Chem Qs

Explain why CF4 has a polar bond but does not have an overall dipole

Fluorine is more electronegative than carbon

It is a symmetrical tetrahedral and so the dipoles cancel out

Explain why the halogens show this trend in boiling point (Cl2,Br2,I2 - boiling point increasing )

Induced dipole dipole interactions (IDDI) between molecules increase and the number of electrons increase so more energy required to overcome the intermolecular forces

How IDDI forces arise

Electron distribution is unsymmetrical

Produces a temporary dipole in the molecule

Induces a temporary dipole between neighbouring molecules

IDDI exists between all molecules.Explain how these forces arise

The electron distribution in a molecule is unsymmetrical

This results in a temporary dipole in the molecule which in turn induces a temporary dipole between neighbouring molecules

Explain how permanent dipole dipole forces arise between HCl

Chlorine is more electronegative than hydrogen so a permanent dipole

The H (delta positive) in one molecule is attracted to the Cl (delta negative) in another molecule

Difference in MP & BP between simple covalent molecules

X has more electrons than Y

So had more stronger IDDI between molecules

That require more energy to overcome

Why is X a polar molecule but Y is not

X is an unsymmetrical molecule so the dipoles cancel out

Y is a symmetrical molecule so the dipoles do not cancel out

Why is X a s/p/d/f block element?

Because the highest energy electron is found in the s/p/d/f sub-shell

Describe & explain the two anomalous properties of water

Water has a higher melting/boiling point than expected as the strong hydrogen bonds holding the water molecules together require a lot of energy to overcome

The solid is less dense than the liquid as hydrogen bonding holds the molecules apart in an open lattice structure

Electrical Conductivity in an Ionic Substance

Can conduct electricity when molten but not when solid

When molten/in solution its ions are mobile but when in solid they are fixed in a lattice

Electrical Conductivity in a Metallic substance

Can conduct electricity when solid & molten as it had mobile (delocalised) electrons

Electrical Conductivity in a simple covalent substance

Cannot conduct electricity when solid or molten as it has no mobile charge carriers

Electrical conductivity in a giant covalent substance

Cannot conduct electricity when solid or molten as it had no mobile charge carriers

Water Solubility in a giant ionic substance

Can dissolve in water but is insoluble in organic solvents as it forms interaction with the polar water molecules

Water Solubility in a giant metallic substance

Does not dissolve in water as it does not form interactions with polar water molecules

Water solubility in a simple covalent substance

Does not dissolve in water but is soluble in organic solvents as it forms no interactions with the polar water molecules but does form interactions with organic solvents

Water solubility in a giant covalent substance

Does not dissolve in water as it does not form interaction with polar water molecules

Ionisation Energy -Explain the trend across period 2

Nuclear Charge Increases across the period

Outer electrons are in the same shell (atomic radius decreases)

Shielding is similar / same

Nuclear attraction increases

Electrons require more energy to be removed

So ionisation energy increases across the period

Explain why is there an increase in first ionisation energy between F & Ne

Ne has a greater nuclear charge than F

Outer electrons are in the same shell so shielding is similar/same

Nuclear attraction is greater in Ne than in F so ionisation is higher as it is harder to remove an electron

Explain the trend in first ionisation energy going down group 0

As you go down the group ionisation energy decreases

Nuclear charge increases, outer electrons are in shell further from the nucleus so shielding increases

Nuclear attraction decreases so electrons require less energy to be removed

Mg has a greater ionisation energy than Sr. Explain why. (Down a group )

Mg has a weaker nuclear charge

Mg has fewer shells so shielding is less

Nuclear attraction is greater in Mg than Sr Ionisation energy of Mg is greater

Therefore harder to remove an electron

Ionisation between period 1 & 2 (Be & B - Mg & Al)

Electron removed from Be/Mg is from S subshell

Electron removed from B/Al is from thr P subshell

P subshell is higher in energy than S subshell

Less energy required to remove an electron from Be/Mg

Ionisation decreases between N & O (3p3) or between P&S

A p orbital of O/S contains a pair of electrons which repel each other

Less energy is requited to remove the electron from O/S

Explain why the 2nd IE of O has a greater value than the 1st IE of Oxygen

The 2nd IE of Oxygen is greater than the first as the proton:electron ratio increases

So there is a greater nuclear attraction

State & Explain the trend in oxidising power down group 7

Nuclear charge increases - this is outweighed by more shielding therefore there is a weaker nuclear attraction so the ability to gain an electron decreases therefore it is weaker oxidising agent

Explain how the addition of cyclohexane would confirm the identity of the 3 halogens

Add solvent to each halide solution

Chlorine pale green - aqueous & organic layer

Bromine orange - aqueous & organic

Iodine - aqueous layers brown

organic layer purple

State any assumptions you have made in your calculation

Suggest improvements for obtaining a more accurate value for enthalpy change

Assumptions - no heat loss + c(SHC) is the same for solution 4.18 + complete reaction

Improvements - use a polystyrene cup + use a lid + more precise balance

Trend in alkalinity of Group 2 Hydroxides

Group 2 hydroxides are more soluble as you go down the group

Solution contains more concentratuon of OH- ions increases

pH increases and solution is more alkaline

Describe & explain the trend in reactivity of the group 2 elements with dilute HCl going down the group

Nuclear charge increases (atomic radius & shielding increases)

Nuclear attraction decreases

Ionisation energy decreases so it is easier

State & Explain the trend in alkalinity of the group 2 hydroxides

As you go down the group the solution is more alkaline so the pH increases

Group 2 hydroxides are more soluble as you go down the group

Solution contains more concentration of OH- ions increases

Explain the increase in boiling points of the cycloalkanes

More/stronger induced dipole dipole forces

More surface contact / More carbons

Why is there an increase in the boiling point of the alcohols as chain length increases

As the chain increases there are more electrons and more surface contact so stronger IDDI and so more energy required to overcome intermolecular forces

State two other methods that are used to process waste polymers

combustion for energy productuon

organic feedstock

production of plastics/other chemicals

Describe 2 differences between a sigma bonds and a pi bond

A sigma bond is between bonding atoms AND a pi bond is above and below the bonding atoms/nuclei.

A sigma bond has direct/head-on overlap of orbitals AND a pi bond has sideways overlap.

Reactivity of different haloalkanes

As we go from C-F → C-I the bond enthalpies decrease (bonds get weaker)

It becomes easier to break the C-halogen bond and therefore easier to lose the halide ion

The haloalkanes become more reactive

Where is the ozone layer found

Upper atmosphere

Formula for ozone

O3