Chapter 6 Shapes of molecules and intermolecular forces Flashcards
What is the electron-pair repulsion theory?
- Electrons have negative charges and repel each other
- The electron pairs surrounding a central atom determine the shape of that molecule
- The electron pairs repel one another so that they are arranged as far apart as possible
- This arrangement minimises repulsion and holds the molecule in a definite shape
Why do lone pairs repel stronger than bonded pairs?
Lone pairs are slightly closer to the central atom
What shape has 4 bonding pairs and 0 lone pairs?
Tetrahedral
What shape has 3 bonding pairs and 1 lone pair?
Pyramidal
What shape has 2 bonding pairs and 2 lone pairs
Non-linear
What shape has 2 bonding pairs and 0 lone pairs?
Linear
What shape has 3 bonding pairs and 0 lone pairs?
Trigonal planar
What shape has 6 bonding pairs and 0 lone pairs
Octahedral
What is electronegativity?
The attraction of a bonded atom for the pair of electrons in a covalent bond
What electronegativity difference is considered to be a covalent bond
0 difference
What electronegativity difference is considered to be polar covalent
0 to 1.8
What electronegativity difference is considered to be an ionic bond?
greater than 1.8
When is a bond non-polar?
When the bonded atoms are the same or have similar electronegativity values
When is a bond polar?
When the bonded atoms have different electronegativity values
What is a dipole?
A separation of opposite charges
What are intermolecular forces?
Weak interactions between dipoles of different molecules
What are the three main categories of intermolecular forces?
- Induced dipole-dipole interactions (London forces)
- Permanent dipole-dipole interactions
- Hydrogen bonding
What are London forces?
Weak intermolecular forces that exist between all molecules, whether polar or non-polar.
How does induced dipoles occur?
- Movement of electrons produces a changing dipole in a molecule
- At any instant, an instantaneous dipole will exist
- That instantaneous dipole induces a dipole on a neighbouring molecule
- Which goes on to further induce dipoles on neighbouring molecules
What is a simple molecular lattice?
A lattice with molecules that are held in place by weak intermolecular forces
The atoms within each molecule are bonded together strongly by covalent bonds
What is the electrical conductivity of simple molecular substances?
There are no mobile charged particles in simple molecular structures, with no charged particles that can move, there is nothing to complete an electrical circuit therefore simple molecular substances cannot conduct electricity
What is the solubility of simple molecular substances?
-Non polar substances tend to be soluble in non-polar solvents
Why are non-polar simple molecular substances soluble in non-polar solvents?
- When a simple molecular compound is added to a non-polar solvent, intermolecular forces form between the molecules and the solvents
- The interactions weaken the intermolecular forces in the simple molecular lattice which cause the intermolecular forces to break and the compound dissolves
Where are hydrogen bonds found
Between Oxygen, Nitrogen or Fluorine
What are the two anomalous properties of water resulting from hydrogen bonds?
Ice is less dense than liquid
Water has a relatively high melting and boiling point
Why is ice less dense than liquid?
- Hydrogen bonds hold water molecules apart in an open lattice structure
- The water molecules in ice are further apart than in water
- Solid ice is less dense than liquid water and therefore floats
Why does water have a relatively high melting and boiling point?
- Hydrogen bonds are extra forces over the london forces
- More energy is required to break the hydrogen bonds in water
- Therefore, water has a higher boiling and melting point
