Bonding and structure Flashcards
Ionic bonding
The electrostatic attraction between oppositely charged ions
Ionic lattice
The oppositely charged ions attract each other and form a giant lattice in which each ion is surrounded by 6 oppositely charged ions. This gives ionic compounds great stability as the forces of attraction between the ions is very strong.
Why do ionic lattices have a high melting point?
A lot of energy is needed to overcome the strong electrostatic forces of attraction between the oppositely charged ions. Melting pint increases with increasing ionic charge.
Ionic compounds and solubility
The water molecules are attracted to the ions and surround the ions breaking it up.
Ionic compounds and electrical conductivity
They do not conduct electricity when solid as the ions are in a fixed position and there are o mobile charge carriers. When it is liquid the ionic lattice breaks down and the ions are free to move and carry the charge.
Covalent bonding
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Dative covalent bond
This is when a shared pair of electrons has been supplied by only one atom. For example in Ammonia the hydrogen has no electrons
Average bond enthalpy
A measurement of covalent bond strength, the larger the value the greater the strength.
Linear
2 bonded pairs, 180 degrees
Trigonal planar
3 bonded pairs, 120 degrees
Bent
2 bonded pairs, 1 lone pair, 119 degrees
Tetrahedral
4 bonded pairs, 109.5 degrees
Trigonal pyramidal
3 bonded pairs, 1 lone pair, 107 degrees
2 bonded pairs and 2 lone pairs
bent, 104.5 degrees
6 bonded pairs
Octahedral, 90 degrees
Why are molecules shaped the way they are
The electron pairs repel each other so that they are as far apart as possible. The arrangement of electron pairs minimalize repulsion and holds the atom in a definite shape. Also state the number of bonded pairs and lone pairs of electrons
Electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond, the higher the value on the pauling scale the more electronegative it is. It increases towards F on the periodic table, so top and to the right.
Polar bonds and permanent dipole
The molecule contains covalently bonded atoms with different electronegativity. The bonded electrons are not shared equally. A polar molecule contains polar bonds with dipoles that do not cancel due to their direction.
Types of intermolecular forces
London forces (induced dipole), permanent dipole and hydrogen bonding
London forces
Weak intermolecular forces that exist between all molecules, they act between induced dipoles
An induced dipole
Is caused by the movement of electrons which produces a changing dipole. At any moment an instantaneous dipole will exist due to the imbalance of electrons, this induces a dipole in a neighbouring molecule. These attract on another and there is a weak force of attraction between the 2 molecules. Induced dipoles are only temporary.
What affects London forces
Molecules with more electrons have more ways of arranging their outer shell electrons, in any one moment an imbalance in the arrangement of electrons can occur and an instantaneous dipole is established. The more electrons there are the more chance of an instantaneous dipole. When there is a greater surface area, for example straight chain alkanes, there is a greater surface area on which the IMF can form, so they will have a higher boiling point.
How London forces affect structure
In a solid state, simple molecular substances form a regular structure and are arranged in a regular lattice. The molecules are held in place by weak intermolecular forces and the atoms within each molecule are bonded together strongly by covalent bonds. The dipole is always in the same direction and they face the same way
Lone pair repulsion
Each lone pair reduces the bond angle by 2.5 degrees
Permanent dipole-dipole
Occurs between polar molecules, it is stronger then induced dipole interactions. It occurs in addition with induced dipole interactions.
Hydrogen bonding
Occurs in compounds that have a hydrogen atom attached to either oxygen, nitrogen or fluorine, which must have an available lone pair of electrons. It occurs in addition to permanent and induced dipole-dipole interactions. It is the strongest type of intermolecular force.
Why does H2O have such a high boiling point
Due to the hydrogen bonding
Why is ice less dense then water
the hydrogen bonding holds water apart in an open lattice structure. The H2O molecules in ice are further apart then in water so it is less dense.
Solubility of covalent substances in non polar solvents
When a simple molecular compound is added to a non-polar solvent, intermolecular forces form between the molecules and the solvent. These interactions weaken the intermolecular forces in the simple molecular lattice and the compound breaks down. So non polar substances are soluble in non-polar solvents.
Solubility of non polar substances in polar solvents
Non polar substances tend to be insoluble in polar solvents. This is because the intermolecular forces between the polar solvent is too strong to be broken up.
Polar substances solubility
They are soluble in polar solvents because they attract each other.
Covalent compounds conductivity
There are no mobile charged particles in a simple molecular substances. This means that there is nothing to move and carry the charge
Giant covalent
Many billions of atoms are held together by a network of covalent bonds to form a lattice. Silica, silicon, diamond, graphite, graphene, Buckminster fulerine and carbon nanotubes.
Giant covalent melting point
Giant covalent lattices have a high melting point because covalent bonds are strong. High temperatures are needed to provide the large quantity of energy needed to break the many strong covalent bonds. As there is a strong electrostatic force of attraction between the shared pair of electrons and the nucleus.
Giant covalent solubility
Insoluble as the covalent bonds holding the atoms in the lattice are too strong to be broken by the interactions with the solvent.
Giant covalent conductivity
In diamond and silicon all outer shell electrons are involved in covalent bonding so none are available for conducting electricity. Graphene and Graphite can as they have free electrons which can move and carry the charge.
Metallic bonding
The strong electrostatic forces of attraction between the positive lattice and the sea of delocalised electrons
Metal conductivity
Metals are able to conduct electricity as the electrons are free to move and carry the charge.
metal boiling point
High temperatures are needed to overcome the strong electrostatic forces of attraction between the positive lattice and the sea of delocalised electrons.
Boiling point of simple molecular substances
Low due to the weak intermolecular forces which are easily broken. It is higher if they have hydrogen bonding or are polar as this is a stronger type of intermolecular force the London forces. The boiling point is also higher when there are more electrons as it means the London forces are stronger. When talking about boiling point nether refer to covalent bonding
What metals have a higher melting point
Those with a higher charge as they have more delocalised electrons so there is a bigger electrostatic attraction between the positive lattice and the sea of delocalised electrons
Melting point of metals as you go down the group
Going down the group, the size of the cation increases and the charge remains constant. The charge density thus decreases and the attraction between the cations and the delocalized electrons also decreases. The melting points and hardness therefore decrease.
