Bonding and Structure Flashcards
Define ionic bonding
The electrostatic attraction between a positive and negative ions. Holds together cations and anions in ionic compounds
Draw dot and cross diagrams of Na2O and Magnesium bromide
Draw it an look at p11 of study pack
Define covalent bonding
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Draw dot and cross diagrams of CO2 and PCl5
Look at p15 of stud pack
What is the octet rule
That elements tend to combine in a covalent compound with 8 electrons in their outer shell
What is a lone pair of electrons
A pair of electrons in the outer shell not used in bonding
Define dative covalent bond
A special type of bond formed from 2 electrons form the same atom e.g. NH4+ (NH3 + H+ –> NH4+)
Both electrons have been donated by one atom
Draw dot and cross diagram for NH4+ and H3O+
look at study pack p17
Define average bond enthalpy
It is the average enthalpy change which takes place when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species.
Measurement of bond strength
Define metallic bonding
The electrostatic attraction between positive metal ions and delocalised electrons.
Why do metals have high melting and boiling points
A lot of energy is needed to overcome the strong electrostatic attraction between the cations and electrons.
Why are metals good conductors of electricity
Solid- delocalised electrons are mobile so can carry charge
molten- delocalised electrons and the cations can move and carry charge
Why are metals insoluble in water or non-polar solvents
Because the strong electrostatic attraction between the positive metal ions and electrons is too strong so a lot of energy is needed to overcome it.
Which out of sodium, magnesium and aluminium is the best conductor of electricity
Aluminium- Has a charge of +3 so more delocalised electrons per metal ion, so has the best capacity to carry charge.
Define malleable and ductile
Malleable- can easily be bent in to different shapes
Ductile- can be drawn in to a wire
Which metals are present in stainless steel and brass
Stainless steel- Fe and Cr
Brass- Cu and Zn
How does an alloy make a metal harder
Because each metal is slightly different sizes so they can’t easily slide over each other which means they are harder.
Why do ionic compounds have high melting and boiling points
There is a strong electrostatic attraction between the +ve and -ve ions and a lot of energy is needed to overcome this.
Do ionic compounds conduct electricity when solid and molten
solid- no- ions aren’t mobile as are in fixed lattice arrangement so can’t carry charge
Molten/ dissolved in water- Ions aren’t in fixed positions in the lattice structure so can move around and carry charge.
Are ionic compounds soluble in water
Yes - often they have good solubility in water- water is polar so is attracted to the opposite charges in the compound- water molecules levers it out of it’s compound surrounding it by H2O molecules.
Why are ionic compounds brittle
If there is even the smallest movement of a layer the positive ions will be next to other positive ions. this causes repulsion causing the structure to break apart.
Giant covalent lattices- boiling points
High- There are strong covalent bonds which need to be broken which requires a lot of energy
Simple covalent molecules- boiling points
Low- There have very weak intermolecular forces which are easy to overcome, so not much energy is required.
Giant covalent lattice- Electrical conductor
No- there are no mobile electrons or any other charged particles which can carry charge.
Simple covalent molecules- Electrical conductor
No- there are no mobile electrons or any other charged particles which can carry charge.
Giant covalent lattice- Solubility in non-polar solvents
No- The strong covalent bonds that hold it together require too much energy to overcome
Simple covalent molecules- Solubility in non-polar solvents
Yes- Weak intermolecular forces are easy to break, so the solvent molecules form similar intermolecular bonds with molecules.
Draw structure of diamond
Draw it and check that each carbon atom is covalently bonded to 4 other carbon atoms. it is a tetrahedral shape
Draw structure of graphite
Check it p30 of study pack- two layers and weak forces between the layers
Diamond- Electrical conductor
No- Has no mobile electrons to carry charge
Graphite- Electrical conductor
Yes- Carbon only forms 3 bonds so each has a spare electron which become delocalised so can move abd carry charge
Diamond- hardness
Very hard- each carbon atom forms 4 bonds and forms a tetrahedral structure for each atom. Strong covalent bonds need much energy to break
Graphite- hardness
Soft- there are weak intermolecular forces between layers which can be easily broken and the layers slide over each other.
Define giant covalent lattices of atoms
It is a 3D structure of atoms which is bonded together by very strong covalent bonds.
VSEPR (Valence Shell Electron Pair Repulsion) Theory states
- Electron pairs around an atom will repel each other
- They will tend to get as far apart as possible
- Number and type of electron pairs determines the shape
- Lone pairs repel more strongly than bonded pairs (this affects bond angle) reduction of about 2.5 degrees per lone pair.
If a central atom has 2 bonding pairs and no lone pairs around it what shape and angle will it be?
Linear- 180 degrees
If a central atom has 3 bonding pairs and no lone pairs around it what shape and angle will it be?
Trigonal planar- 120 degrees
If a central atom has 4 bonding pairs and no lone pairs around it what shape and angle will it be?
Tetrahedral- 109.5 degrees
If a central atom has 3 bonding pairs and 1 lone pairs around it what shape and angle will it be?
Trigonal pyramidal- 107 degrees
If a central atom has 2 bonding pairs and 2 lone pairs around it what shape and angle will it be?
Non- linear - 104.5 degrees
If a central atom has 6 bonding pairs and no lone pairs around it what shape and angle will it be?
Octahedral- 90 degrees
Draw shape and state angle of: PH3 GeCl2 BF4- ion AsH3
PH3- trigonal pyramidal 107 degrees
GeCl2- non-linear- 117.5 degrees
BF4- ion- tetrahedral- 109.5 degrees
AsH3- Trigonal pyrimidal- 107 degrees
What are the types of Van der Waals forces that exist
induced dipole-dipole and permanent dipole-dipole
London forces description
Electrons are permanently moving
At any single instant their distribution in a molecule is not even.
This results in an instantaneous, temporary dipole.
This dipole induces dipoles in neighbouring molecules.
This leads to a small electrostatic attraction between the neighbouring charges in the dipoles.
This attraction between the molecules are London forces.
2 factors that affect the strength of London forces
- Number of electrons in a molecule- more electrons the stronger the force because there are greater fluctuations.
- Contact between molecules- only an issue with molecules with approx. same number of electrons.
Less branched molecules have a higher contact area so stronger London forces
Define electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond
Define permanent dipole
A small charge difference between different atoms in a molecule. It does not change across a bond.
If there is a difference in electronegativity between atoms in a compound then they have partial charges and permanent dipoles.
Define polar covalent bond
It’s a bond with a permanent dipole- contains partial negative and partial positive charges on the bonded atoms
Define polar molecule
A molecule that has an overall dipole taking into account all dipoles across bonds and the shape of molecules.
When are molecules with polar bonds not polar overall
When they are symmetrical
Decide whether BeCl2, SnCl4 and CH2Cl2 are polar
BeCl2- Linear so won’t be polar
SnCl4- Tetrahedral- symmetrical so dipoles cancel each other out so not polar
CH2Cl2- Tetrahedral- C-H bond isn’t polar so dipoles don’t cancel each other out - is polar
Define hydrogen bonding
A strong dipole-dipole attraction between an electron deficient hydrogen atom of -NH, -OH or -HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule.
Which of these molecules have hydrogen bonding:
H2S, CH3OH, PH3, NO2, CH3NH2, CH2=O
CH3OH and CH3NH2
the others can’t because they don’t have and N-H, F-H or O-H bonds
Describe the density of ice compared to water
Ice is less dense than water. For a given volume there are fewer molecules of H2O in ice than in water. The molecules of H2O in solid ice are less closely packed than in liquid water.
