1.4 Flashcards
What is a covalent bond?
A shared pair of electrons with opposed spins between two atoms
What is a co-ordinate bond?
covalent bond where both
electrons come from one of
the atoms
What is an ionic bond?
Formed by the electrostatic attractions between the cations and anions after one atom gives one or more electrons to the other
What is the name given to many ions together
Solid lattice
How is ionic bonding energetically possible
Although energy is needed to form the ions it is repaid by the strong electrical attraction between the cation and anion
Describe the attractive and repulsive forces within a covalent bond
Electrons in the pair repel each other
Overcome by their attractions to both nuclei
Describe how an ionic bond is structured due to attractive and repulsive forces
Ions are arranged so each cation is surrounded by many anions and vice versa
Maximises attraction
Minimises repulsion
What is electronegativity
The measure of the ability of an atom in a covalent bond to attract the electron bonding pair
How is bond polarity governed
Difference in electronegativity value
Most electronegative atoms
F O N
What is a dipole
Separation of charge in a molecule
One part is partially negative and another partially positive
How do dipoles arrange themselves
Negative region of one molecule is close to the positive region of another molecule so that there is a net attraction between them
What are Van der Waals forces
Weak intermolecular forces
2 types of van der waals forces
Dipole-dipole
Induced dipole-induced dipole
What is a hydrogen bond
a relatively strong intermolecular bond having a hydrogen atom joined to a very electronegative element in a molecule and bonding to another electronegative element in another molecule.
Why is hydrogen bonding stronger than that of van der Waals forces
Small hydrogen is sandwiched between 2 electronegative element which allows close approach
Which is longer in a diagram showing hydrogen bonding - the hydrogen bond or intramolecular bond?
Hydrogen
What shape is given to ice and why
Tetrahedral
Oxygen has 2 lone pairs and Hydrogen has 2 atoms
Describe the trend in boiling temperatures of intermolecular bonding
- increase with strength of forces
- VDW - steady increase with molecular mass and larger dipoles
- H bonds much higher boiling temperature than VDW of similar sized molecules
What is a bonding pair?
two electrons having opposed spins that bond two atoms in a molecule together by a covalent or co-ordinate
bond.
What is a lone pair?
two elections having opposed spins that belong to one atom only and are not involved in bonding to another atom
What are the principles of the VSEPR theory
- Shape of molecules are governed by the electron pairs around the central atom
- Electron pairs repel each other as far away as possible to minimise repulsion
- lp-lp>lp-bp>bp-bp
Name, angle and example of molecule with 2 electron pairs
Linear
180
BeCl2
Name, angle and example of molecule with 3 electron pairs
Trigonal planar
120
BF3
Name, angle and example of molecule with 4 bonding pairs
Tetrahedral
109.5
CH4
Name, angle and example of molecule with 5 electron pairs
Trigonal bipyramidal
90/120
PCl5
Name, angle and example of molecule with 6 electron pairs
Octahedral
90
SF6
Name and angle of molecule with 3 bonding pairs and 1 lone pair
Trigonal pyramidal
107
Name, angle and example of molecule with 2 bonding pairs and 2 lone pairs
Angular, bent
104.5
Water
What is a solute
The substance that dissolves in the solvent
What is a solvent
Liquid medium in which the solute dissolves
Commonly water
What is a saturated solution
One that cannot dissolve any more solute under the existing conditions
What is a polar molecule
Molecule with some separation of positive and negative charge
Does oil dissolve in water - why
No
Will form separate layers
Water - H bonding
Hydrocarbons- VDW
Why do alcohols dissolve in water providing the hydrocarbon chain is not too long
Hydrogen bonding is present in both molecules
Why does water dissolve inorganic salts eg NaCl
There is a strong interaction between the ions in the salt and the water dipoles
How does water dissolve a polar molecule
Oxygen regions of water molecules align themselves around the cations
Hydrogen regions of water align themselves around the anions
The attractions of these are enough to pull the ions from the solid lattice so that it dissolves
