Bonding (Covalent) Flashcards
What is a covalent bond?
A shared pair of electrons between 2 atoms (usually 2 non metals?
How are covalent bonds represented?
By drawing lines from one atom to the other ( 1 line for each covalent bond)
What is the bond length?
When 2 nuclei are at a particular distance away from each other so that the attractive and repulsive forces are balanced. (Nuclei stay at a fixed position at that distance)
What si a dative covalent bond?
A type of covalent bond where the pair of electrons in the bond are supplied by one of the atoms
How are dative covalent bonds represented?
An arrow from the atom providing the pair of electrons to the atom receiving them
What 5 things are classed as a charge clouds?
How many charge clouds do they each represent?
Lone pair of electrons
Single covalent bond
Double covalent bond
Triple covalent bond
Dative covalent bond
All one charge cloud
What does the shape of covalently bonded species depend on?
The number of pairs of electrons and the number of lone pairs around the central atom
What is the relation between the number of lone pairs and the bond angle?
As the number of lone pairs increases the bond angle decreases because of their mutual repulsion
What is the electron repulsion theory?
The mutual repulsion is minimised when the pairs of electrons are as far apart as possible
What bonding pairs have the weakest to strongest repulsion?
Weakest is bonding with bonding
Middle is bonding with lone
Strongest is lone pair and lone pair
Why is the bond angle practically 120 degrees in molecules with 3 charge clouds where there are 2 bonding pairs and 1 lone pair?
There are 2 double covalent bonds so there is a stronger mutual repulsion so the lone pair can’t push them closer together
How do you calculate the number of charge clouds?
(Group number of central atom + number of bonds) + negative charge or - positive charges
Divided by 2
What is electronegativity?
The power of an atom to attract the pair of electrons in a covalent bond towards itself
Why is electron density not shared equally in covalent bonds?
The atoms have different electronegativities
What 2 factors affect electronegativity?
Nuclear charge
Size of the atom
How does nuclear charge affect electronegativity?
The higher the nuclear charge (number of protons) the higher the electronegativity as the atom is able Yk attract electrons more
How does the size of the atom affect electronegativity?
The smaller the atomic radius the higher the electronegativity because the electrons are closer to the nucleus so they are attracted to it more / stronger attraction
How does electronegativity change as you go down a group?
It decreases because
Atomic radius increases
Shielding increases (no effect)
How does electronegativity change as you go across a period?
It increases because
Atomic radius decreases
Nuclear charge increases
Shielding almost constant no effect
What is a polar bond?
An unequal distribution of the pair of electrons in a covalent bond
What is a dipole?
A difference in charge between 2 atoms caused by a shift in electron density in the bond between the atoms so polar bond
What is the relation between electronegativity difference and polarisation?
The higher the electronegativity difference the greater the polarisation
What are 2 conditions where you would have a non polar bond?
When the 2 atoms covalently bonded are the same so they have the same electronegativity
When the difference in electronegativity is less than 0.4
What is an asymmetrical molecule?
When the dipoles are not the same in different directions so they don’t cancel each other out which results in an overall permanent dipole moment
What is a symmetrical molecule?
When the dipoles are the same in all the different directions so they cancel each other out which results in no permanent dipole moment
What are 3 conditions for a symmetrical molecule?
No lone pairs
All atoms around central atom must be the same
All bonds around central atom must be the same ( eg all single covalent )
How do you predict bonding by looking at difference in electronegativity?
0% - covalent
25% - predominately covalent
50% - polar covalent
75% - predominantly ionic
100% - ionic
How do you calculate the % difference in electronegativity?
Difference in electronegativity divided by 3.3 multiplied by 100
When do you get Van Der Waals forces?
When the molecules are non polar (have the same electronegativity or less than 0.4)
Describe the van der waals attraction between forces
Since electrons are always moving the molecules create temporary dipoles which indices a dipole in neighbouring molecules (because of the slight charges)
What is the relation between van der waals forces and boiling points?
The more that there are or the stronger they are the higher the boiling points
What are 2 factors which increase the strength of van der waals forces?
How many electrons there are (more = stronger)
The size of the molecule ( large = more forces )
Why does a higher number of electrons increase the strength of can der waals forces?
It means that there is greater opportunities for and induced dipole to be seto up
Why do straight chain alkanes have stronger van der waals forces than branched alkanes?
They are packed closer together therefore it creates more points of contact between molecules which allowed for more dipoles to be indices resulting in more and stronger forces
When do permanent dipole dipole forces happen?
Only occurs in polar molecules (electronegativity difference is higher than 0.4 or is 0.4)
When do you get permanent dipole dipole forces and van der waals forces together?
When the polar molecule has an overall permanent dipole (asymmetrical)
Describe the attraction in permanent dipole dipole forces
The unequal distribution of charge is permanent as the more electronegative atom always has a higher share of electrons
What are the conditions for hydrogen bonding?
There must be hydrogen present
The hydrogen must be directly covalently bonded to either oxygen, fluorine or nitrogen
How do you draw a hydrogen bond?
A dotted line between the lone pair of electrons of the central molecule and the hydrogen with the delta plus charge
Define a permanent dipole dipole force
Electrostatic force of attraction between polar molecules
What are 2 properties of simple molecular substances?
Low melting and boiling point
Can’t conduct electricity
Why is water more dense than ice
In ice all the water molecules are hydrogen bonded and hydrogen bonds tend to be long so the h20 molecules are further apart
In water not all hydrogen bonded so close together which causes higher density
