Bonding Flashcards
Describe how ionic compounds form a giant ionic lattice
A huge number of ions are formed which arrange themselves into giant ionic lattices. Every ion in the lattice is attracted to every other oppositely charged ion by electrostatic forces of attraction.
Use the idea of the giant ionic lattice to explain the properties of ionic compounds
They have very high melting and boiling points because it takes a great deal of energy to overcome the strong electrostatic forces of attraction which can only be achieved at high temperatures.
Ionic compounds are soluble in polar solvents such as water. The water molecules surround the ions which can overcome the electrostatic attraction between the ions causing them to dissolve in polar solvents.
-if charges on the ions increase, solubility decreases due to the water molecules not being able to overcome the electrostatic forces of attraction.
They cannot conduct electricity when solid.
Describe what is meant by a covalent bond
A shared pair of electrons.
Describe what is meant by a coordinate bond
When an atom shares its lone pair with an electron deficient atom.
Determine the shapes of molecules
The shape of a molecule is determined by the electron pairs surrounding the central atom.
Tetrahedral - 109.5 degrees
Trigonal Bypyramid - 90 and 120 degrees
Octahedral - 90 degrees
Describe what is meant by electronegativity
Electronegativity is the ability of an atom to attract the pair of electrons in a covalent bond.
Fluorine has the highest electronegativity
As we move down a group, electronegativity decreases but as we move across a period it increases.
Describe the factors that affect the electronegativity of an element
The size of the positive charge on the nucleus - as we move across a period the number of protons in the nucleus increases so the attraction between the nucleus and the pair of electrons in a covalent bond increases.
The atomic radius - the smaller the atomic radius, the closer the bonding electrons will be to the nucleus.
Shielding - the greater the number of inner shells, the lower the electronegativity.
Describe how a bond or molecule can be polar
A bond or molecule can be polar due to differences in electronegativity between atoms and the molecular geometry that determines whether the dipoles cancel out or reinforce each other.
-A bond is polar when N, O, F, Cl, Br, I atoms bond to a different atom.
-A molecule is polar if its asymmetric as the bond dipoles don’t cancel.
Describe what is meant by an intermolecular force
Intermolecular forces are the attractive forces that occur between molecules.
The 3 types of intermolecular forces are:
-Van Der Waals’ forces
-Permanent dipole-dipole forces
-Hydrogen bonds
Describe Van Der Waals’ forces
Caused by the movement of electrons in an atom which unbalances the charge distribution within the molecule.
-If electrons in one atom move to the right, they create an instantaneous dipole across the molecule which is constantly forming and disappearing.
-This causes the electrons in the 2nd atom to repel to the other side, creating an induced dipole which results in weak forces of attraction between molecules (S- and S+).
As the Mr of molecules increase, the number of electrons also increase which causes the boiling points of the molecules to increase so the VDW forces are getting stronger as Mr rises.
-VDW forces are present between all molecules but they are the only forces present between non polar molecules.
Describe permanent dipole-dipole forces
They occur between polar molecules only and occur in addition to VDW forces, the S+ end of one molecule is attracted to the S- end of a neighbouring molecule.
Describe what is meant by hydrogen bonding (strongest intermolecular force)
Occurs between molecules which contain a hydrogen atom bonded to either F, O or N (the 3 most electronegative atoms).
-A hydrogen bond is formed between a S+ Hydrogen atom in one molecule and a lone pair of electrons on a N, O or F atom in a neighbouring molecule.
When drawing H bonds you must show:
-2 molecules
-All lone pairs
-Partial charges (S+ and S-)
-The correct alignment of atoms
