Chapter 6 - Shapes of Molecules and Intermolecular Forces Flashcards
What is the electron pair repulsion theory?
Electron pairs surrounding central atom determine molecule/on shape
Pairs repel each other so they are arranged as far apart as possible
Arrangement minimises repulsion, so holds atoms in definite shape
Different number of electron pairs -> different shape
How much degrees is the bond angle reduced by per lone pair?
2.5
What is the shape, diagram and bond angle in a shape with 2 bonded pairs and 2 lone pairs?
Non-linear
104.5
What is the shape, diagram and bond angle in a shape with 3 bonded pairs and 1 lone pairs?
Pyramidal
107
What is the shape, diagram and bond angle in a shape with 6 bonded pairs and 0 lone pairs?
Octahedral
90
What is the shape, diagram and bond angle in a shape with 5 bonded pairs and 0 lone pairs?
Trigonal bypramidal
90 and 120
What is the shape, diagram and bond angle in a shape with 4 bonded pairs and 0 lone pairs?
Tetrahedral
109.5
What is the shape, diagram and bond angle in a shape with 3 bonding pairs and 0 lone pairs?
Trigonal planar
120
What is the shape, diagram and bond angle in a shape with 2 bonded pairs and 0 lone pairs?
Linear
180
What is electronegativity?
Attraction of a bonded atom for the pair of electrons in a covalent bond
What is the Pauling scale?
A scale for measuring electronegativity
Increases upwards + across towards fluorine
If the electronegativity difference is large, what happens to the bond?
Becomes ionic rather than covalent
What is a non-polar bond?
Bonded electron pair shared equally between bonded atoms
Atoms same element, similar electronegativity
What is a polar covalent bond?
Bonded electron pair shared unequally
Different atoms with different electronegativity
What is a permanent dipole?
Dipole in a polar covalent bond which doesn’t change
What are intermolecular forces?
Weak interactions between dipoles of different molecules
What are induced dipole-dipole interactions (London forces) and how do they come about?
Exist between all molecules, only temporary
Movement electrons produce changing dipole in any molecule, at any instant an instantaneous dipole will exist but position shifts constantly
Instantaneous dipole will exist but shifts constantly
Instantaneous dipole induces a dipole on neighbouring molecule which induces dipoles on further molecules
More electrons in each molecule - larger instantaneous + induced dipoles - greater induced dipole-dipole interactions
What are permanent dipole-dipole interactions?
Act between permanent dipoles in polar molecules
Mean boiling point of polar molecules is much greater - as they have both London and permanent dipole-dipole interactions
Therefore extra energy needed to break additional permanent interactions, so boiling point is higher
What is a simple molecular substance?
Made of simple molecules
In solid state to form simple molecular lattices, held together by weak intermolecular forces, but within the molecules bonded strongly with covalent bonds
What are the physical properties of simple molecular substances?
Low melting/boiling point
Only weak intermolecular forces break
Not the strong covalent bonds
Do simple molecular structures conduct electrcitiy?
No mobile charged particles within structure
Where is hydrogen bonding found?
Found in molecules containing: electronegative atom w/ lone pair electrons (O,N,F) attached to a hydrogen atom
Explain why a solid less dense than a liquid
Solid is less dense as hydrogen bonds hold water molecules apart in open lattice structure, water molecules in ice father apart that in water
Therefore ice is less dense and floats
What are the properties of water?
Relatively high melting/boiling point
Hydrogen bonds and London forces - large quantity of energy is needed to break the hydrogen bonds
High surface tension + viscosity
