Grade 10 chemisty Inorganic Chemistry – The Periodic Table Notes

Inorganic Chemistry — The Periodic Table

Target learners: Kenyan students, age ≈15 years (about Form 3). Short notes, simple diagrams and activities to meet the Specific Learning Outcomes below.

Specific Learning Outcomes

• a) Relate the position of an element in the periodic table to its electron arrangement.
• b) Illustrate ion formation of elements.
• c) Derive the formulae of compounds.
• d) Write balanced chemical equations for simple reactions.
• e) Appreciate the role of electron arrangement in the development of the periodic table.

Key ideas — short notes

1. Periods and groups (position and electrons)

- Period (row) number = number of electron shells occupied. Example: elements in Period 3 have 3 shells.
- Group (column) number (for main-group elements) shows valence electrons. Example: Group 1 elements have 1 valence electron (very reactive metals); Group 17 have 7 valence electrons (reactive non-metals); Group 18 are noble gases (full outer shell).

2. Electron arrangement (simple notation)

- Write electron arrangement as numbers of electrons in shells: e.g., Na (atomic number 11): 2, 8, 1. Cl (17): 2, 8, 7. Mg (12): 2, 8, 2.
- The outer (valence) electrons determine chemical behaviour: bonding, ion formation and reactivity.

3. Ion formation (loss/gain of electrons)

- Metals tend to lose electrons to form positive ions (cations). Non-metals tend to gain electrons to form negative ions (anions). Examples:

4. How ions form useful formulas

- To make a neutral ionic compound, total positive charge = total negative charge. Use the criss-cross method to get simplest formula.

5. Writing balanced chemical equations

Steps to balance: (1) write reactants and products; (2) count atoms of each element on both sides; (3) change coefficients (whole numbers) to balance; (4) check that charge (if ionic) and mass are conserved.

6. Development of the periodic table & electron arrangement

- Early periodic table (Mendeleev) ordered elements by increasing atomic mass and grouped similar properties together; gaps left for undiscovered elements.
- Modern periodic table is ordered by increasing atomic number (number of protons). Periodic trends (which follow from electron arrangement) include atomic radius, ionization energy, and electronegativity. The repeating pattern of properties is due to repeating electron configurations across periods.

Suggested learning experiences (class activities & practicals)

1. Card sorting (class): Give students element cards (symbol, atomic number). Ask them to arrange into a simplified periodic table (first 20 elements). Have them write electron arrangement on each card and explain group/period positions.
2. Bohr model drawing (pair work): Students draw Bohr diagrams for Na, Mg, O, Cl and then show how electrons are lost/gained to form ions. Use the SVG diagrams above as models.
3. Model building (hands-on): Use beads or stickers to build ionic compounds: assemble Na⁺ and Cl⁻ “ions” into neutral NaCl units; Mg²⁺ with two Cl⁻ units for MgCl2.
4. Safe classroom practical — neutralisation to make salt: React dilute HCl with dilute NaOH to produce NaCl and water. Balanced equation: HCl + NaOH → NaCl + H2O. (Do in small volumes, use protective equipment, teacher demonstration if required.)
5. Observational practical (teacher demo): Burn a magnesium ribbon to form magnesium oxide (2 Mg + O2 → 2 MgO). Students observe light and ash, then write balanced equation and describe electron changes (Mg → Mg²⁺ in MgO ionic lattice).
6. Group discussion / history: Students research how Mendeleev predicted properties of undiscovered elements and link that to modern ordering by atomic number and electron arrangement.
7. Role-play / game: Pupils act as electrons: arrange themselves in energy levels and move between atoms to demonstrate ion formation and bonding (helps weaker learners).

Assessment tasks (short)

1. Write the electron arrangement of: O (Z=8), Ca (Z=20), and F (Z=9). (Answers: O 2,6; Ca 2,8,8,2; F 2,7)
2. Predict the ion formed by potassium (K, Z=19) and write its symbol.
3. Give the formula for the compound formed between Al³⁺ and S²⁻. (Answer: Al2S3)
4. Balance and name the reaction: Al + O2 → Al2O3. (Balanced: 4 Al + 3 O2 → 2 Al2O3)
5. Explain in two sentences why elements in the same group have similar chemical properties.

Safety notes for practicals

• Always wear eye protection and gloves when handling acids, bases or hot metals.
• Perform reactive metal demonstrations (e.g., sodium metal) only as teacher demonstrations with proper safety; avoid student handling.
• Dispose of chemicals according to school rules and wash hands after experiments.

Summary (one paragraph)

The periodic table organises elements by increasing atomic number and shows repeating patterns (periodicity) because of electron arrangement. The position of an element (period and group) tells you how many electron shells it has and how many valence electrons — this predicts ion formation and bonding. By knowing the ions produced we can derive chemical formulae and write balanced equations for reactions. Understanding electron arrangement is therefore central to both the modern periodic table and to predicting chemical behaviour.

Prepared for classroom use — adapt activities and demonstrations to your school laboratory facilities and safety guidelines.