Carol Dandira (Kiwi )
Email :
Conceptualised notes for CIE AS/A2 Chemistry
(9701) aka… Chem Stuff
Compiled By Carol M.S. Dandira
Contents
- Chemistry Terms and their Definitions - page 1
- Trends and Variations– page 31
- Factors and Effects– page 37
- Formulae and Stuff to Calculate– page 46
- Reactions and Equations– page 61– (organic chemistry also included in
depth)
- Colour Changes and Observations - page 91
- Diagrams - page 93
- Reaction Mechanisms - page 121
These notes are divided into concepts instead of topics. This is just to help you identify the concepts you are
struggling with thus tackle them. If you feel there is a mistake or there is something missing, let me know via
email. Use in conjunction with the syllabus. They are only organised by concept but in no particular order (not
grouped by topic within the sections). I went through the syllabus and made sure each syllabus point is
included. Good luck! (if you want to thank me, you can do that via email toooo!!!)
Chemistry Terms and their Definitions (and
explanations If necessary)
1. First ionisation energy
energy required to remove one mole of electrons from one mole of gaseous
atoms to form one mole of gaseous 1+ ions.
- When given subsequent ionisation energies for an element, you can
deduce the group by looking at where there is the biggest jump from one
ionisation energy to the next. If it’s for 4th to 5th, then the element is in group
4.
2. Isotope
Atoms of the same element with the same number of protons and electrons
but different number of neutrons and mass numbers
- Have the same chemical properties because if same electronic
configuration and same number of electrons
- Have different physical properties because of different mass thus different
density (density = mass/ volume)
1
,Carol Dandira (Kiwi )
Email :
3. Electronic configuration + explain the electronic configurations in terms
of energy of the electrons and inter-electron repulsion
Electronic configuration describes how electrons are arranged in atoms, and it's
governed by principles that relate to energy levels and repulsion between electrons.
1. Energy of Electrons
Electrons occupy orbitals arranged into shells (energy levels) and subshells (s, p, d, f). These are filled according
to increasing energy:
• The closer an electron is to the nucleus, the lower its energy (e.g., 1s < 2s < 2p < 3s, etc.).
• Electrons fill orbitals in a way that minimizes the atom's total energy.
Aufbau Principle (Building-Up Rule)
Electrons occupy the lowest available energy orbitals first before filling higher ones.
• Example:
Carbon (6 electrons): 1s² 2s² 2p²
Orbital Energy Overlaps
Due to energy overlaps, 4s is filled before 3d:
• 4s < 3d in energy (at first), so electrons enter 4s before 3d.
2. Inter-Electron Repulsion
Electrons are negatively charged and repel each other. This repulsion affects:
• Orbital energies
• Electron arrangements
a) Shielding (Screening) Effect
Electrons in inner shells shield outer electrons from the full attraction of the nucleus.
• This reduces the effective nuclear charge felt by outer electrons.
• Example: In sodium (Na), the 1s² 2s²2p⁶electrons shield the 3s¹ electron.
b) Electron-Electron Repulsion Within Orbitals
• In the same orbital, two electrons repel each other, increasing energy slightly.
2
,Carol Dandira (Kiwi )
Email :
• Hund’s Rule: Electrons occupy degenerate orbitals (orbitals with the same energy, like 2p_x, 2p_y, 2p_z)
singly before pairing up, to minimize repulsion.
3. Stability and Exceptions
Sometimes, electron configurations deviate from the predicted pattern to gain extra stability:
• Half-filled and fully filled d subshells are more stable.
• Example:
Chromium (Cr): [Ar] 4s¹3d⁵(not 4s² 3d⁴)
Copper (Cu): [Ar] 4s¹3d¹⁰(not 4s² 3d⁹)
• These configurations lower the atom’s energy despite not following the simple Aufbau order.
4. Unified atomic mass unit
One- twelfth of a carbon- 12 atom
5. Relative atomic mass
Weighted average mass of an atom relative to one-twelfth of a carbon-12
atom
6. Relative isotopic mass
Weighted average mass of an isotope relative to one-twelfth of a Carbon-12
atom
7. Relative molecular mass
Weighted average mass of a molecule of a compound or element relative to
one-twelfth of a Carbon-12 atom
8. Relative formula mass
Weighted average mass of one unit of a substance relative to one-twelfth of a
Carbon-12 atom
9. Mole
A mole is the amount of substance that contains exactly 6.022 * 1023
elementary entities (such as atoms, molecules, ions, or electrons).
10. Empirical formula
The simplest whole number ratio of atoms of each element in a compound
11. Molecular formula
The actual whole number ratio of atoms of each element in a compound
12. Electronegativity
The power of an atom to attract electrons to itself
3
, Carol Dandira (Kiwi )
Email :
13. Ionic bonding
electrostatic attraction between oppositely charged ions (positively charged
cations and negatively charged anions)
14. Metallic bonding
electrostatic attraction between positive metal ions and delocalised electrons
15. Covalent bonding
electrostatic attraction between the nuclei of two atoms and a shared pair of
electrons
Fact: in general, ionic, covalent and metallic bonding are stronger than
intermolecular forces
16. Bond energy
energy required to break one mole of a particular covalent bond in the
gaseous state
17. Bond length
internuclear distance of two covalently bonded atoms
18. Standard conditions
A set of predefined environmental parameters set in order to ensure
consistency and compatibility in scientific experiments
19. Enthalpy change
The change in heat energy of a substance during a chemical reaction
20. Le Chatelier’s principle
if a change is made to a system at dynamic equilibrium, the position of
equilibrium moves to minimise this change
21. Activation energy
minimum energy required for a collision to be effective
22. Effective collision
a collision between reactant particles that results in the formation of new
products
23. Hydrocarbon
a compound made up of C and H atoms only
24. Enthalpy change of atomisation
Heat change when one of a gaseous atom is formed from its elements in
standard state
25. Lattice energy
4
Email :
Conceptualised notes for CIE AS/A2 Chemistry
(9701) aka… Chem Stuff
Compiled By Carol M.S. Dandira
Contents
- Chemistry Terms and their Definitions - page 1
- Trends and Variations– page 31
- Factors and Effects– page 37
- Formulae and Stuff to Calculate– page 46
- Reactions and Equations– page 61– (organic chemistry also included in
depth)
- Colour Changes and Observations - page 91
- Diagrams - page 93
- Reaction Mechanisms - page 121
These notes are divided into concepts instead of topics. This is just to help you identify the concepts you are
struggling with thus tackle them. If you feel there is a mistake or there is something missing, let me know via
email. Use in conjunction with the syllabus. They are only organised by concept but in no particular order (not
grouped by topic within the sections). I went through the syllabus and made sure each syllabus point is
included. Good luck! (if you want to thank me, you can do that via email toooo!!!)
Chemistry Terms and their Definitions (and
explanations If necessary)
1. First ionisation energy
energy required to remove one mole of electrons from one mole of gaseous
atoms to form one mole of gaseous 1+ ions.
- When given subsequent ionisation energies for an element, you can
deduce the group by looking at where there is the biggest jump from one
ionisation energy to the next. If it’s for 4th to 5th, then the element is in group
4.
2. Isotope
Atoms of the same element with the same number of protons and electrons
but different number of neutrons and mass numbers
- Have the same chemical properties because if same electronic
configuration and same number of electrons
- Have different physical properties because of different mass thus different
density (density = mass/ volume)
1
,Carol Dandira (Kiwi )
Email :
3. Electronic configuration + explain the electronic configurations in terms
of energy of the electrons and inter-electron repulsion
Electronic configuration describes how electrons are arranged in atoms, and it's
governed by principles that relate to energy levels and repulsion between electrons.
1. Energy of Electrons
Electrons occupy orbitals arranged into shells (energy levels) and subshells (s, p, d, f). These are filled according
to increasing energy:
• The closer an electron is to the nucleus, the lower its energy (e.g., 1s < 2s < 2p < 3s, etc.).
• Electrons fill orbitals in a way that minimizes the atom's total energy.
Aufbau Principle (Building-Up Rule)
Electrons occupy the lowest available energy orbitals first before filling higher ones.
• Example:
Carbon (6 electrons): 1s² 2s² 2p²
Orbital Energy Overlaps
Due to energy overlaps, 4s is filled before 3d:
• 4s < 3d in energy (at first), so electrons enter 4s before 3d.
2. Inter-Electron Repulsion
Electrons are negatively charged and repel each other. This repulsion affects:
• Orbital energies
• Electron arrangements
a) Shielding (Screening) Effect
Electrons in inner shells shield outer electrons from the full attraction of the nucleus.
• This reduces the effective nuclear charge felt by outer electrons.
• Example: In sodium (Na), the 1s² 2s²2p⁶electrons shield the 3s¹ electron.
b) Electron-Electron Repulsion Within Orbitals
• In the same orbital, two electrons repel each other, increasing energy slightly.
2
,Carol Dandira (Kiwi )
Email :
• Hund’s Rule: Electrons occupy degenerate orbitals (orbitals with the same energy, like 2p_x, 2p_y, 2p_z)
singly before pairing up, to minimize repulsion.
3. Stability and Exceptions
Sometimes, electron configurations deviate from the predicted pattern to gain extra stability:
• Half-filled and fully filled d subshells are more stable.
• Example:
Chromium (Cr): [Ar] 4s¹3d⁵(not 4s² 3d⁴)
Copper (Cu): [Ar] 4s¹3d¹⁰(not 4s² 3d⁹)
• These configurations lower the atom’s energy despite not following the simple Aufbau order.
4. Unified atomic mass unit
One- twelfth of a carbon- 12 atom
5. Relative atomic mass
Weighted average mass of an atom relative to one-twelfth of a carbon-12
atom
6. Relative isotopic mass
Weighted average mass of an isotope relative to one-twelfth of a Carbon-12
atom
7. Relative molecular mass
Weighted average mass of a molecule of a compound or element relative to
one-twelfth of a Carbon-12 atom
8. Relative formula mass
Weighted average mass of one unit of a substance relative to one-twelfth of a
Carbon-12 atom
9. Mole
A mole is the amount of substance that contains exactly 6.022 * 1023
elementary entities (such as atoms, molecules, ions, or electrons).
10. Empirical formula
The simplest whole number ratio of atoms of each element in a compound
11. Molecular formula
The actual whole number ratio of atoms of each element in a compound
12. Electronegativity
The power of an atom to attract electrons to itself
3
, Carol Dandira (Kiwi )
Email :
13. Ionic bonding
electrostatic attraction between oppositely charged ions (positively charged
cations and negatively charged anions)
14. Metallic bonding
electrostatic attraction between positive metal ions and delocalised electrons
15. Covalent bonding
electrostatic attraction between the nuclei of two atoms and a shared pair of
electrons
Fact: in general, ionic, covalent and metallic bonding are stronger than
intermolecular forces
16. Bond energy
energy required to break one mole of a particular covalent bond in the
gaseous state
17. Bond length
internuclear distance of two covalently bonded atoms
18. Standard conditions
A set of predefined environmental parameters set in order to ensure
consistency and compatibility in scientific experiments
19. Enthalpy change
The change in heat energy of a substance during a chemical reaction
20. Le Chatelier’s principle
if a change is made to a system at dynamic equilibrium, the position of
equilibrium moves to minimise this change
21. Activation energy
minimum energy required for a collision to be effective
22. Effective collision
a collision between reactant particles that results in the formation of new
products
23. Hydrocarbon
a compound made up of C and H atoms only
24. Enthalpy change of atomisation
Heat change when one of a gaseous atom is formed from its elements in
standard state
25. Lattice energy
4
