CIE iGCSE Co-ordinated Sciences-C2.2 Atomic structure and the Periodic Table- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C2.2 Atomic structure and the Periodic Table – Study Notes
CIE iGCSE Co-ordinated Sciences-C2.2 Atomic structure and the Periodic Table – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe the structure of the atom as a central nucleus containing neutrons and protons, surrounded by electrons in shells
- State the relative charges and relative masses of a proton, a neutron and an electron
- Define proton number / atomic number as the number of protons in the nucleus of an atom
- Define mass number / nucleon number as the total number of protons and neutrons in the nucleus of an atom
- Determine the electronic configuration of elements with proton number 1 to 20, e.g. 2,8,3
- State that:
(a) Group VIII noble gases have a full outer shell
(b) the number of outer-shell electrons is equal to the group number in Groups I to VII
(c) the number of occupied electron shells is equal to the period number
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Structure of the Atom
An atom is the smallest particle of an element that can exist and still have the properties of that element. Atoms are made up of three main subatomic particles: protons, neutrons, and electrons.
Basic Structure:
- At the centre of the atom is the nucleus.
- The nucleus contains two types of particles:
- Protons – positively charged particles.
- Neutrons – neutral particles (no charge).
- Electrons move around the nucleus in regions called shells or energy levels.
\(\text{Atom} = \text{Nucleus (protons + neutrons)} + \text{Electrons in shells}\)
Key Features of Atomic Structure:
- The nucleus is very small but contains most of the atom’s mass.
- The electrons move very fast around the nucleus in fixed energy levels or shells.
- An atom is electrically neutral because the number of protons = electrons.
- Protons and neutrons have similar masses, while electrons are much lighter.
Example :
Describe the structure of a carbon atom in terms of its subatomic particles.
▶️ Answer/Explanation
Step 1: Carbon has atomic number 6 → 6 protons and 6 electrons.
Step 2: Mass number ≈ 12 → 6 neutrons.
Step 3: Electron arrangement = 2, 4.
Final Answer: A carbon atom has a nucleus containing 6 protons and 6 neutrons, surrounded by 6 electrons in two shells: 2 in the first and 4 in the second.
Relative Charges and Masses of Subatomic Particles
Atoms are made up of protons, neutrons, and electrons. These particles differ in charge and mass, which determines how they behave in an atom.
Relative Charge and Relative Mass
| Subatomic Particle | Symbol | Relative Charge | Relative Mass | Location in Atom |
|---|---|---|---|---|
| Proton | p⁺ | +1 | 1 | In the nucleus |
| Neutron | n⁰ | 0 (neutral) | 1 | In the nucleus |
| Electron | e⁻ | –1 | 1/1836 (≈ 0) | In shells around nucleus |
Explanation:
- Protons have a positive charge and give the atom its identity (atomic number = number of protons).
- Neutrons have no charge and add mass to the atom; they help stabilize the nucleus.
- Electrons are negatively charged and orbit the nucleus in shells; they balance the positive charge of the protons.
Comparison of Charge and Mass:
- The proton and neutron have similar masses (1 unit each).
- The electron has a very small mass (1/1836 of a proton) — almost negligible.
- In a neutral atom, the number of protons = electrons, so the overall charge is zero.
\(\mathrm{Total \ positive \ charge = Total \ negative \ charge}\)
Key Facts to Remember:
- Proton: +1 charge, mass = 1, inside nucleus.
- Neutron: 0 charge, mass = 1, inside nucleus.
- Electron: –1 charge, mass ≈ 0, in shells around nucleus.
Example :
State the relative charge and relative mass of a proton, a neutron, and an electron.
▶️ Answer/Explanation
- Proton: charge = +1, mass = 1
- Neutron: charge = 0, mass = 1
- Electron: charge = –1, mass = 1/1836
Explanation: Protons and neutrons are found in the nucleus and are heavy compared to electrons, which are light and found in shells around the nucleus.
Proton Number / Atomic Number
The proton number (also called the atomic number) is the number of protons in the nucleus of an atom. It is represented by the symbol Z.
Key Points:
- The proton number determines which element the atom belongs to.
- Each element has a unique number of protons — no two elements share the same proton number.
- In a neutral atom, the number of protons = number of electrons.
\(\mathrm{Proton \ number = Number \ of \ protons = Number \ of \ electrons \ (in \ a \ neutral \ atom)}\)
Example – Hydrogen:
- Hydrogen has 1 proton in its nucleus.
- So its proton number (atomic number) = 1.
- It also has 1 electron orbiting the nucleus.
\(\mathrm{Hydrogen: \ Z = 1}\)
How Proton Number Appears in Nuclear Notation:
\(\mathrm{^{A}_{Z}X}\)
- \( \mathrm{X} \) = chemical symbol of the element.
- \( \mathrm{Z} \) = proton (atomic) number = number of protons.
- \( \mathrm{A} \) = nucleon (mass) number = total number of protons + neutrons.
Example:
\(\mathrm{^{12}_{6}C}\)
- \( \mathrm{Z = 6} \) → 6 protons.
- \( \mathrm{A = 12} \) → total of 12 protons and neutrons.
- \( \mathrm{Neutrons = A – Z = 12 – 6 = 6}\).
Proton Numbers of Common Elements
| Element | Symbol | Proton Number (Z) |
|---|---|---|
| Hydrogen | H | 1 |
| Helium | He | 2 |
| Carbon | C | 6 |
| Oxygen | O | 8 |
| Sodium | Na | 11 |
Example :
State the proton number of oxygen and explain what it represents.
▶️ Answer/Explanation
Step 1: The proton number (atomic number) of oxygen is 8.
Step 2: This means an oxygen atom has 8 protons in its nucleus.
Step 3: In a neutral oxygen atom, it also has 8 electrons orbiting the nucleus.
Final Answer: The proton number of oxygen is 8, showing it has 8 protons in its nucleus and 8 electrons surrounding it.
Mass Number / Nucleon Number
The mass number (also called the nucleon number) is the total number of protons and neutrons in the nucleus of an atom. It is represented by the symbol A.
Key Points:
- Protons and neutrons are both found in the nucleus and are collectively known as nucleons.
- The mass number therefore tells you the total number of nucleons in the atom.
- Electrons are not included in the mass number because their mass is extremely small (≈ 1/1836 of a proton).
\(\mathrm{Mass \ number \ (A) = Number \ of \ protons + Number \ of \ neutrons}\)
Relationship Between Atomic and Mass Numbers:
\(\mathrm{^{A}_{Z}X}\)
- \( \mathrm{X} \) = chemical symbol of the element.
- \( \mathrm{A} \) = mass (nucleon) number = total protons + neutrons.
- \( \mathrm{Z} \) = proton (atomic) number = number of protons.
Therefore:
\(\mathrm{Number \ of \ neutrons = A – Z}\)
Example – Carbon Atom:
\(\mathrm{^{12}_{6}C}\)
- Proton number (\(Z\)) = 6 → 6 protons.
- Mass number (\(A\)) = 12 → total of 12 protons and neutrons.
- Neutrons = \(A – Z = 12 – 6 = 6\).
Conclusion: The carbon atom has 6 protons and 6 neutrons in its nucleus.
Key Differences Between Atomic Number and Mass Number:
| Property | Atomic Number (Z) | Mass Number (A) |
|---|---|---|
| Definition | Number of protons in the nucleus | Number of protons + neutrons in the nucleus |
| Symbol | Z | A |
| Determines | Element identity | Isotope type of the element |
| Example (Carbon) | 6 | 12 |
Key Idea:
The mass number (A) tells you the total number of nucleons (protons + neutrons) in the atom’s nucleus.
\(\mathrm{A = p + n}\)
Example :
An atom of magnesium is written as \(\mathrm{^{24}_{12}Mg}\). State the number of protons, neutrons, and electrons in this atom.
▶️ Answer/Explanation
Step 1: Proton number = 12 → 12 protons.
Step 2: Mass number = 24 → total protons + neutrons = 24.
Step 3: Neutrons = 24 – 12 = 12.
Step 4: In a neutral atom, electrons = protons → 12 electrons.
Final Answer: 12 protons, 12 neutrons, and 12 electrons.
Electronic Configuration of Elements (Proton Number 1–20)
The electronic configuration (or electron arrangement) shows how electrons are distributed in the shells (energy levels) around the nucleus of an atom. Electrons fill the shells in a fixed order the lowest energy level fills first.
1. Rules for Filling Electron Shells:
- Electrons fill shells in order of increasing energy (starting closest to the nucleus).
- The maximum number of electrons per shell is:
- 1st shell → 2 electrons
- 2nd shell → 8 electrons
- 3rd shell → 8 electrons (for the first 20 elements)
- Each shell must be filled before electrons move to the next shell.
\(\mathrm{Maximum \ per \ shell: \ 2, \ 8, \ 8, \ …}\)
2. Step-by-Step Method to Determine Electronic Configuration:
- Step 1: Identify the proton number (atomic number) — this equals the number of electrons in a neutral atom.
- Step 2: Place electrons into shells using the 2,8,8 rule.
- Step 3: Write the configuration as a sequence separated by commas (e.g., 2,8,3).
3. Example Calculations:
- Hydrogen (Z = 1): 1 electron → 1 → Configuration: 1
- Carbon (Z = 6): 6 electrons → 2,4 → Configuration: 2,4
- Sodium (Z = 11): 11 electrons → 2,8,1 → Configuration: 2,8,1
- Aluminium (Z = 13): 13 electrons → 2,8,3 → Configuration: 2,8,3
- Calcium (Z = 20): 20 electrons → 2,8,8,2 → Configuration: 2,8,8,2
Electronic Configurations of Elements (1–20)
| Element | Symbol | Proton Number | Electronic Configuration |
|---|---|---|---|
| Hydrogen | H | 1 | 1 |
| Helium | He | 2 | 2 |
| Lithium | Li | 3 | 2,1 |
| Beryllium | Be | 4 | 2,2 |
| Boron | B | 5 | 2,3 |
| Carbon | C | 6 | 2,4 |
| Nitrogen | N | 7 | 2,5 |
| Oxygen | O | 8 | 2,6 |
| Fluorine | F | 9 | 2,7 |
| Neon | Ne | 10 | 2,8 |
| Sodium | Na | 11 | 2,8,1 |
| Magnesium | Mg | 12 | 2,8,2 |
| Aluminium | Al | 13 | 2,8,3 |
| Silicon | Si | 14 | 2,8,4 |
| Phosphorus | P | 15 | 2,8,5 |
| Sulfur | S | 16 | 2,8,6 |
| Chlorine | Cl | 17 | 2,8,7 |
| Argon | Ar | 18 | 2,8,8 |
| Potassium | K | 19 | 2,8,8,1 |
| Calcium | Ca | 20 | 2,8,8,2 |
Key Idea:
The electronic configuration shows the number of electrons in each shell, and determines the chemical properties of the element.
Outer shell electrons = valence electrons, which control reactivity.
Example Question :
Write the electronic configuration of an atom with proton number 13.
▶️ Answer/Explanation
Step 1: Proton number = 13 → 13 electrons.
Step 2: Fill shells: 2 in 1st, 8 in 2nd, 3 in 3rd.
Step 3: Configuration = 2,8,3.
Final Answer: The atom has an electronic configuration of 2,8,3.
Relationship Between Electronic Configuration, Group Number, and Period Number
Key Statements:
- (a) Elements in Group VIII (or Group 18), the noble gases, have a full outer electron shell.
- (b) For elements in Groups I to VII (1 to 7), the number of outer-shell electrons is equal to the group number.
- (c) The number of occupied electron shells is equal to the period number.
1. Group VIII / Group 18 – Noble Gases:
- The noble gases have completely filled outer shells.
- This makes them very stable and unreactive (inert).
| Element | Symbol | Proton Number | Electronic Configuration | Outer Shell |
|---|---|---|---|---|
| Helium | He | 2 | 2 | Full (2e⁻) |
| Neon | Ne | 10 | 2,8 | Full (8e⁻) |
| Argon | Ar | 18 | 2,8,8 | Full (8e⁻) |
Conclusion: Noble gases are unreactive because they have full outer shells — they do not need to gain or lose electrons.
2. Group Number and Outer-Shell Electrons (Groups I–VII):
- For elements in Groups 1–7, the number of electrons in the outer shell is the same as the group number.
| Group | Example Element | Electronic Configuration | Outer Shell Electrons |
|---|---|---|---|
| Group 1 | Sodium (Na) | 2,8,1 | 1 |
| Group 2 | Magnesium (Mg) | 2,8,2 | 2 |
| Group 3 | Aluminium (Al) | 2,8,3 | 3 |
| Group 7 | Chlorine (Cl) | 2,8,7 | 7 |
Conclusion: Group number = number of electrons in outer shell.
3. Period Number and Electron Shells:
- The period number tells you the number of occupied electron shells.
- For example:
- Sodium (Na): 2,8,1 → 3 shells → Period 3.
- Oxygen (O): 2,6 → 2 shells → Period 2.
- Calcium (Ca): 2,8,8,2 → 4 shells → Period 4.
\(\mathrm{Period \ number = Number \ of \ electron \ shells}\)
| Property | Determined By | Example |
|---|---|---|
| Group Number | Number of outer-shell electrons | Na → 2,8,1 → Group 1 |
| Period Number | Number of occupied electron shells | Cl → 2,8,7 → Period 3 |
| Noble Gas (Group 8 / 18) | Full outer shell of electrons | Ne → 2,8 |
Example :
An element has the electronic configuration 2,8,6. State its group number and period number, and name the element.
▶️ Answer/Explanation
Step 1: Configuration = 2,8,6 → 3 shells → Period 3.
Step 2: 6 electrons in outer shell → Group 6.
Step 3: Element in Group 6, Period 3 = Sulfur (S).
Final Answer: Group = 6 | Period = 3 | Element = Sulfur (S)