Bonding Flashcards
What is the metallic bond
The electrostatic force of attraction between the positively charged ions and delocalised electrons.
Describe the structure of a metallic bond
a giant lattice of positively charged ions in a sea of delocalised electrons.
3 properties of a metallic bond
Electrical conductors
High mpts
Good thermal conductors
Metals going across the period trends and why
Conductivity increases as there are more delocalised electrons.
Metals going down a group trends and why
Mpts decrease as there are more occupied energy levels so the nucleus is further from the delocalised electrons.
What does a single covalent bond consist of
one shared pair of electrons
Define a pure covalent bond
when atoms of the same element form a covalent bond and the electrons are shared equally. This is because they have the same electronegativity.
Define a polar covalent bond
When atoms of different elements share electrons. Atoms with different electronegativity values will share the pair of bonding electrons unequally, forming partial changes or a permanent dipole.
In covalent bonds, what do the atom with the highest electronegativity do
will attract the bonding electrons closer towards it, therefore it turns slightly negative.
In covalent bonds what atom attracts the electrons (turns negative)
Highest electronegativity
Define the ionic bond
The ionic bond is the electrostatic attraction between positive and negative ions
Ionic bond structure
3D crystal lattice where oppositely charged ions surround each other.
What do elements far apart in the periodic table more likely to do
Form ionic rather than covalent bonds
4 properties of ionic bonds
Don’t conduct as solid ions are not free to move
High mpts
Conduct in molten or solution
Many are soluble
3 covalent networks
Boron
Carbon
Silicon
4 covalent network properties
High mpts
Hard substances
Don’t conduct
Insoluble
What state do van der Waals hold molecules
Liquid or solid
What atoms/molecules do vdw hold
Discrete atoms (noble gases)
Discrete molecules (diatomics)
Are VDW weak or strong
Weak
2 types of VDW
Permanent dipole - permanent dipole
London Dispersion Forces
What is LDF in monatomics
a force caused by an uneven distribution of the constantly moving electrons around the nucleus.
What does the uneven distribution of electrons do to monatomics
causes one side of the atom to have a temporary dipole.
What is a temporary dipole
a slightly + charge and one side a slightly - charge
Why do monatomics have low mpt/bpt
Their LDF are weak
How are LDF formed in covalent moleculars
formed as a result of electrostatic attractions between the temporary dipoles and induced dipoles caused by the movement of electrons
What is a polar covalent bond
a covalent bond in which the atoms have a difference in electronegativity.
What is a permanent dipole
the difference in charge in polar bonds
What forces of attraction between polar molecules
PD-PD
What does the spatial arrangement of polar covalent bonds do
sometimes result in the overall molecule becoming non polar.
Are hydrocarbons polar or nonpolar
Nonpolar
When does hydrogen bonding occur
Between very polar molecules
3 very polar molecules
F, N and O
What are hydrogen bonds
electrostatic forces of attraction between molecules that contain highly polar bonds.
What does a greater number of e/gfm mean for bpt and why
increases it as it makes a greater the chance of temporary and induced dipoles forming and therefore creating stronger LDF of attraction, so it requires more energy to separate the molecules.
Why sulfur has larger bpt than phosphorus
-Sulfur has an S8 discrete molecule structure and phosphorus has a P4 discrete molecule structure.
-The sulfur molecule contains more electrons than phosphorus, so there are more temporary dipoles in sulfur.
-This creates stronger LDF between the sulfur molecules, requiring more energy to separate them.
Fullerne/C60 mpt
280
Why would fullerene have a higher mpt than sulfur
it has more atoms present in the structure and therefore more LDF.
Why compare substances with similar electrons or gfms
because LDF are acting on all molecules, so same gfms/e means that the strength of the LDF will be similar. Means a bpt difference can be attributed to another type of van der Waal
Polar behaviour in electric fields
If a charged rod is held in a stream of liquid, the PD of polar liquids are attracted to the rod. (The flow changes)
Viscosity meaning
The resistance to flow
What molecules bonds are typically more viscous
polar or hydrogen bonds
Polar and nonpolar miscibility
Very polar molecules do not mix with nonpolar molecules
Explain polar and nonpolar immiscibility
The stronger hydrogen bonds between the water (polar) molecules cannot be broken by the nonpolar molecules as they have no charge to attract the polar molecules.
Ionic compounds and polar covalent compounds miscibility
tend to be soluble in polar solvents such as water.
Nonpolar molecular substances solubility
soluble in nonpolar substances.
If charge is evenly distributed the bonding is…
Nonpolar
If charge is unevenly distributed…
Polar
What type of bond/force is not a van der waal
Covalent
What type of bonds/forces are van der waals
Hydrogen
LDF
PD-PD
What does hydrogen bonding do to a compound
The presence of O-H or N-H bonds will increase the solubility of a compound.
Molecules with pd-pd polarity
Polar
Permanent dipole (describe and compare to H bonding)
Due to a difference in electronegativity between the atoms involved in a covalent bond. PD-PD interactions are weaker than hydrogen bonding.
