Molecular Shapes and Intermolecular Forces Flashcards
We're down to the molecular level, and its pretty cool stuff...
What is the VSEPR Theory, and explain it
- Electron pairs around a central atom will position themselfs as FAR APART as possible
Name examples for Linear , Trigonal Planar, Tetrahedral , Trigonal Bipyramidal
- Linear = CO2, BeCl2, BeH2
- Trigonal Planar = AlCl3, BCl3,
- Tetrahedral = CH4, P4
- Trigonal Bipyriamidal = PF5
State the 8 main molecular shapes and angles needed in chemistry…
- Linear = 180^
- Trigonal Planar = 120^
- Tetrahedral = 109.5^
- Trigonal Bipyramidal = 120^ and 90^
- Octahedral = 90^
- Non-Linear = 104.5^
- Pyramidal = 107^
- Square Planar = 90^
What is the difference between triple, double and single covalent bonds?
and REPULSION?!?!?!?
NO DIFFERENCE!
* These bonded regions will all bring about the exact same molecular shapes
* Keep in mind tht BONDED PAIRS STILL DO REPELL, BUT NOT AS MUCH AS LONE PAIRS
How can we draw ionically charged molecules as compared to normall molecules??
- IF +VE: make sure to TAKE AWAY ELECTRONS from central atom
- IF -VE: make sure to ADD ELECTRONS to the central atom…
use the common sense with positive and negatives in ions since GCSE..
What is Electronegativity?
- This is the ability for an atom to attract electron pairs towards its nucleus in a COVALENT BOND
Explain the 3 main factors contributing to Electronegativity
- Nuclear Charge = An increase will cause increased attraction between positive nucleus and negative shared electron pairs = increased electronegeativity
- Atomic Radius = An increase will cause increased distance from positive nucleas, weakening attraction = decreased electronegativity
What will occur during differences in electronegativity?
- This will be due to a shared pair of electron being attracted more by one atom than the other
What determines what kind of bond will be formed?
ionic, colavlent, polar colavent……….
- If eletronegativity difference IS LESS THAN 0.4, this makes a pure covalent bond
- if electrongeativity IS MORE THAN 0.4 AND LESS THAN 1.7, this makes a polar covalent bond
- IF MORE THAN 1.7, this makes an ionic bond
How can we represent electronegativity on a molecule?
- Arrowhead with a line points in direction of partial negative charges
What can we say about molecular symmetry?
- If dipoles occur in EQUALL AND OPPOSITE DIRECTIONS, this will cause DIPOLE CANCELLING = nonpolar molecule
- If not, there WILL be an overall PERMANENT DIPOLE, bieng a POLARISED MOLECULE
Therefore, a molecule may have POLAR COVALENT BONDS but overall be a NON POLAR MOLECULE due to SYMMETRY AND DIPOLE DIRECTION
What is a Dipole?
- This is a molecule with a separation of partial + and - charges!
Name the Enthalpies of the intermolecular forces in order……..
plus a lil sneaker bonding……
- Induced Dipole-Dipole = 10 kjmol-1
- Permanent Dipole-Dipole = 20 kjmol-1
- Hydrogen Bonding = 40 kjmol-1
4. COVALENT BOND = 150 to 500 kjmol-1
Explain the occurence of Induced D-D Interactions….
- Due to the RANDOM MOVEMENT OF ELECTRONS, this may cause an instantaneous dipole in and atom/molecule
- This will cause the neighbouring atom to also have an induced dipole (chain effect)
- The forces of attraction are known as LONDON FORCES
instantaneous = super-quick temporary moment
ALL ATOMS AND MOLECULES EXPERIENCE THIS
Explain the factors that affect Induced D-D Interactions..
- DISTRIBUTION OF ELECTRON AT ANY TIME, as more eletrons a a pole = greater induced london force
- NUMBER OF ELECTRONS, as more eletrons randomly moving = potential for greater induced dipole
Explain the occurence of Permanent D-D Interactions…
look at this area, you’ll be silly not to………
- Only be can be experienced with PERMANENT dipoles only
- When polar molecules interact via partial charges of one another, held via this intermolecular force
!!!!!!!!!!!!!!!!!polar molecules can experience BOTH INDUCED AND PERMANENT D-D INTERACTIONS, giving them the HIGHER MP/BP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Ok, so so what really are Van der Waal’s Forces
another wired name down here………
- They refer to both INDUCED and PERMANENT D-D Interactions
- This is an outdated term, and should never be used unless otherwise instructed
- HOWEVER, London Forces only refers to INDUCED interactions, not permanent
London Forces = Dispersion Forces
Explain the occurence of Hydrogen Bonding
VERY UNIQUE INDEED…….,…
- Only occurs under FON Elements, with lone pairs available
- Must be a Hydrogen Atom convieniently around to INTERACT with the FON elements
FON = Flourine, Oxygen, Nitrogen !
How can we represent a hydrogen bond in a drawing?
USE DOTTED LINES!
Why would Ice happen to float in water?
- When frozen, hydrogen bonds will slow and eventually stop moving
- They will freeze, arranged in an open lattice that has a lot of internal space
- An INCREASE in volume for SAME mass will mean decrease in density (and float…)
Why does water have to be odd with its MP/BP?
- Strong hydrogen bonds! = a lot of energy to break this intermolecular force! = high tempratures needed to do so!
* STRONG HYDROGEN BONDS ARE ALWAYS THE REASON FOR ANYTHING TO DO WITH WATER
What general structures of compounds do we get?
- Giant Ionic Lattices (NaCl, MgO)
- Giant Covalent Structures (Diamond, Graphite)
- Simple Molecular compounds (Cl2, F2)
Why is the hydrogen bonding weaker in ammonia than water?
btw there are 3 points to mention
- This is due to oxygen having greater electronegativity, more lone pairs, able to form more hydrogen bonds per molecule
- Hence, all these factors will mean that depsite both havin hydrogen bonds, ammonia remains a gas at ambient temprature
What is it meant by “weighted mean mass?”
- This is the average masses taking into account relative abundances of the isotopes!!!!!
Why would a simple molecular compound not carry electrical charge at all?
- Due to NO MOBILE CARRIERS able to carry ELECTRICAL CHARGE through the structre!!!!!
