3 - Bonding Flashcards
What are the three types of strong chemical bonds?
Ionic, covalent and metallic.
What does ionic bonding occur between?
Metals and non-metals
Explain the conductivity of ionic compounds.
Do not conduct electricity when solid, as no free electrons. However they are able to conduct when molten.
Why are ionic compounds brittle?
They form a lattice of alternating positive and negative ions. Therefore when stuck, ions may be moved to cause contact between like-charged ions.
What state are ionic compounds at room temperature? (Think NaCl)
Solid
Where does covalent bonding occur?
Between a pair of non-metal atoms.
What is a covalent bond?
A shared pair of electrons between two non-metal atoms.
Why do covalent molecules have low melting points?
Between the molecules there are only weak intermolecular forces. The covalent bonds are strong, however they are between atoms within the individual molecules.
Explain the conductivity of covalent molecules.
The molecules are neutral overall, meaning there are no charged particles.
What is a co-ordinate bond?
It serves as a covalent bond, but one atom donates a pair of electrons (a lone pair) and the other (that is electron deficient) gives none.
What are the properties of a dative covalent bond?
Same strength and length as ordinary covalent bonds.
What is a co-ordinate bond also known as?
A dative covalent bond.
What is electronegativity?
The ability of an atom to attract electron density in a covalent bond, towards itself.
What does electronegativity depend on? (3)
Nuclear charge
Distance between nucleus and outer shell electrons
Shielding of nuclear charge by electrons in inner shells
What are the trends in electronegativity across the periodic table?
Increase across periods
Increase up groups
So higher electronegativity in the top right
What is a polar bond?
One in which the electron density is slightly towards one of the atoms, due to a difference in electro negativity. Partial charges.
Where does metallic bonding occur?
In metal elements.
Describe metallic bonding.
In a metal, outer shells of atoms merge. These electrons no longer associate with particular atoms so are ‘in a sea’ of delocalised electrons, which surrounds a lattice of positive ions.
Why are metals good conductors of both electricity and heat?
The delocalised electrons are able to move and also very vigorously vibrate, carrying energy.
Why are metals ductile (can be pulled into wires) and malleable (can be beaten into a shape)?
After a small distortion, each ion is still in the same environment so shape is maintained.
Why do metals have high melting and boiling points?
They have giant structures, and strong attraction between the metal ions and delocalised sea of electrons, making the atoms difficult to separate.
What are the three types of intermolecular forces? (In strength order)
van der Waals
dipole-dipole
hydrogen bonding
When do dipole-dipole forces form?
Between two molecules with permanent dipoles, they will attract.
The size of van Det Waals increases with what?
The number of electrons present, so larger molecules produce stronger van der Waals
What do hydrogen bonds form between?
A hydrogen atom bonded to a very electronegative atom, this makes the H strongly partially positive.
A very electronegative atom with a lone pair, which is attracted to the hydrogen in the other molecule.
Can form between H and O, N, F.
What happens when ice freezes?
Hydrogen bonds form between the molecules, which increase spacing and makes it less dense than water.
What evidence is there to show the strength of hydrogen bonds?
Period 2 Hydrides (group 4,5,6,7) have much higher boiling points than other periods.
Why is there no temperature change while changing states?
Any energy supplied is absorbed to weaken the forces between particles.
What are the four types of crystals?
Ionic crystals
Metallic crystals
Molecular crystals
Macromolecular
Why do molecular crystals have low boiling points?
The intermolecular forces are weak, covalent bonds only exist inside the individual molecules.
What is a macromolecular structure?
A giant structure all held together by covalent bonds, leading to a high melting temperature.
Give an example of an ionic crystal?
Sodium chloride, NaCl
