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