Periodicity Flashcards
Classical structure of electrons
It is a particle
quantum mechanics
is used to describe small particles such as electrons which have a wave-particle duality.
atoms and electrons are described as both
particle and waves
E
= hv
v
c / wavelength
quanta
a packet of energy or matter
electrons have
certain allowed energies
quantum number
label for allowed energy
where do the quantum numbers come from
Schrodinger equation
principal quantum number
describes the distance away from the nucleus and size of orbital
Azimuthal quantum number
the shape of the orbital and the angular momentum
magnetic quantum number
the orientation of the orbital
spin quantum number
the intrinsic angular momentum of an electron
Each orbital defined by an allowed value of
.
n, l and ml
what defines an allowed energy of an electron in an atom .
the first three quantum numbers
Hunds rule
this describes that in degenerate orbitals, electrons enter in seperate orbital before they start to fill in orbital with a second electron
pauli exclusion rule
electrons can have no more than 3 quantum numbers the same. it cannot have 4 quantum numbers the same
aufbau principle
electrons fill in by the lowest energy energy orbital first available. this is an exception with hydrogen
sp
two sp orbital. two p orbitals
sp2
three sp orbitals. one p orbital
sp3
4 sp4 orbitals
valence electrons feel less of the
positive nucleur charge
why do valence electrons feel less charge?
the core electrons cancel out some of the positive nuclear charge and shields the valence electrons
what is the effective nuclear charge?
it is the charge that the valenve electrons feel, this is calculated by subtracting the nuclear charge against the shielding constant
the effective nuclear charge
increases along period
the effective nuclear charge increases
down a group
ionisation energy
the is the energy it takes for isolated atoms the ground electrontric atate in the gaseous state to form 1+ gaseous ions
the ionisation energy increases
along the row. This is because the eefective nuclear charge increases and the atomic radii decreases
the ionisation energy in a group
decreases. although the atomic effective nuclear chrage increases the distance from the nucleus increases and the valence electrons are in a higher quantum shell
in a new row the ionisation energy
decreases. the valence electrons are in a higher quantum shell
what will cause a decrease
sharing orbital. Hunds rule. there will be a force of replusion
orbital types
going from s to p will cause a fall in ionisation energy
electronegativity
the ability for an atom to draw electron density towards itself within it being in a molecule
what are the general values for electronegativity?
betweenj 1-4
electronegativity
increases along the row but decreases down a group
electronegativity shows
if the bond will be ionic or covalent. the greater the difference in electrongetivity, the more likely it will be ionic bonding vice versa ,
what do atoms try and achieve by bonding
noble gas configuration
ionic bonding
electrons are formally transferred from one atom and the ions are held together by electrostatic interactions
covalent bonding
atoms share electrons
metallic bonding
sharing of free electrons among a structure of positively
charged ions (cations).
ionic bonding charcteristics
no directional restrictions
infinite 3D arrays
favors polaar subctances
high energy to break up interactions. so it has a high boiling and melting point
Ga
consists of covalently-bound pairs of atoms in both liquid
and solid state - these atomic pairs form with metallic
bonding between them.
covalent characteristics
directional. orbitals point at specific directions
forms both infinite and discrete arrays
prefers non polar substances
polarisability,
how easily an electron cloud is distorted by an
electric field
what impacts polarisability
charge and size of ion s
Size of the ion:
Smaller cation, and larger anion, give greater
covalent character.
The charge of cation:
Greater the charge of cation, greater is
the covalent character of the bond.
- Dative Bonding -
both electrons in a bond come from
one atom
Multicentre Bonding
- a pair of electrons is involved in
bonding between 3 or more atoms
Hydrogen Bonding
- polar molecules experience
attractive permanent dipole-dipole forces
Pi-stacking
- Attractive, non-covalent interactions
between aromatic rings
- Dispersive forces -
forces arising
from the interactions of instantaneous multipoles