Week Four Flashcards
ionisation energy
strength with an atom holds its electon in a indicator of chemical property
ionisation energy - more than 1 time
more energy is required for each time you remove an electron
zeff increase
number electron decrease
Ionisation energy trends
increases left to right
decreases down a group
Electron Affinity
energy change when atom accepts a proton to from ion
becomes more exothermic moving to right hand side
little change down group
Metallic CHaracter trends
increase down a group
decreases across a period
metals form
cations
Non metals form
anions
metal + metal
metal
Metal + non metal
ionic compound
Non metal + non metal
covalent
Metallic Bonds
in solid metals
bonded to several atoms
electrons are free to move which is why they have high electical conduction
Covalent Bonding
reduction in potential and kinetic energy
Eb
bond energy (between peak and midline)
Covalent bond drawing
a horizontal line between 2 atoms
unequal sharing of electrons
one atom has significantly higher nuclear charge
unsymmetrical distrubution
Electronegativity
abilityof atom to attract electrons
greater for non metals
Electronegativity trends
increases left to right
decreases down
ionic
more electrons so greater charge
Non polar covalent
similar electronegativites, shares electron equally
Polar covalent
One is more electronegative than the other so one has partially negative charged while other is partially positive
Polarity
determined by difference between electronegativity
Lone Pairs
not involved in bonding
Bonding pairs
valence electrons
Lewis Structures
valence electron arrangement
only outer shell interact
VSEPR
prediction of molecule geometry
Molecular Orbital Theory
describes the type of atomic orbitals used to share ore hold lone pairs
Octet rule
wants 8 electrons, gains, loses or shares
Formal charge
(number of valence electrons in free atom) - (number of non bonding valence electrons) - 1/2 (number of bonding electrons)
Electrostatic energy
2 charged species is proportional to magnitudes of charges and innversely proportional to distance between them
Coulomb’s law
E(electrostatic) - k(Q1Q2/r)
- describes potential energy of 1 pair of electrons
k
9.00 x 10^9
Q1 and Q2
charge of separate species
R
separation distance
electron - nuclei interactions
electrons and nuclei attract one another
attractions are energetically favourable
at lower energy than free electron
Electron - Electron interaction
repel
raises energy and reduces stability
Nuclei - Nuceli Interaction
repel
interactions reduce stability
Bond length trend
become longer as atom size increases
bond length
the separation distance at which a molecule has the maximum energetic advantage over the atoms
bond length - polarity
polarity contributtes because partical charges generate electrostatic attracion
bond length - multiple bonds
shorter than single bond
Bond energy
energy required to break bonds, multiply energy of single bonds by avogadros
bond energy - trend
increases as more electrons are shared
increases as electronegativity difference increases
decreases as bond gets longer
sigma bond
symmetric bond with respect to rotation around internucleas axis
Lattice energy
energy change on converting 1 mole of ionic solid into ions, depending on charges
Formal charge
charge atom would have if each its bonding electrons werre equally shared
VSEPR
minimising electron electron repulsion by placing electron pairs as far apart as possible,
two sets of electron pairs
linear
180*
three sets of electron pairs
trigonal planar
120*
Four sets of electron pairs
tetrahedral
109.5*
Five sets of electron pairs
trigonal bipyrimid
3 are positioned in corners of triangle 120* from one another and the 2 others are above and below centre atom at 90*
Six sets of electrons
octahedral
sit at 6 vertices of octahedron
90* and 180*
Dipole Moment
one end slightly postive one end slightly negative
Orbital overlap
when 2 orbitals of same phase are superimposed, results in new orbital
Hybrid orbitals
atomic orbitals obtained by combining 2 or more valence orbitals
- has to be 2 different energy levels
Molecular Orbital Thoery
overlap of 2 atomic orbitals leads to the formation of one bonding orbital and one antibonding orbital.
Inphase overlap
constructive and results in formation of molecular orbital with large amplitude and high electron density
Out of phase overlap
desctructive, gives molecular orbital zero amplitude and zero electron density
node
where amplitude changes
bond order
1/2 (number of electrons in bonding molecular orbitals - number of electrons in antibonding molecular orbitals)
Sp3 hybrid - shape
tetrahedral
sp2 hybrid - shape
Trigonal
Sp hybrid - shape
linear
