1.1.1Reactivity 1 — What drives chemical reactions?
Chemical Elements, Compounds and Mixtures — IB Chemistry SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 4 of 8 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Pure Substances
A pure substance has a fixed composition and fixed properties.
Element
- Element A substance made of only one type of atom, which cannot be broken down into simpler substances by chemical methods.
Compound
- Compound A substance made of two or more elements chemically combined in a fixed ratio, such as H₂O or NaCl.
Properties
- Properties A compound's properties differ greatly from those of its elements, as sodium and chlorine differ from sodium chloride.
Separation
- Separation A compound can be split into its elements only by a chemical reaction, such as electrolysis or heating.
Part 2 of 4Mixtures
A mixture contains two or more substances that are not chemically bonded.
Variable composition
- Variable composition The proportions of the components can change from one sample to another, unlike in a compound.
Retained properties
- Retained properties Each component keeps its own chemical properties, so a mixture of iron and sulfur is still attracted by a magnet.
Homogeneous
- Homogeneous Has a uniform composition throughout and appears as a single phase, as in salt dissolved in water or air.
Heterogeneous
- Heterogeneous Has non-uniform composition with visibly different phases, as in sand and water or oil and vinegar.
| Feature | Element | Compound | Mixture |
|---|---|---|---|
| Composition | One type of atom | Fixed ratio of elements | Variable |
| Bonding between components | None between types | Chemical bonds | None |
| Separated by | Cannot be split chemically | Chemical reaction | Physical methods |
Part 3 of 4Particle Pictures
Diagrams of particles can identify what a sample is.
1
An element is drawn with identical particles, either single atoms or molecules made of the same kind of atom.
2
A compound is drawn with identical particles, each one containing at least two different kinds of atom bonded together.
3
A mixture of elements or compounds shows two or more different kinds of particle that are not bonded to each other.
4
To tell a mixture of two gases from a compound, look for whether different atoms are joined within the same particle.
Part 4 of 4Exam Checklist & Tips
1.1.1 – Key Points for the Exam
- Element A pure substance containing only one type of atom.
- Compound A pure substance of two or more elements chemically bonded in a fixed ratio.
- Homogeneous mixture A mixture with uniform composition and a single phase.
- Heterogeneous mixture A mixture with non-uniform composition and distinct phases.
Common Mistakes
- Saying a molecule of oxygen, O₂, is a compound; it contains only one type of atom, so it is an element.
- Calling all clear liquids pure substances; salt solution is a clear mixture.
- Thinking that air is a compound rather than a homogeneous mixture of gases.
- Assuming a mixture has a fixed formula or melting point like a pure substance.
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