Bonding And Structure Flashcards
What is a covalent bond
The electrostatic attraction between a shared pair of electrons and the positive nuclei of bonded atoms
What is the most important thing to remember when drawing dot cross diagrams
The number of electrons an atom needs to gain to complete its shell is the number of itself puts into bonding. For example, nitrogen needs to gain 3 electrons so you put 3 into bonding to get 3 back
What is a dative covalent bond
Where one of the atoms supplies both of the shared electrons to the covalent bond
What happens if a polyatomic ion is negatively charged
Then the extra electron gained MUST have come from elsewhere to make a net charge so you show that by using a different symbol
What is ionic bonding
The electrostatic attraction between oppositely charged ions
What does ionic bonding occur between
A metal and a non metal. For example sodium chloride.
What is the shape of molecules determined by
The number of bonding pairs and lone pairs they have
What shape and bond angle is represented if there are 2 bonding pairs and no lone pairs
A linear shape with a 180 degrees bond angle.
For example BeCl2
What shape and bond angle is represented if there are 3 bonding pairs and no lone pairs
A trigonal planar shape with a 120 degrees bond angle
For example BF3
What shape and bond angle is represented if there are 4 bonding pairs and no lone pairs
A tetrahedral shape with an 109.5 bond angle
For example CH4
What shape and bond angle is represented if there are 3 bonding pairs and 1 lone pair
A pyramidal shape with an 107 degrees bond angle
For example NH3
What shape and bond angle is represented if there are 2 bonding pairs and 2 lone pair
A non linear shape with an 104.5 bonding angle
For example H2O
What shape and bond angle is represented if there are 6 bonding pairs and 0 lone pair
An octahedral shape with a 90 degree bond angle
What exam technique do you use when your asked about the shape of the molecule
1) State the number of bonding pairs and lone pairs
2) State that electron pairs repel and that lone pairs repel more than bonding pairs
3) State the shape and the bond angle
What happens if there are double or triple bonds
You call them bonding regions not bonding pairs
What do you say if you are asked about the shape of ions
It is referring to a covalent compound that are as a whole charged. For example NH4 + is a covalent compound that overral has a single positve chargwe
What is electronegativity
The ability of an atom to attract a bonding pair of electrons in a covalent bond
Why does electronegativity increase as the group number increases
The atomic radius is smaller higher up a group
So there is a smaller distance between the positive nuclei and negative bonding pair of electrons
So there is a greater attraction of the bonding pair
Why does electronegativity increase across a period
There are the same number of shells for all elements across a period
BUT as you go across the period the nuclear charge increases
So there is a greater attraction on the bonding pair of electrons
What happens when different atoms are bonded to another
There is a difference in electronegativity
What happens with the more electronegative atom
It attracts the bonding pair of electrons more strongly and so is slightly negative as the shared electrons lie closer to it
What happens with the less electronegative atom
Attracts the bonding pair of electrons less strongly so is slightly positive as the shared electrons lie further away from it
What does the difference in electronegativity make it
It makes the bonds polar. More electronegative atom is delta - and the less electronegative atom is delta +
What are the exceptions to this rule
C-H bonds are non polar
Also bonds between identical atoms are not polar
What rules are there for a bond to be polar
Have polar bonds
Must be asymmetrical (have a positive and negative end to the molecule)
some symmetrical molecules could be non polar as the dipoles cancel out
For example is BF3 polar or non polar
Non polar because it may have polar bonds but it is symmetrical so the dipoles cancel out
Is NH3 polar or non polar
Polar because the molecule has polar bonds and is asymmetrical
What are the 3 types of intermoleculer forces
Permanent dipole dipole forces
Induced dipole dipole forces
Hydrogen bonding
What is a permanent dipole dipole interaction
A weak attractive force between permanent dipoles in neighboring polar molecules. The bigger the dipole the stronger the interaction
What is the difference between H-F and H-Cl interactions
Both are permanent dipole dipole interactions but there is a bigger difference in electronegativity in H-F and H-Cl so there are bigger dipoles so stronger Permanent dipole dipole interactions
What are induced dipole dipole forces
They act between all molecules whether polar or non polar. They are the weakest intermoleculer force
How are induced dipole dipole interactions made
Uneven distribution of electrons within each molecule which creates an instantaneous dipole
induces a dipole in neighboring molecules
What is the only factor that affects the strength of induced dipole dipole interactions
The number of electrons
What are you explaining if you have to explain the boiling points of molecules
The strength of the intermoleculer force (state the correct one and be specific)
How much energy is required to break them
For example why do the halogens show a trend in boiling points
Down the group the number of electrons increases which means there are stronger induced dipole dipole forces which require more energy to break
What are hydrogen bonding
A stronger permanent dipole dipole interaction between the hydrogen atom of one molecule and a lone pair of electrons on a highly electronegative atom on a different molecule
What is the information on hydrogen bonding
Only between polar molecules
H+ - O/N/F bonds
How do you draw a hydrogen bond
Dipoles drawn on both molecules
Lone pair drawn on the O/N/F molecules
Bond drawn from the lone pair to the H on the other molecule
What are the 2 anomalous properties of water
Relatively high boiling point because the stronger hydrogen bonds require more energy to break
Ice is less dense than water because water molecules are held further apart by hydrogen bonds in a lattice
How can you determine which intermoleculer force is which
If it doesnt have polar bonds it is induced dipole
If it has polar bonds and is symmetrical it is induced dipole dipole
If it has polar bonds and isnt symmetrical and isnt bonded to O/N/F to H with a lone pair it is Permenant dipole dipole
If it is polar is not symmetrical and is lone pair bonded to O/N/F then it is hydrogen bonds
What is the comparison and explanation of relative strength of forces
1) Initial decision- stronger forces (PDD IDD etc)
2)Pattern (Boiling point increases down the group)
3) Identify the forces between particles and say specific intermoleculer forces
4) Make a comparison of relative strength so more electrons are in Iodine so the stronger the interactions
5) Explain in terms of energy “therefore the forces require more energy to overcome”
How would you describe metallic bonding
A giant metallic lattice with strong metallic bonds between positive metal ions and a negative sea of delocalised electrons. The ions are arranged in a regular repeating arrangement
What does a giant metallic lattice mean
The attraction between the positve metal ions and the delocalised sea of electrons
Why do metals have high melting and boiling points
The strong electrostatic attraction between positive ions and the sea of delocalised electrons requires a lot of energy to break
For example how would you explain the difference in melting points for Al and Mg
Al has a greater ionic charge and more delocalised electrons so there is a stronger electrostatic attraction between positve ions and delocalised electrons which requires more energy to break
Why can metals conduct electricity
The delocalised electrons are free to move to carry the charge
How does metallic bonding differ from ionic bonding
Metallic bonds involve a delocalised sea of electrons but ionic bonds dont
How does metallic bonding differ from covalent bonding
electron pairs are shared between the 2 bonded atoms and are “locked” into these bonds in covalent bonding
Electrons are delocalised and are free to move in metallic bonding and covalent bonding isnt
Why does solid soidum chloride not conduct electricity but sodium does
SC has an ionic structure as it occurs between a metal and non metal with ionic bonds between oppositely charged ions so there are no species free to move to carry the charge
Wheras S is a metal so has a metallic structure which has metallic bonds between delocalised sea of electrons and positive ions. The delocalised electrons are free to move to carry the charge
What is a giant ionic lattice
It has a regular repeating arrangement of oppositely charged ions
Why would some diagrams be better
There are no gaps between ions in a giant ionic lattice
Why do ionic compounds have a high melting point
The ionic bonds between oppositely charged ions are very strong and require a lot of energy to overcome
Why can ionic compounds conduct electricity when molton or in aqueous solutions but not when solid
The giant ionic lattice consists of ionic bonds between oppositely charged ions
These are locked in place and arnt free to move to carry the charge when solid
However when molton or aqueous the ion are free to move to carry the charge so can therefore conduct electricity
Why is water only soluble in polar solvent
Polar solvent molecules break down the ions in the lattice structure
What happens to the ions when potassium chloride dissolves in water
The positively charged potassium ions move to the slightly negative oxygen
Th negatively charged chlorine ions move to the slightly positive hydrogen
Why do simple covalent molecules have a low melting/boiling point
Weak intermoleculer forces between molecules which require little energy to break
Why are simple covalent molecules soluble
non polar substance are soluble in non polar solvents like polar substances are soluble in polar solvents because induced dipole dipole interactions form between the solvent and molecule
Why do simple covalent molecules have good electrical conductivity
There are no charged particles present and they are free to move
What are examples of giant covalent molecules
Diamond
Graphite
Graphene
Silicone
Silicone dioxide
Why does graphite have a high melting an boiling point
They have strong covalent bonds between atoms which require as large amount of energy to overcome
What is the solubility of graphite
Not soluble in polar or non polar solvent
What is the electrical conductivity of graphite
It conducts electricity as its bonded to 3 carbon atoms so it has delocalsied electrons which are free to move between layers to carry the charge
Why is graphite soft
It contains weak induced dipole dipole interactions between layers so they can easily slide over one another
What are the similarites between graphite and graphene
3 covalent bonds per carbon atoms in BOTH graphite and graphene
What is the difference between graphite and graphene
graphene is a single layer with no induced dipole dipole interactions
What is the structure and bonding in diamond
Each carbon atom is bonded to 4 others and each atom has a tetrahedral shape with 109.5 bond angle
Why does diamond have a very high melting point
Strong covalent bond between atoms which requires a lot of energy to overcome
How does diamond not conduct electricity
There are no delocalised electrons in its structure because its bonded to 4 carbon atoms so it is free to move to carry the charge
What is diamonds solubility
It is insoluble to BOTH polar and non polar solvents
Why is diamond hard
There are only strong covalent bonds between atoms
What is graphite structure
Parallel layers of hexagonally arranged carbon atoms with weak induced dipole dipole interactions between layers
H
Y
