Physical Chemistry:
PC1 - Atomic structure:
Fundamental particles:
● Atoms are made up of protons, neutrons (the
nucleons), and electrons.
● Protons and neutrons are held together via a
strong nuclear force (stronger than
electrostatic).
● Electrons are found in shells.
Mass number, Atomic number and Isotopes:
● Number of protons is the atomic number (equal to the number of electrons in an ATOM)
and it defines the chemical properties (the element).
● Number of nucleons is the mass number, this can vary across atoms of the same element,
they are isotopes.
● An isotope is an atom with the same number of protons but a different number of
neutrons; they all have the same chemical properties due to the same electron
configuration.
The arrangement of electrons:
● John Dalton – plain solid
spheres.
● J.J. Thomson – must include
smaller –ve particles, electrons in
a sea of +ve charge.
● Rutherford –very thin gold foil
shot with 𝛂; most passed right
through and very little reflected.
● Bohr – an electron is actually a wave?? area of probability of electrons being there at a
given time.
● The number of max electrons on a shell is 2n²
,● Shorthand for electrons can be written as 2, 8, 18… (Na is 2, 8, 1)
The mass spectrometer:
● The relative atomic mass – the average mass of an atom of an element on a scale where
carbon-12 is exactly 12.
average mass of 1 atom
Relative atomic mass=
1
the mass of ¹² C
12
● Mass spectrometers can be used by forensic scientists to identify illegal substances.
● Steps of mass spectrometer:
1. Vacuum – kept under a high vacuum so ions don’t collide with any air
molecules and lose kinetic energy, interfering with results.
2. Ionisation – Electrospray is where a sample is dissolved in a volatile solvent
and forced through a fine hypodermic needle with a high voltage so sample
gains a H⁺ ion (M(g) + H⁺ → MH⁺(g)) and solvent evaporates to leave behind MH⁺
ions. Electron bombardment/impact is where a vapourised sample is shot by
an electron gun to fire high energy electrons to knock out, outer electron
forming a positive ion (M(g) → M⁺(g) + e⁻).
3. Acceleration – ions accelerated with an electric field, all with the same energy -
ions with more mass accelerate less and have a slower velocity than lighter
ions.
4. Ion drift – Ions fly in a tube towards a metal plate to be detected.
5. Detection – ions with same charge arrive at plate, light ones first, and flight
time is recorded. Ions pick up an electron and cause a current to flow.
6. Data analysis – mass spectrum produced as data is passed to the computer.
● Isotopes can be observed due to different masses so they have different flight times.
● Peak height is the relative abundance of each isotope in the given sample.
% of isotope × Mr of isotope
Relative atomicmass=
100
● The Mr of the elements in the periodic table is based on the % of isotopes on Earth.
More about electron arrangement in atoms:
● With the idea of quantum mechanics, there is an equation
that when solved gives the probability of an electron being in
a given volume.
,● The electron is no longer considered a particle but a cloud of negative energy.
● Different atomic orbitals have different energies, with the number telling us the main
energy level.
● The atomic orbitals of each main level have different shapes.
● The shape represents volumes where there is a 95% chance of having an electron there.
● First main energy level has 1 s-orbital; Second has 1 s and 3 p; Third has 1 s and 3 p all of
slightly higher energy; Fourth has 1 s and 3 p and 5 d.
● A single orbital can hold up 2 electrons.
● Electrons have opposite spins when 2 share an orbital.
● Atomic orbitals of lower energies are filled first.
Electron arrangement and ionisation energy:
● Ionisation energy (IE) is the energy needed to remove 1 mole of electrons from one mole
of atoms in gaseous state to produce one mole of +1 ions of the element in gaseous
state.
● More energy is needed to remove multiple electrons as the ion becomes more and more
positive (greater attraction).
● The group of an element can be determined from the ionisation energy - group = number
of IE before a BIIIIIGGGG jump.
PC2 - Amount of substance:
Ar and Mr, Avogadro’s constant and the mole:
1
● Scientists use carbon-12 as a baseline for relative atomic mass, of carbon-12 is exactly
12
1.
● Relative atom mass is the weighted average mass of an atom of an element, taking into
1
account isotopes, relative to of the Ar of an atom of carbon-12.
12
average mass of 1 atom
Relative atomic mass=
1
the mass of ¹² C
12
1
● Relative molecular mass is the mass of a molecule compared to of the Ar of an atom of
12
carbon-12.
, average mass of 1 molecule
Relative molecular mass=
1
themass of ¹²C
12
● Mr can be calculated by adding the Ar of all the atoms in the molecule.
● Relative formula mass is specific to ionic compounds as they don't exist as molecules.
● Avogadro constant is 6.022×1023 mol-1 – it defines the number of molecules/atoms in 1
mole of any substance.
mass , m( g)
number of moles , n=
Mr
Moles in a substance:
● Solutions are made up of a solute dissolved in a solvent.
● Units for concentration is mol dm-3 as it tells how many moles there are of the solute in 1
cubic decimetre of solution.
cm ³
● There are 1000cm3 in 1dm3 so conversion of cm3 to dm3 is: dm ³=
1000
moles
concentration(mol dm ⁻³)=
volume( dm ³)
Ideal gas equation:
1
● Boyle’s law: pressure , P ∝ and pressure , P × volume , V =constant
volume ,V
volume , V
● Charles’ law: volume , V ∝ temperature , T and =constant
temperature , T
pressure P
● Gay-Lussac’s law: pressure , P ∝temperature , T and =constant
temperature , T
pressure P × volume , V
● Combining these equation gives this: =constant for ¿ mass of gas
temperature ,T
● The ideal gas equation is then given as:
pressure ×volume=number of moles × gas constant ×temperature
P( Pa)V (m³)n R( J K ⁻ ¹ mol ⁻¹)T (K )
● The value of R is 8.31 J K-1 mol-1
● To convert Celsius, C to Kelvin, K, add 273.
Empirical and molecular formula:
● Empirical formula shows the simplest whole-number ratio of the atoms of each element in
a compound:
○ Find masses or percentages by mass of each element.
PC1 - Atomic structure:
Fundamental particles:
● Atoms are made up of protons, neutrons (the
nucleons), and electrons.
● Protons and neutrons are held together via a
strong nuclear force (stronger than
electrostatic).
● Electrons are found in shells.
Mass number, Atomic number and Isotopes:
● Number of protons is the atomic number (equal to the number of electrons in an ATOM)
and it defines the chemical properties (the element).
● Number of nucleons is the mass number, this can vary across atoms of the same element,
they are isotopes.
● An isotope is an atom with the same number of protons but a different number of
neutrons; they all have the same chemical properties due to the same electron
configuration.
The arrangement of electrons:
● John Dalton – plain solid
spheres.
● J.J. Thomson – must include
smaller –ve particles, electrons in
a sea of +ve charge.
● Rutherford –very thin gold foil
shot with 𝛂; most passed right
through and very little reflected.
● Bohr – an electron is actually a wave?? area of probability of electrons being there at a
given time.
● The number of max electrons on a shell is 2n²
,● Shorthand for electrons can be written as 2, 8, 18… (Na is 2, 8, 1)
The mass spectrometer:
● The relative atomic mass – the average mass of an atom of an element on a scale where
carbon-12 is exactly 12.
average mass of 1 atom
Relative atomic mass=
1
the mass of ¹² C
12
● Mass spectrometers can be used by forensic scientists to identify illegal substances.
● Steps of mass spectrometer:
1. Vacuum – kept under a high vacuum so ions don’t collide with any air
molecules and lose kinetic energy, interfering with results.
2. Ionisation – Electrospray is where a sample is dissolved in a volatile solvent
and forced through a fine hypodermic needle with a high voltage so sample
gains a H⁺ ion (M(g) + H⁺ → MH⁺(g)) and solvent evaporates to leave behind MH⁺
ions. Electron bombardment/impact is where a vapourised sample is shot by
an electron gun to fire high energy electrons to knock out, outer electron
forming a positive ion (M(g) → M⁺(g) + e⁻).
3. Acceleration – ions accelerated with an electric field, all with the same energy -
ions with more mass accelerate less and have a slower velocity than lighter
ions.
4. Ion drift – Ions fly in a tube towards a metal plate to be detected.
5. Detection – ions with same charge arrive at plate, light ones first, and flight
time is recorded. Ions pick up an electron and cause a current to flow.
6. Data analysis – mass spectrum produced as data is passed to the computer.
● Isotopes can be observed due to different masses so they have different flight times.
● Peak height is the relative abundance of each isotope in the given sample.
% of isotope × Mr of isotope
Relative atomicmass=
100
● The Mr of the elements in the periodic table is based on the % of isotopes on Earth.
More about electron arrangement in atoms:
● With the idea of quantum mechanics, there is an equation
that when solved gives the probability of an electron being in
a given volume.
,● The electron is no longer considered a particle but a cloud of negative energy.
● Different atomic orbitals have different energies, with the number telling us the main
energy level.
● The atomic orbitals of each main level have different shapes.
● The shape represents volumes where there is a 95% chance of having an electron there.
● First main energy level has 1 s-orbital; Second has 1 s and 3 p; Third has 1 s and 3 p all of
slightly higher energy; Fourth has 1 s and 3 p and 5 d.
● A single orbital can hold up 2 electrons.
● Electrons have opposite spins when 2 share an orbital.
● Atomic orbitals of lower energies are filled first.
Electron arrangement and ionisation energy:
● Ionisation energy (IE) is the energy needed to remove 1 mole of electrons from one mole
of atoms in gaseous state to produce one mole of +1 ions of the element in gaseous
state.
● More energy is needed to remove multiple electrons as the ion becomes more and more
positive (greater attraction).
● The group of an element can be determined from the ionisation energy - group = number
of IE before a BIIIIIGGGG jump.
PC2 - Amount of substance:
Ar and Mr, Avogadro’s constant and the mole:
1
● Scientists use carbon-12 as a baseline for relative atomic mass, of carbon-12 is exactly
12
1.
● Relative atom mass is the weighted average mass of an atom of an element, taking into
1
account isotopes, relative to of the Ar of an atom of carbon-12.
12
average mass of 1 atom
Relative atomic mass=
1
the mass of ¹² C
12
1
● Relative molecular mass is the mass of a molecule compared to of the Ar of an atom of
12
carbon-12.
, average mass of 1 molecule
Relative molecular mass=
1
themass of ¹²C
12
● Mr can be calculated by adding the Ar of all the atoms in the molecule.
● Relative formula mass is specific to ionic compounds as they don't exist as molecules.
● Avogadro constant is 6.022×1023 mol-1 – it defines the number of molecules/atoms in 1
mole of any substance.
mass , m( g)
number of moles , n=
Mr
Moles in a substance:
● Solutions are made up of a solute dissolved in a solvent.
● Units for concentration is mol dm-3 as it tells how many moles there are of the solute in 1
cubic decimetre of solution.
cm ³
● There are 1000cm3 in 1dm3 so conversion of cm3 to dm3 is: dm ³=
1000
moles
concentration(mol dm ⁻³)=
volume( dm ³)
Ideal gas equation:
1
● Boyle’s law: pressure , P ∝ and pressure , P × volume , V =constant
volume ,V
volume , V
● Charles’ law: volume , V ∝ temperature , T and =constant
temperature , T
pressure P
● Gay-Lussac’s law: pressure , P ∝temperature , T and =constant
temperature , T
pressure P × volume , V
● Combining these equation gives this: =constant for ¿ mass of gas
temperature ,T
● The ideal gas equation is then given as:
pressure ×volume=number of moles × gas constant ×temperature
P( Pa)V (m³)n R( J K ⁻ ¹ mol ⁻¹)T (K )
● The value of R is 8.31 J K-1 mol-1
● To convert Celsius, C to Kelvin, K, add 273.
Empirical and molecular formula:
● Empirical formula shows the simplest whole-number ratio of the atoms of each element in
a compound:
○ Find masses or percentages by mass of each element.
