C6 Shapes Of Molecules And Intermolecular Forces Flashcards
What are the 3 main types of chemical bonds
Ionic
Covalent
Metallic
Define ionic bonding
Electrostatic attraction between pos and neg ions
Give an example of a ironically bonded substance
NaCl
Define covalent bonding
Electrostatic attraction between a shared pair of electrons and the nuclei
Define metallic bonding
Electrostatic attraction between the pos metal ions and sea of delocalised electrons
Electrons in which shell are represented in dot and cross diagrams
The outer shell
Why does giant ionic lattices conduct electricity when liquid but not when solid
In solid state, ions are in fixed positions and thus cannot move.
When they’re in liquid state, ions are mobile and this can freely carry the charge
Giant ionic lattices have high or low MP and BP?
High MP & BP
Large amount of energy is required to overcome the electrostatic bonds
In what type of solvents do ionic lattices dissolve
Polar solvents
E.g. water
What are ionic compounds soluble in water
Water has polar bond
H atoms have delta pos charge and O atoms have delta neg charge
These charges are able to attract charged ions
What is it called when atoms are bonded by a single pair of shared electrons
Single bond
How many covalent bonds does C form
4
How many CBs does Oxygen form
2
What is a lone pair
Electrons in the outer shell that are not involved in the bonding
What is formed when atoms share 2 pairs of electrons
Double bond
What is formed when atoms share 3 pairs of electrons
Triple bond
What is average bond enthalpy
Measure of average energy needed to break the bond
What is a dative CB
A bond where both of the shared electrons are supplied by one atom
How are oxonium ions formed
Formed when acid is added to water, H3O+
What does expansion of the octet mean
When a bonded atom has more than 8 electrons in the outer shell
What are the types of covalent structure
Simple molecular lattice
Giant covalent lattice
Describe the bonding in simple molecular structures
Atoms within the same molecule are held by strong CBs and different molecules are held by weak IMFs
Why do simple molecular structures have low MP and BP
Small amount of energy is enough to overcome the IMFs
Can simple molecular structures conduct electricity
No
They are non conductors
Why do simple molecular structures not conduct electricity
Have no free charged particles to move around
Simple molecular structures dissolve in what type of solvent
Non polar solvents
Give examples of giant covalent structures
Diamond
Graphite
Silicon dioxide, SiO2
List some properties of giant covalent structures
High MP and BP
Non conductors of electricity, except graphite
Insoluble in polar and non polar solvents
How does graphite conduct electricity
Delocalised electrons present between the layers are able to move freely carrying the charge
Why do giant covalent structures have high MPs and BPs
Strong CBs within the molecules need to be broken which requires a lot of energy
What does the shape of a molecule depend on
Number of electron pairs in the outer shell
Number of these electrons which are bonded and lone pairs
What is the shape and bond angle in a shape with 2 BPs and 0 LPs
Linear
180*
What is the shape and bond angle in a shape with 3 BPs and 0 LPs
Trigonal planar
120*
What is the shape and bond angle in a shape with 4 BPs and 0 LPs
Tetrahedral
109.5*
What is the shape and bond angle in a shape with 5 BPs and 0 LPs
Trigonal bipyramid
90* and 120*
What is the shape and bond angle in a shape with 6 BPs and 0 LPs
Octahedral
90*
What is the shape and bond angle in a shape with 3 BPs and 1 LPs
Pyramidal
107*
What is the shape and bond angle in a shape with 2 BPs and 2 LPs
Non-linear
104.5*
By how many degrees does each lone pair reduce the bond angle
2.5*
Define electronegativity
The ability of an atom to attract the pair of electrons (the electron density) in a covalent bond
In which direction of the periodic table does electronegativity increase
Top right, towards fluorine
What does it mean when the bond is non-polar
The electrons in the bond are evenly distributed
What’s the most electronegative element
Fluorine
How is a polar bond formed
Bonding atoms have different electronegativities
Why is water polar, but CO2 is non-polar
CO2 is symmetrical molecule, so there’s no overall dipole
What’s meant by IMF
Attractive force between neighbouring molecules
What are the 2 types of IMFs
Hydrogen bonding
Van der Waals’ forces
What is the strongest type of IMF
Hydrogen bonding
What are the 2 interactions that can be referred as Van der Waals’ forces
Permanent dipole - induced dipole interaction
Permanent dipole - permanent dipole interaction
Describe permanent dipole -induced dipole interactions
When a molecule with a permanent dipole is close to other non-polar molecules it causes the non-polar molecule to become slightly polar leading to attraction
Describe permanence dipole- permanent dipole interactions
Some molecules with polar bonds have permanent dipoles —> forces of attraction between those dipoles and those of neighbouring molecules
Describe London forces
London forces are caused by random movements of electrons
This leads to instantaneous dipoles
Instantaneous dipole induces a dipole in nearby molecules
Induced dipoles attract one another
Are LFs greater in smaller or larger molecules
Larger due to more electrons
Does BP increase or decrease down the noble gas group? Why?
BP increases
As number of electrons increases and hence strength of LFs also increases
What conditions are needed for hydrogen bonding to occur
O-H, N-H or F-H bond
Lone pair of electrons on O, F, N because O, N and F are highly electronegative, H nucleus is left exposed
Strong force of attraction between H nucleus and lone pair of electrons on O, N, F
Why is ice less dense than liquid water
In ice, water molecules are arranged in an orderly pattern. It has an open lattice with hydrogen bonds
In water, the lattice is collapsed and the molecules are closer together
Why does water have a MP and BP higher than expected
Hydrogen bonds are stronger than other IMFs so extra strength is required to overcome the forces
