CIE iGCSE Co-ordinated Sciences-C8.1 Arrangement of elements- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C8.1 Arrangement of elements – Study Notes
CIE iGCSE Co-ordinated Sciences-C8.1 Arrangement of elements – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe the Periodic Table as an arrangement of elements in periods and groups and in order of increasing proton number / atomic number
- Describe the change from metallic to non-metallic character across a period
- Explain similarities in the chemical properties of elements in the same group of the Periodic Table in terms of their electronic configuration
Supplement
- Identify trends in groups, given information about the elements
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
The Periodic Table
The Periodic Table is an arrangement of all known elements in order of their increasing proton number (atomic number). It shows how the properties of elements repeat periodically (at regular intervals).
1. Order of Arrangement:
- Elements are arranged in order of their increasing atomic number (the number of protons in the nucleus).
- As you move from left to right across the table, the atomic number increases by one for each element.
- This arrangement also reflects the increasing number of electrons in the atoms.
2. Periods:
- Horizontal rows in the Periodic Table are called periods.
- Each period shows a gradual change in properties across the row (for example, from metallic to non-metallic character).
- All elements in the same period have the same number of electron shells.
Example:
- Period 2 elements — Li, Be, B, C, N, O, F, Ne — each have two electron shells.
- As you go across the period, the number of outer electrons increases from 1 to 8.
3. Groups:
- Vertical columns in the Periodic Table are called groups.
- Elements in the same group have:
- the same number of electrons in their outer shell, and
- similar chemical properties.
- There are 8 main groups in the Periodic Table (Group 1 to Group 8 or Group 0 for noble gases).
Example:
- Group 1 (Alkali metals): Li, Na, K — 1 electron in outer shell → very reactive metals.
- Group 7 (Halogens): F, Cl, Br, I — 7 electrons in outer shell → reactive non-metals.
- Group 0 / 8 (Noble gases): He, Ne, Ar — full outer shell → very unreactive gases.
4. Key Structural Features of the Periodic Table:
- Metals are found on the left-hand side and centre.
- Non-metals are found on the right-hand side.
- A zig-zag line divides metals and non-metals.
- Group number = number of outer shell electrons (for main-group elements).
- Period number = number of electron shells.
The Periodic Table is arranged in order of increasing proton number, with elements in the same group having similar chemical properties and the same number of outer electrons.
Example :
Describe how elements are arranged in the Periodic Table and explain the meaning of ‘groups’ and ‘periods’.
▶️ Answer/Explanation
Step 1: Elements are arranged in order of increasing proton number (atomic number).
Step 2: The horizontal rows are called periods — all elements in the same period have the same number of electron shells.
Step 3: The vertical columns are called groups — all elements in the same group have the same number of outer shell electrons and similar chemical properties.
Final Answer: The Periodic Table is arranged by increasing proton number. Elements in the same group have similar chemical behaviour, while elements in the same period have the same number of electron shells.
Change from Metallic to Non-Metallic Character Across a Period
As you move across a period in the Periodic Table (from left to right), the elements gradually change from being metallic to non-metallic in character. This is because of changes in the atomic structure and electron behaviour as the proton number increases.
Metallic Character (Left Side of Period):
- Elements on the left-hand side (e.g. sodium, magnesium) are metals.
- They have:
- 1, 2, or 3 electrons in their outer shell.
- Low ionisation energies (easy to remove outer electrons).
- A tendency to lose electrons to form positive ions (cations).
- Hence, they show metallic character — good conductors of electricity and heat, malleable, and ductile.
Example: \(\mathrm{Na → Na^+ + e^-}\)
Non-Metallic Character (Right Side of Period):
- Elements on the right-hand side (e.g. chlorine, oxygen) are non-metals.
- They have:
- 5, 6, or 7 electrons in their outer shell.
- High ionisation energies (hard to remove electrons).
- A strong tendency to gain or share electrons to achieve a full outer shell.
- Hence, they show non-metallic character — poor conductors, low melting and boiling points, and form acidic oxides.
Example: \(\mathrm{Cl_2 + 2e^- → 2Cl^-}\)
Reason for the Change Across a Period:
- As the proton number increases, the nuclear charge increases.
- This pulls the outer electrons closer to the nucleus, making it more difficult to lose electrons.
- Therefore:
- Metallic character (tendency to lose electrons) decreases.
- Non-metallic character (tendency to gain/share electrons) increases.
Across a period, elements change from metals (which lose electrons easily) to non-metals (which gain or share electrons easily) because the attraction between the nucleus and outer electrons increases as proton number rises.
Example :
Describe and explain the change from metallic to non-metallic character across Period 3 of the Periodic Table.
▶️ Answer/Explanation
Step 1: In Period 3, the elements change from metals (Na, Mg, Al) to non-metals (S, Cl, Ar).
Step 2: Moving across the period, the number of outer shell electrons increases and atoms find it harder to lose electrons.
Step 3: The nuclear charge increases, pulling electrons closer to the nucleus.
Step 4: Thus, metallic character decreases while non-metallic character increases across the period.
Final Answer: Across a period, metallic character decreases and non-metallic character increases because atoms lose electrons less easily and tend to gain or share them instead.
Similarities in Chemical Properties of Elements in the Same Group
- Elements in the same group of the Periodic Table have similar chemical properties.
- This is because they have the same number of electrons in their outer (valence) shell.
- The outer shell electrons determine how an element reacts chemically — how easily it gains, loses, or shares electrons.
1. Explanation in Terms of Electronic Configuration:
- The chemical behaviour of an element depends mainly on its outer shell electrons.
- Elements in the same group have the same outer electron configuration.
- This means they react in a similar way to form compounds with the same general formulas.
Example — Group 1 (Alkali Metals):
| Element | Electronic Configuration | Outer Electrons | Type of Ion Formed |
|---|---|---|---|
| Lithium (Li) | 2,1 | 1 | Li⁺ |
| Sodium (Na) | 2,8,1 | 1 | Na⁺ |
| Potassium (K) | 2,8,8,1 | 1 | K⁺ |
Observation:
- All Group 1 metals have one electron in their outer shell.
- They all lose one electron to form a +1 ion when they react.
- Hence, they all react similarly — for example, with water to form a metal hydroxide and hydrogen gas.
\(\mathrm{2Na + 2H_2O → 2NaOH + H_2}\)
2. Example — Group 7 (Halogens):
| Element | Electronic Configuration | Outer Electrons | Type of Ion Formed |
|---|---|---|---|
| Fluorine (F) | 2,7 | 7 | F⁻ |
| Chlorine (Cl) | 2,8,7 | 7 | Cl⁻ |
| Bromine (Br) | 2,8,18,7 | 7 | Br⁻ |
Observation:
- All Group 7 elements have seven electrons in their outer shell.
- They all gain one electron to form a –1 ion when they react.
- Hence, they have similar reactions — for example, reacting with metals to form salts such as sodium chloride.
\(\mathrm{2Na + Cl_2 → 2NaCl}\)
The outer shell electron configuration determines the chemical properties of an element. Elements in the same group have the same number of outer electrons, so they react in similar ways.
Example :
Explain why elements in Group 1 of the Periodic Table have similar chemical properties.
▶️ Answer/Explanation
Step 1: All Group 1 elements have one electron in their outer shell.
Step 2: They all lose this one electron to form a +1 ion when they react.
Step 3: Because they form ions in the same way, their chemical reactions are similar — e.g., they all react with water to form an alkali and hydrogen gas.
Final Answer: Elements in the same group have similar chemical properties because they have the same number of outer shell electrons and therefore form ions and compounds in the same way.
Trends in Groups
Within a group of the Periodic Table, elements show predictable trends in physical and chemical properties due to their similar electronic configurations. These trends can be identified when given information about elements.
Key Trends:
- Atomic radius: Increases down a group because each element has an additional electron shell.
- Ionization energy: Decreases down a group as outer electrons are further from the nucleus and easier to remove.
- Reactivity: For metals (e.g., Group 1), reactivity increases down the group. For non-metals (e.g., Group 17), reactivity decreases down the group.
- Melting and boiling points: Can increase or decrease depending on the group (e.g., Group 1 metals have decreasing melting points down the group, while Group 17 halogens have increasing melting points down the group).
Example
Given that lithium, sodium, and potassium react with water to produce hydrogen, predict the trend in reactivity.
▶️Answer/Explanation
All three are Group 1 metals with one valence electron.
Reactivity increases down the group because the outer electron is further from the nucleus and more easily lost.
Therefore, potassium is more reactive than sodium, which is more reactive than lithium.
Example
Given that chlorine, bromine, and iodine react with potassium to form salts, predict the trend in reactivity.
▶️Answer/Explanation
All three are Group 17 halogens with seven valence electrons.
Reactivity decreases down the group because atoms are larger, and the nucleus has less attraction for an additional electron.
Therefore, chlorine is more reactive than bromine, which is more reactive than iodine.