AS Physical Chemistry

Define ionisation energy

The energy required to remove a mole of electrons from a mole of atoms in the gaseous state and is measured in kJ mol^-1

First ionisation energy equation

X(g) -> X+(g) + e-

Second ionisation energy equation

X+(g) -> X2+(g) + e-

Third ionisation energy equation

X2+(g) -> X3+(g) + e-

What is the trend in ionisation energy as we move across a period?

Ionisation energy tends to increase as we move across a period, however in period 2, there are two cases where the first ionisation energy decreases

What are the orbitals?

s, p, d, f

What does the sample chamber contain

Isotopes of that element

What does 'ionisation' do

Converts atoms into positive ions which are attracted to a negatively charged plate

What does ionisation cause

Causes the ions to accelerate which increases kinetic energy of the ions

What happens once the ions have passed through the plate

They stop accelerating and drift down the chamber towards the detector

Ions drift down the chamber at ...

Different velocities - lighter move faster

What happens at the detector

Each ion + gains electrons - this transfer of electrons causes a current to flow

The time taken to move down the drift chamber is used to determine the ...

Mass of the isotope

The size of the current produced when each isotope hits the detector is used to determine the ...

Abundance of each isotope

Which isotope will produce a greater current

A more abundant isotope

Equations for mass spectrometry

- KE = 1/2mv2 and v=d/t

What is electron impact?

vapourised, electron gun

What is electrospray?

- dissolved in solvent, high voltage syringe

equation for electrospray

M + H+ -> [M-H]+

equation for electron impact

X + e- -> X+ + 2e-

what are the two types of ionisation?

electrospray and electron impact

what are the 3 steps in mass spec?

ionisation, acceleration and detection

what happens during acceleration?

pos ions attracted to negatively charged plate, pass through a hole in the middle creating a beam of the sample - ion drift

what will happen is the molecules are not ionised?

they wont be able to accelerate or produce a current

mass spec equation for comparing 2 particles

m/t2 = m/t2

how do you find the velocity of a single ion?

divide the mass by Avogadro's constant

Define atomic number

the number of protons in the nucleus of an atom

How do you calculate relative atomic mass?

RAM = (abundance % x mass) / 100

Define relative atomic mass

The weighted mean mass of an atom of an element compared with one twelfthof the mass of carbon-12

Define relative molecular mass

The mass of one molecule or compound compared with one twelfth of the mass of carbon-12

What is Avagadro's constant?

6.0221 x 10^23

What does Avagadro's constant tell us?

The number of atoms in one mole of any element. One mole of any element weighs the same in grams as it's atomic mass

Equation for moles?

Moles = mass (g) /Mr

Equation for concentration?

Concentration (mol/dm3) = moles (mol) / volume (dm3)

define relative atomic mass Ar

The weighted mean mass of an atom of an element compared with one twelfth of the mass of carbon-12

define formula mass Mr

The mass of one molecule or compound compared with one twelfth of the mass of carbon-12

Define molecular formula

the number of atoms of each element in a compound

Define empirical formula

The simplest whole ratio of atoms of each element in a compound

How do we find the molecular formula from the empirical formula?

1. find formula mass of empirical formula

2. divide Mr/formula mass

3. multiple all elements by answer in step 2

How do we find the empirical formula from the mass or % by mass?

1. divide each % by the Mr of the element

2. divide all answers by the smallest number to find ratio

3. round to make whole number ratios

carbonate ion

CO3 2-

chloride ion

Cl^-

nitrate ion

NO3-

sulphate ion

SO4 2-

hydroxide ion

OH-

silver ion

Ag+

Ammonia

NH3

Ammonium

NH4+

What is the ideal gas equation?

PV=nRT

kPa to Pa

x1000

dm3 to m3

/1000

cm3 to m3

/1000000

degrees Celsius to K

+273

K to degrees Celsius

-273

What is the value of the ideal gas constant

8.314Jmol-1K-1

What is the equation for gas volume dm3?

gas volume dm3 (at RTP) = moles x 24dm3 mol-1

The volume of 1 mole of any gas at room temperature and pressure is

24000cm3 or 24dm3

Define ionic bond

The strong electrostatic attraction between oppositely charged ions

What is the formula for aluminium chloride?

AlCl3

What is the formula for iron(II) oxide?

FeO

What is the formula for sodium sulfate?

Na2SO4

What is the formula for magnesium hydroxide?

Mg(OH)2

What is the formula for copper carbonate?

CuCO3

Why do ionic compounds have high melting points?

Strong electrostatic attraction between ions means a lot of energy is required to overcome them

Why do ionic compounds only conduct electricity when molten or in solution?

Ions must be free to move and carry a charge

Water is _____ so positive end will be _________ to and surround ________ ions and vice versa

polar, attracted, negative

Define covalent bond

the overlap of orbitals containing a shared pair of electrons

Define dative covalent bond (or co-ordinate bond)

Where the shared pair of electrons has been supplied by one of the atoms

What is metallic bonding?

the attraction between delocalised electrons and positive ions arranged in a lattice

What are the properties of metallic bonding?

- pos ions surrounded by 'sea' of delocalised electrons

- strong attraction between pos ions and electrons

- high mpt, almost all solids at rtp

- can conduct electricity

- malleable

What are the properties of a giant ionic lattice?

- strong electrostatic attraction between oppositely charged ions

- regular 3D arrangement of pos and neg ions

- conduct electricity when molten and in solution

- high mpt, always solid at rtp

What are the properties of a simple covalent structure?

- dont conduct electricity

- low mpts, gases and liquids at rtp

- isolated molecules with weak forces between molecules

- strong bonds between atoms, electrons are shared in pairs

What are the properties of a giant covalent structure?

- most dont conduct electricity (except graphite)

- strong bonds between atoms, electrons shared in pairs

- high mpt, always solid at rtp

- repeating 3D structure with strong bonds between atoms

Why are macromolecular covalent structures strong?

held together by lots of strong covalent bonds

Why do macromolecular covalent structures have high bpts?

lots of strong covalent bonds takes lots of energy to overcome

Why do graphite and graphene conduct electricity?

delocalised electrons carry a charge throughout the structure

What are the 3 main macromolecular covalent structures?

graphite, diamond and silicon dioxide

Why do simple molecular substances have low melting and boiling points?

They have weak intermolecular forces so very little energy is required to overcome them. The strong covalent bonds between atoms are not overcome however.

Why can giant metallic structures conduct electricity?

delocalised electrons free to carry charge throughout structure

Why are giant metallic structures malleable and ductile?

layers can slide over one another

What does the dashed line mean in the shapes of molecules?

going away from you

What does the wedge mean in the shapes of molecules?

coming towards you

What is the shape name for a compound with 2 bonding pairs/negative regions

linear - 180°

What is the shape name for a compound with 3 bonding pairs/negative regions

trigonal planer - 120°

What is the shape name for a compound with 4 bonding pairs/negative regions

tetrahedral - 109.5°

What is the shape name for a compound with 5 bonding pairs/negative regions

trigonal bipyramid - 120° and 90°

What is the shape name for a compound with 6 bonding pairs/negative regions

octohedral - 90°

A double bond in a dot cross diagram counts as___

one bonding pair/negative region

What is electron pair repulsion theory?

- pairs of electrons repel all other electron pairs

- these electron pairs will move as far away as possible to minimise repulsion

What do lone pairs do?

Lone pairs repel more than bonding pairs

How much do you decrease the angle by is there are lone pairs?

2.5°

What is the shape name for 3 bonding pairs and 1 lone pair?

pyramidal shape

What is the shape name for 2 bonding pairs and 2 lone pairs?

bent

What is the shape name for 5 bonding pairs and 1 lone pair?

square pyramidal

What is the shape name for 4 bonding pairs and 2 lone pair?

square planar

What is the shape name for 4 bonding pairs and 1 lone pair?

seesaw shape - based on trigonal bipyramid so 2 angles

What is the shape name for 3 bonding pairs and 2 lone pair?

T shaped - based on trigonal bipyramid so 2 angles

Define electronegativity

A measure of the attraction of an atom to a bonding pair of electrons in a covalent bond

Describe and explain the trend in electronegativity

- increases across a period due to more electrons so stronger attraction to nucleus

- decreases down a group due to larger atomic radii and shielding so less attraction to the nucleus

What is the electronegativity difference for a covalent bond

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