2.2 - Electrons, Bonding and Structure Flashcards
How many electrons are there in the 1st shell?
2
How many electrons are there in the 2ndshell?
8
How many electrons are there in the 3rdshell?
18
How many electrons are there in the 4thshell?
32
What is an orbital?
A region around the nucleus that can hold up to two electrons with opposite spins
How many orbitals does a s-sub-shell have?
1
How many orbitals does a p-sub-shell have?
3
How many orbitals does a d-sub-shell have?
5
What shape does a s-orbital have?
Spherical shape
What shape does a p-orbital have?
Dumbbell shape
What is the filling order for electron configuration?
1s^2 , 2s^2 , 2p^6 , 3s^2 , 3p^6 , 4s^2 , 3d^10 , 4p^6 , 5s^2 , 4d^10 , 6s^2 (You NEED to know up to 4p^6)
What are the rules for drawing electron configuration diagrams?
- Electrons fill orbitals with the same energy before pairing - Electrons will fill from the lowest available energy level - Two electrons can go into an orbital, providing that they are of opposite spin.
What must you be careful with when drawing/giving electron configurations of ions?
Adding and removing electrons Rule - If it is a positive ion, remove electrons, based on its charge. Say, it was a group 2 ion, remove 2 electrons (VICE VERSA for negative ions)
Define ionic bonding
The electrostatic attraction between oppositely charged ions
How does the ionic giant lattice come about?
Oppositely charged ions attract each other. Each ion attracts oppositely charged ions from ALL directions. Each of these in turn, ATTRACT MORE, oppositely charged ions. This forms a giant lattice structure.
How many ions are there in a giant ionic lattice?
Millions
Describe the melting and boiling points of ionic compounds?
The giant ionic lattice is held together b strong electrostatic forces. It takes a large amount of energy to overcome these forces. Therefore, their MP and BP are very high
Describe the solubility of ionic compounds
Ionic compounds tend to dissolve in water. This is because water molecules are polar. The water molecules are attached to the charge ions. They pull the ions away from the lattice making it dissolve.
Describe the electrical conductivity of ionic compouncs
Ionic compounds conduct electricity when they’re molten or dissolved but not when they’re solid. When solid - Ions are localised and cannot move about. Therefore, they cannot carry charge When molten/dissolved - Ions can conduct electricity as they are now mobile and can carry charge
Define covalent bonding
The strong electrostatic attraction betwen a shared pair of electrons and thenuclei of the bonded atoms.
When drawing covalent bonds, what rules must we follow?
- Don’t draw inner electrons - Only draw outer electrons
What is dative covalent bonding?
The electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms. In this type of covalent bonding, both electrons in the shared pair of electrons come from ONE PAIR.
What is meant by average bond enthalpy?
The amount of energy required to break a covalent bond?
The stronger the covalent bond, the higher the?
Average bond enthalpy
In Chemistry, do we prefer all bonds to be equally spread out as far as possible or the bonds being closer together so that repulsive forces are grater
We prefer all bonds to be equally spread out as far as possible (most energetically stable)
Give the bond angle of a compound with : 4 BP and 0LP
109.5
Give the bond angle of a compound with : 3BP + 1LP
107.0
Give the bond angle of a compound with : 2BP + 2LP
104.5
Give the bond angle of a compound with : 3BP + 0 LP
120
Give the bond angle of a compound with : 1BP +3LP
102.5
What is the bond angle of methane?
108.5 due to 4BPs
What is the bond angle of ammonia?
107.0 due to having 3BPs and 1LP
What is the bond angle of Water?
102.5
What is the shape, number of BPs, number of LPs and bond angle given to water?
Shape - Angular/Bent Number of BPs - 2 Number of LPs - 2 Bond Angle - 104.5
What is the shape, number of BPs, number of LPs and bond angle given to BF3?
Shape - Trigonal Planar Number of BPs - 3 Number of LPs - 0 Bond Angle - 120
What is the shape, number of BPs, number of LPs and bond angle given to Methane?
Shape - Tetrahedral Number of BPs - 4 Number of LPs - 0 Bond Angle - 109.5
What is the shape, number of BPs, number of LPs and bond angle given to PCl5?
Shape - Trigonal Pyrimadial Number of BPs - 3 Number of LPs - 1 Bond Angle - 107
What is the shape, number of BPs, number of LPs and bond angle given to SF6?
Shape - Octahedral Number of BPs - 6 Number of LPs - 0 Bond Angle - 90
Define electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond to itself
What is the most electronegative element?
Fluorine
What is the trend in electronegativity?
Increases: From left to right across a period in the periodic table Vertically up in groups
Explain the presence of a polar bond and permanent dipoles within molecules containing covalently bonded atoms with different electronegativities
In a covalent bond, the bonding electrons are pulled towards the more electronegative atom. This makes the bond POLAR. In a POLAR BOND, the difference in electronegativity between the two atoms causes a permanent dipole. The greater the difference in electronegativity, the more POLAR the bond.
Why are some molecules such as Cl2, CH4, and H2 non-polar?
No difference in electronegativity
What meant by a dipole?
A difference in electronegativity
Do polar molecules have permanent dipoles?
Yes, they do. The arrangement of polar bonds in a molecule determines whether or not the molecule will have an overall dipole.
In terms of symmetry and overall dipoles, if a molecule is symmetrical, is it polar or non-polar? Explain yourself
Non-polar… In symmetrical molecules, the dipoles cancel out. This means that the molecule has no overall dipole and is NON-polar.
In terms of symmetry and overall dipoles, if a molecule is asymmetrical, is it polar or non-polar? Explain yourself
Polar because… In asymmetrical molecules, the dipoles DO NOT cancel each other out. Therefore, the molecule has an overall dipole and is POLAR.
How can we work out if a molecule is polar or non-polar?
First, draw out the molecule in 3D. Now, label the partial charges on each atom Finally, look to see if they cancel each over out and there is an overall dipole
What are the 3 types of intermolecular force?
- Induced dipole dipole - Permanent dipole - dipole - Hydrogen bonding
How do induced dipole-dipole forces arise?
At any instant in time, it is possible that more electrons will lie to one side of the atom/molecules than the other. This forms an ‘instantaneous’ dipole. This induces a weak dipole in nearby atoms/molecules which creates weak forces between atoms/molecules.
How do induced dipole-dipole forces affect boiling/melting point?
Molecules with large surface area have higher boiling points. This is because, an increase in size (atomic radius) means that there are more induced dipole-dipole interactions and they are stronger. Therefore, more energy will be required to overcome the intermolecular forces. More induced dipole-dipoles = Higher MP/BP .
How do permanent dipole-dipole forces arise?
Polar molecules from permanent dipole-dipole interactions. The delta positive and delta negative charges on polar molecules causes weak electrostatic forces of attraction between molecules. These are called permanent dipole-dipole interactions.
Do permanent dipole-dipole forces arise in addition to induced-dipole- dipole forces or do they replace them completely?
They arise in ADDITION.
Why do molecules with permanent dipole-dipole interactions have a higher boiling point than molecules with just induced dipole-dipole interactions?
The extra attraction (caused by permanent dipole-dipole interactions) means that more energy must be put in the separate molecules.
Define Hydrogen bonding
The electrostatic attraction between two polar groups that occurs when a hydrogen atom, covalently bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine
What elements do H bonds only occur with?
NOF N - Nitrogen O - Oxygen F - Fluorine
List the unusual properties of water
- High surface tension and viscosity - Higher MP than expected - Ice floats on water
Explain the theory behind water’s unusual property of : High surface tension and viscosity
The strong H bonds need to be broken
Explain the theory behind water’s unusual property of : Higher MP than expected
The strong H bonds needs to be broken, which requires energy
Explain the theory behind water’s unusual property of: Ice floats on water
The long H bonds hold molecules apart in a lattice structure giving it a bigger volume than liquid water.
Explain the low melting point and low boiling point of simple covalent compounds
The intermolecular forces that hold together the molecules in simple covalent compounds are WEAK so don’t require much energy to break. SO, the MP and BP are normally LOW (they are often liquid or gasses at RT). However, as the number of intermolecular forces increase and/or as the intermolecular forces get stronger, MP and BP increase.
Explain why polar molecules are soluble in water
Water is a polar molecule so only tends to dissolve other polar substances. Compounds with H bonds such as NH3 or Ethanoic acid can form H bonds with water molecules, so will be soluble. Molecules that only have induced dipole-dipole forces, such as CH4 will be insoluble.
Explain why simple covalent compounds don’t conduct electricity
Even though some covalent molecules have permanent dipoles, overall, covalent molecules are unchanged. Therefore, they cannot conduct electricity.. Furthermore, localised electrons cannot carry charge.
