Molecular Shape & Bonding Flashcards
What are the characteristics of an ionic bond?
e- transferred
What are the characteristics of a covalent bond?
e- shared
What are the characteristics of a metallic bond?
e- pooled
Why do chemical bonds form?
They lower potential energy between charged particles that constitute atoms
What is pure covalent?
e- shared equally
What is polar covalent?
e- shared unequally
What is ionic bond?
e- transferred
Why does the metal lose e-?
Low ionisation energy of metals
Why does the non-metal gain e-?
Have high e- affinity
What is ions held together by?
Electrostatic attraction
What are the properties of ionic bonds?
Ionisation energy to form cation = endothermic
Acceptance of e- by non-metal = exothermic
Heat of formation for ionic compound = exothermic
Why is there energy differences in formation of ionic bond?
Forming crystal lattice
Is electrostatic attraction non-directional?
YES
What does it mean that electrostatic attraction is non-directional?
NO ionic molecule
= chemical formula = empirical formula = ratio of ions based on charge
What does Lewis Theory use?
Valence e-
Why are valence e- used in bonding?
Held most loosely
What do elements in the same column have the same properties?
Have same number of valence e-
What does Lewis Theory state?
e- are transferred from one atom to another atom = ions
What is the octet rule?
Rule of 8
Represents very stable configuration
How can represent valence e-?
Dot or crosses
What is the configuration?
1s2 2s2 2p6 3s2 3p6 3d10 4s2
What energy is required to remove e-?
Ionisation energy
What are elements with low ionisation energies?
Electropositive
What are elements that readily acquire e-?
Electronegative
What is group 1?
Alkali metals
What is group 2?
Alkali earth metals
What is group 3?
Al
What is group 7?
Halogens
What is group 6?
Chalcogens
What is group 5?
N + P
What are the properties of ionic compounds?
High melting points
Solid at RTP
Hard + brittle crystalline solids
Soluble in H2O
What happens if you have a larger ion?
Weaker attraction = lower lattice energy
What happens if you have a higher charge on ion?
Stronger attraction = higher lattice energy
What is Lewis Theory of covalent compounds?
Atoms achieve octet by sharing e-
A bond consists of a
shared pair of e-
What are e- called that are not shared?
Lewis Theory - covalent
Lone pairs
How is the shape of a molecule explained?
Electrostatic repulsion between bonding pairs + lone pairs
What pattern do atoms in the first period tend to follow?
C = 4 bonds + no L.P N = 3 bonds + 1 L.P O = 2 bonds + 2 L.P H = 1 bond + no L.P Halogens = 1 bond + 3 L.P
What is formal charge?
No. of valence e- - (no. of L.P + 1/2 no. of bonding e-)
What is it hen one atom has a single unpaired e-?
A free radical
What is Kekule structure?
Bonding e- drawn as lines + L.P not shown
What happens in covalent bonding of 2 different atoms?
Covalent bond where 2 e- are shared unequally
What do polar covalent bonds have?
Dipoles
Why is a bond polar?
When one atom is more electronegative than another atom
What is electronegativity?
The ability of an atom to pull bonding e- towards itself
What is the most electronegative element?
Fluorine
What is the least electronegative element?
Caesium
What is the electronegativity difference of purely covalent bond?
NONE
What is the electronegativity difference of non-polar covalent bond?
0.1-0.4
What is the electronegativity difference of polar covalent bond?
0.5-1.9
What is the size of the dipole indicated by?
Dipole moment
How do you calculate dipole moment?
Magnitude of charge on atom X distance between 2 charges
For complex molecules what does dipole moment depend on?
Dipole moments of all bonds in molecule + geometry of molecule
For molecules with only 1 covalent bond, what is the dipole moment?
Just dipole moment of that bond
What are the colours of electrostatic potential maps?
Blue > green > yellow > orange > red
Blue = most positive electrostatic potential
red = most negative electrostatic potential
Describe p-orbitals
Dumbbell shaped
Nodal plane that cuts dumbbell into 2 lobes
What do the +/- signs denote in the p-orbital?
Phase of lobe
NOT charge
How many degenerate (same charge) p-orbitals is there?
3
Symmetry around x, y + z axes
What are each of the p orbitals respective to the other two?
Perpendicular
What is the energy of 2p orbital compared to energy of 2s orbital?
Bigger
= farther away from nucleus
Why do atoms combine to form molecules?
Their total energy is lowered in the process
What are the 2 main theories to describe covalent bond?
Molecular orbital (MO) Valence-bond
What does MO involve?
Orbitals
BUT NOT atoms + bonds
In MO, what are molecules made up from?
Nuclei + e-
Nuclei are held together by molecular orbitals
What is MO?
e- distribution with e- density over the whole molecule
What is the only molecule that MO can be used to solve completely?
H2+
What is 1 rule for MO?
You must get the same number of MOs as starting AOs
What happens in an addition of wave functions?
MO
Bonding molecular orbital
What happens in subtraction of wave functions?
Anti-bonding molecular orbital
What does antibonding mean?
That it is a higher energy
What do bonding MO have?
High e- density on line between nuclei
How can 2p orbitals combine?
MO
Side on or end on
What does side on overlap lead to?
MO
Pi bonds
What is stronger a pi bond or sigma bond?
Sigma bond
What is the shape of 2 groups?
Linear
What is the shape of 3 groups?
Trigonal planar
What is the shape of 4 groups?
Tetrahedral
What is the bond angle for linear?
180 degrees
What is the bond angle for trigonal planar?
120 degrees
What is the bond angle for tetrahedral?
109.5 degrees
What is the hybridisation of linear (180 degrees)?
sp
What is the hybridisation of trigonal planar (120 degrees)?
sp2
What is the hybridisation of tetrahedral (109.5 degrees)?
sp3
