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:
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Structure of the atom
The atom is made up of a dense central nucleus and electrons surrounding it:
Nucleus:
- Located at the center of the atom.
- Contains protons, which are positively charged particles, and neutrons, which have no charge.
- Almost all the mass of the atom is concentrated in the nucleus.
Electrons:
- Negatively charged particles that move around the nucleus in specific energy levels called electron shells.
- The electrons are arranged in shells at different distances from the nucleus, with the first shell closest to the nucleus.
- Electrons determine the chemical properties and reactivity of the atom.
The relative charges and relative masses of a proton, a neutron and an electron
| Particle | Relative Charge | Relative Mass |
|---|---|---|
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1836 ≈ 0 |
Proton number/atomic number
The proton number, also called the atomic number, is defined as the number of protons present in the nucleus of an atom. It is a unique property of each element and determines the identity of the element. For example:
- Hydrogen has 1 proton → proton number = 1
- Carbon has 6 protons → proton number = 6
- Oxygen has 8 protons → proton number = 8
The proton number also equals the number of electrons in a neutral atom, which determines the chemical behavior of the element.
Mass number/nucleon number
The mass number, also called the nucleon number, is defined as the total number of protons and neutrons in the nucleus of an atom. It represents the majority of the atom’s mass. For example:
- Carbon-12: 6 protons + 6 neutrons → mass number = 12
- Oxygen-16: 8 protons + 8 neutrons → mass number = 16
- Iron-56: 26 protons + 30 neutrons → mass number = 56
The mass number is always a whole number and is different from the relative atomic mass, which is an average of all isotopes of the element.
Example
An atom has 6 protons in its nucleus. Identify the element and its atomic number.
▶️ Answer/Explanation
The atom has 6 protons → proton number = 6 → atomic number = 6.
The element with atomic number 6 is Carbon (C).
Example
An atom has 8 protons and 8 neutrons. Determine its mass number.
▶️ Answer/Explanation
Mass number = number of protons + number of neutrons = 8 + 8 = 16.
The atom is Oxygen-16 with atomic number 8 and mass number 16.
The electronic configuration of elements
The electronic configuration of an atom shows how its electrons are arranged in shells around the nucleus. The rules for arranging electrons are:
- Electrons occupy shells in order of increasing energy levels (closest shells fill first).
- The first shell can hold up to 2 electrons, the second and third shells up to 8 electrons each, and the fourth shell up to 2 electrons (for elements 1–20).
Group VIII noble gases have a full outer shell
Noble gases (helium, neon, argon, etc.) have complete outer electron shells. This full outer shell makes them chemically very stable and largely unreactive.
The number of outer-shell electrons is equal to the group number in Groups I to VII
For elements in Groups I to VII of the periodic table, the group number corresponds to the number of electrons in their outermost shell. Examples:
- Group I (e.g., sodium, \( 2,8,1 \)) → 1 outer electron
- Group II (e.g., magnesium, \( 2,8,2 \)) → 2 outer electrons
- Group VII (e.g., chlorine, \( 2,8,7 \)) → 7 outer electrons
The number of occupied electron shells is equal to the period number
The period number indicates how many electron shells are occupied by electrons in the atom. Examples:
- Period 1 (e.g., hydrogen, helium) → 1 shell
- Period 2 (e.g., carbon, oxygen) → 2 shells
- Period 3 (e.g., sodium, magnesium) → 3 shells
| Element | Proton Number (Z) | Electronic Configuration |
|---|---|---|
| Hydrogen | 1 | 1 |
| Helium | 2 | 2 |
| Lithium | 3 | 2,1 |
| Beryllium | 4 | 2,2 |
| Boron | 5 | 2,3 |
| Carbon | 6 | 2,4 |
| Nitrogen | 7 | 2,5 |
| Oxygen | 8 | 2,6 |
| Fluorine | 9 | 2,7 |
| Neon | 10 | 2,8 |
| Sodium | 11 | 2,8,1 |
| Magnesium | 12 | 2,8,2 |
| Aluminium | 13 | 2,8,3 |
| Silicon | 14 | 2,8,4 |
| Phosphorus | 15 | 2,8,5 |
| Sulfur | 16 | 2,8,6 |
| Chlorine | 17 | 2,8,7 |
| Argon | 18 | 2,8,8 |
| Potassium | 19 | 2,8,8,1 |
| Calcium | 20 | 2,8,8,2 |
Example
An element has the electronic configuration 2,8,1. Identify the element and its group.
▶️ Answer/Explanation
Electronic configuration: 2,8,1 → total electrons = 11 → atomic number = 11 → Sodium (Na)
It has 1 electron in its outermost shell → Group I element.
Example
For the element with electronic configuration 2,8,6, how many outer-shell electrons are present?
▶️ Answer/Explanation
Electronic configuration: 2,8,6 → outermost shell = 6 electrons
Element = Sulfur (S), Group VI → 6 outer electrons.
Example
Explain why neon is chemically unreactive.
▶️ Answer/Explanation
Neon has the electronic configuration 2,8, meaning its outer shell is full. A full outer shell makes the atom stable and unreactive.
Example
Determine the group number of chlorine based on its outer-shell electrons.
▶️ Answer/Explanation
Chlorine has electronic configuration 2,8,7 → 7 electrons in the outermost shell → belongs to Group VII.