Chemical Bonding and Reactions
MYP Unit Framework
Key Concept: CHANGE Related Concepts: Energy. Interaction. Evidence. Global Context: Scientific and Technical Innovation (How can we model chemical change at the molecular level and harness it for human purposes?) Statement of Inquiry: Chemical change involves energy transformations that can be modelled at the molecular level and harnessed for human purposes.
Inquiry Questions
| Type | Question |
|---|---|
| Factual | What are ionic, covalent, and metallic bonds? What are the different types of chemical reactions? How do you balance a chemical equation? What is a mole? |
| Conceptual | Why do atoms BOND in the first place? How is energy STORED in chemical bonds — and RELEASED in reactions? How can we PREDICT the products of a reaction? |
| Debatable | Should we continue to use FOSSIL FUELS as chemical feedstocks — or transition to renewable alternatives? Is industrial chemistry doing more HARM than GOOD to the environment? |
1. Why Atoms Bond — The Octet Rule
The Drive Toward Stability
'Atoms bond to achieve a MORE STABLE electron configuration — usually a full OUTER SHELL (octet) of electrons. Noble gases (Group 18) are stable because they already have a full outer shell. Other atoms gain, lose, or share electrons to ACHIEVE the same configuration.'
'This drive toward the octet EXPLAINS nearly everything about chemical bonding — why sodium (1 electron in its outer shell) readily LOSES that electron, why chlorine (7 electrons) readily GAINS one, and why carbon (4 electrons) SHARES electrons with other atoms.'
Electronegativity — The Tug-of-War
'Electronegativity is a measure of how STRONGLY an atom ATTRACTS electrons in a bond. Fluorine is the most electronegative element (4.0). Francium is the least (0.7). The DIFFERENCE in electronegativity between two bonded atoms determines the TYPE of bond that forms.'
2. Ionic Bonding — Transferring Electrons
How Ionic Bonds Form
'Ionic bonding involves the COMPLETE TRANSFER of electrons from one atom to another. This typically occurs between a METAL (low electronegativity) and a NON-METAL (high electronegativity).'
Example — Sodium chloride (NaCl): 'Sodium (Na) has 1 electron in its outer shell. It LOSES this electron to become Na⁺ (a cation). Chlorine (Cl) has 7 electrons in its outer shell. It GAINS an electron to become Cl⁻ (an anion). The OPPOSITE charges attract — forming an IONIC BOND.'
Properties of Ionic Compounds
- High melting and boiling points: Strong electrostatic forces between ions require a LOT of energy to overcome.
- Conduct electricity when MOLTEN or DISSOLVED: Ions are FREE to move in the liquid or solution — but NOT in the solid state.
- Soluble in water: Water molecules are POLAR and can surround and separate the ions.
- Form CRYSTAL LATTICES: Ions arrange themselves in REGULAR, REPEATING patterns. 'The crystal lattice of NaCl is a CUBIC arrangement — each Na⁺ ion is surrounded by SIX Cl⁻ ions, and vice versa.'
3. Covalent Bonding — Sharing Electrons
How Covalent Bonds Form
'Covalent bonding involves the SHARING of electrons between atoms. This typically occurs between TWO NON-METALS with SIMILAR electronegativities. The shared electrons are ATTRACTED to BOTH nuclei — this mutual attraction holds the atoms together.'
Types of covalent bonds:
| Bond type | Shared electron pairs | Example |
|---|---|---|
| Single bond | 1 pair | H–H, C–H |
| Double bond | 2 pairs | C=O, O=O |
| Triple bond | 3 pairs | N≡N, C≡C |
'The more electron pairs shared, the STRONGER and SHORTER the bond. Triple bonds are the strongest — but also the MOST REACTIVE under certain conditions.'
Polar and Non-Polar Covalent Bonds
'When electrons are shared EQUALLY — as in H₂ — the bond is NON-POLAR. When electrons are shared UNEQUALLY — as in H₂O — the bond is POLAR. One end of the bond has a SLIGHT positive charge, the other a SLIGHT negative charge.'
'This POLARITY is responsible for MANY of water's unique properties — its high surface tension, its ability to dissolve many substances, and the fact that it is LESS DENSE as a solid (ice floats).'
Properties of Covalent Compounds
- Low melting and boiling points: Weak INTERMOLECULAR forces between molecules.
- Do NOT conduct electricity: No free ions or electrons.
- Often INSOLUBLE in water: Non-polar substances do not dissolve well in polar water.
- Can be GASES, LIQUIDS, or SOLIDS at room temperature, depending on molecular size and intermolecular forces.
4. Metallic Bonding — The Sea of Electrons
The Metallic Bond Model
'In a metal, atoms are arranged in a CLOSE-PACKED lattice. Their OUTER electrons become DELOCALISED — they are free to move through the entire structure. The metal consists of POSITIVE IONS immersed in a "SEA OF ELECTRONS."'
Properties of Metals
- Conduct electricity: Delocalised electrons can MOVE through the metal when a voltage is applied.
- Conduct heat: Delocalised electrons TRANSFER kinetic energy quickly.
- Malleable and ductile: Layers of positive ions can SLIDE over each other without breaking the bond — the electron sea ADAPTS.
- High melting and boiling points: Strong metallic bonds require significant energy to overcome.
5. Types of Chemical Reactions
| Reaction Type | General Form | Example |
|---|---|---|
| Synthesis | A + B → AB | 2Mg + O₂ → 2MgO |
| Decomposition | AB → A + B | 2H₂O → 2H₂ + O₂ |
| Single displacement | A + BC → AC + B | Zn + CuSO₄ → ZnSO₄ + Cu |
| Double displacement | AB + CD → AD + CB | AgNO₃ + NaCl → AgCl + NaNO₃ |
| Combustion | Hydrocarbon + O₂ → CO₂ + H₂O | CH₄ + 2O₂ → CO₂ + 2H₂O |
| Redox (Reduction-Oxidation) | Electron transfer | 2Fe₂O₃ + 3C → 4Fe + 3CO₂ |
Energy Changes — Exothermic and Endothermic
'Every chemical reaction involves ENERGY CHANGE. In EXOTHERMIC reactions, energy is RELEASED (usually as heat) — the products have LESS chemical energy than the reactants. In ENDOTHERMIC reactions, energy is ABSORBED — the products have MORE chemical energy than the reactants.'
'Activation energy (Eₐ) is the MINIMUM energy required for a reaction to occur. Catalysts lower the activation energy — speeding up the reaction WITHOUT being consumed.'
6. Stoichiometry — The Mathematics of Chemistry
The Mole — Chemist's Counting Unit
'A MOLE is 6.02 × 10²³ particles — Avogadro's number. One mole of ANY substance has a mass equal to its relative formula mass in grams. 'The mole allows chemists to COUNT atoms and molecules by WEIGHING them — because you cannot COUNT atoms individually.'
Balancing Equations
'A balanced chemical equation has the SAME number of each type of atom on BOTH sides. Balancing equations is ESSENTIAL for stoichiometric calculations — because the coefficients tell you the RELATIVE amounts of reactants and products.'
Stoichiometric Calculations
The MOLE RATIO from the balanced equation allows you to PREDICT:
- How much PRODUCT will form from a given amount of reactant.
- How much REACTANT is needed to produce a desired amount of product.
Limiting reactant: 'The reactant that is CONSUMED FIRST limits the amount of product that can form. The other reactant is IN EXCESS. Finding the limiting reactant is ESSENTIAL in industrial chemistry — it tells you which reactant is the BOTTLENECK.'
Percentage Yield
'Actual yield is what you ACTUALLY get. Theoretical yield is what you SHOULD get based on stoichiometry. Percentage yield = (actual ÷ theoretical) × 100%. Yields are ALMOST NEVER 100% — due to incomplete reactions, side reactions, and losses during purification.'
7. Industrial Chemistry — Applications
Haber-Bosch process: 'N₂ + 3H₂ → 2NH₃. The Haber-Bosch process FIXES atmospheric nitrogen into ammonia — which is used as FERTILISER. It is arguably the MOST IMPORTANT chemical reaction in human history. Without it, we could not feed 8 billion people. But it also consumes about 2% of the world's energy — and produces significant CO₂ emissions.'
Contact process: 'Production of sulphuric acid — the MOST PRODUCED chemical by volume in the world. Used in fertilisers, plastics, dyes, detergents, and petroleum refining.'
Your Summative Assessment — The Stoichiometry Lab Report
Task: Conduct a TITRATION experiment (strong acid + strong base) to determine the CONCENTRATION of an unknown acid. Write a FULL LAB REPORT including: Aim, Hypothesis, Materials, Method, Results (raw data table, processed data, calculations), Conclusion, and Evaluation. Your calculations must include: balanced equation, mole calculations using concentration and volume, determination of the unknown concentration, and error analysis.
'This is a STANDARD practical in IB DP Chemistry. Mastering the titration technique — and the stoichiometric calculations — is ESSENTIAL for success in Diploma Programme sciences.'
ATL Skills
| Skill | Focus |
|---|---|
| Critical Thinking | Analysing data, identifying sources of error, evaluating experimental design. |
| Research | Investigating industrial applications of chemical reactions. |
| Communication | Writing a structured lab report with correct scientific conventions. |
| Self-Management | Following experimental procedures safely and accurately. |
Formative Assessments
| Assessment | Focus |
|---|---|
| Bonding types chart | Create a chart comparing ionic, covalent, and metallic bonding across key properties. |
| Balancing equations drill | Balance 10 unbalanced chemical equations of varying difficulty. |
| Stoichiometry problem set | Solve a set of mass-mass, mole-mole, and limiting reactant problems. |
| Reaction prediction | Predict the products of 5 given reactions and write balanced equations. |
Interdisciplinary Connections
- Physics: Energy changes, electricity, and conductivity in bonding.
- Mathematics: Stoichiometric calculations, ratio and proportion, significant figures.
- Environmental Science: Industrial chemistry impacts, green chemistry principles.
- TOK: Are models (like the 'sea of electrons') 'true' — or just USEFUL fictions?
Service as Action
- Water quality testing: Test the pH and chemical composition of local water sources.
- Green chemistry audit: Evaluate cleaning and lab chemicals used in your school for environmental impact.
- Science demonstration: Create a safe chemistry demonstration for younger students.
IB Learner Profile Attributes
| Attribute | How This Unit Develops It |
|---|---|
| Inquirers | Students investigate the fundamental nature of chemical change. |
| Thinkers | Students solve quantitative problems and evaluate experimental data. |
| Knowledgeable | Students build deep understanding of bonding, reactions, and stoichiometry. |
| Principled | Students consider the ethical and environmental dimensions of industrial chemistry. |
Self-Test Questions
-
Explain the OCTET RULE. How does it explain ionic, covalent, and metallic bonding?
-
Compare ionic and covalent bonding across THREE properties (melting point, conductivity, solubility).
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Balance the following equation: Fe + O₂ → Fe₂O₃. Then calculate how many grams of Fe₂O₃ form from 10.0 g of Fe.
-
What is a MOLE? Why is Avogadro's number useful in chemistry?
-
Define exothermic and endothermic reactions. Give an example of each.
-
What is the limiting reactant? How does it affect the amount of product formed?
-
Describe ONE industrial chemical process and its importance to society. What are the environmental implications?
