the changes in the energies of the electrons
quantum
very specific levels where the energy of the electron is limited to
principal quantum number
energy levels
n=1, n=2, n=3
energy increases as the value of n increases and electrons are further away from the nucleus
distances decrease quadratically
when do electrons move to a higher energy level
when they absorb energy
how can you promote an electron to a higher energy level?
provide an amount of energy equal to the level difference
what happens when an electron falls back to a lower energy level?
light is emitted
what is the energy emitted or absorbed equal to
the difference between 2 energy levels
why cannot Bohr’s model be correct?
- electrons moving at a constant speed around the nucleus would emit energy and this does not happen
- electrons would progressively slow down and fall on the nucleus and this does not happen
particle-wave duality of subatomic particles
electrons can behave like a particle or a wave
the electron has a wavelength equal to:
λ= h/mv
uncertainty principle
we cannot know exactly the position and speed of an electron
why do we want to know where the electron is around an atom?
if the electron is closer to the nucleus it is less prone to share with other elements and thus its position can influence the atom’s reactivity: electrons with the same levels of energy will form more stable bonds
what does the wave function depend on?
on the number of electrons in the atom
what is the value of the square of the wave function ψ^2?
the probability of finding an electron in a specific region in space
what does the wave function depend on?
values of the wave function depend on 3 integer numbers: n,l,m
orbitals
volumes in space where we have a defined probability of finding an electron
energy of a hydrogen atom
E= -1/n^2 x 2.18 x 10^-18 J
the 4 quantum numbers
- principal quantum number
- angular momentum quantum number
- magnetic quantum number
- electron spin number
angular momentum quantum number
l
describes the shape of the regions where there is non-zero probability of finding an electron
eg. if n=3, l= 0,1,2
magnetic quantum number
m
specifies the orientation in space of the orbital
if n=3, m=-2,-1,0,1,2
electron spin number
s
+- 1/2
if an electron is placed in a mf its energy will be based on the direction it spins in
how many orbitals in a level
n^2
how many orbitals in a sublevel
2l + 1
l=0, l=1, l=2, l=3
l=0 s
l=1 p
l=2 d
l=3 f
what do wave functions contain
at least one node: the point where the wave function has a value of zero, and thus regions with a probability of finding the electron is zero
what happens as we go further up in energy
we will have more nodes
nodes are proportional to n: number of nodes n-1
level n=2
l can assume the value of 1, referred to as p orbital. m ca be equal to -1, 0, 1 so there are 3 p orbitals. A p orbital has 2 regions of high probability which gives a dumbshell shape
wave function
describes the probability of finding a particle
what does it mean if an orbital has a node?
it can have positive and negative phases: which important for chemical bonding
Pauli exclusion principle
- each orbital can hold a maximum of 2 electrons
- electrons in the same orbital repel each other (coulomb’s law)
- electrons in the same orbital must have their magnetic spins cancel
madelung- kleckovskij rule
atomic orbitals are filled in order of increasing n+l
why is E(s) < E(p) < E(d) < E(f)
- shielding: when an electron is further away from the nucleus, it feels a nuclear charge that is partially shielded by the inner electrons. it experiences a charge Z(eff)<Z
- penetration: when a higher level electron gets closer to the nucleus, it experiences a higher nuclear charge and its energy decreases
chromium configuration
[Ar] 4s1 3d5
copper configuration
[Ar] 4s1 3d10
lewis symbols
represent the valence electrons as dots placed on sides of the symbol of an element
describe how atomic size changes along a period and going down a group
atomic size increases going down a group but decreases going from left to right across a period
what determines the atomic size
by the atom’s atomic radius, the distance between the nucleus and the outermost electron-accessible orbital.
ionisation energy
the energy needed to remove one mole of the outermost electrons in the gaseous phase
describe how ionisation energy changes
as the distance from the nucleus to the valence electrons increases, the ionisation energy decreases.
ionisation energy decreases down a group as the distance between the nucleus and valence electrons increases.
ionisation energy increases as we move along a period as the number of protons strengths the attraction of the nucleus for the valence electrons
how can divalent cations be obtained?
from 2 subsequent ionisations
how does the first ionization energy compare to the second ionization energy?
the first one if smaller than the second one
electron affinity
the energy released by an element when it gains an electron
describe whether electron affinity is endothermic or exothermic
1st EA: endothermic
2nd EA: exothermic
describe how metallic character changes
as we go down a group metallic character increases because the valence electrons are easier to remove when they are further from the nucleus
as we go along a period metallic characteristics decrease as the number of protons increases which strengthens the attraction of the nucleus for the valence electrons and makes it more difficult to remove a valence electron.
