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C2.6 · Investigate substance properties to infer bonding type

Learn to investigate substance properties to infer bonding type through clear examples and targeted practice.

Ontario Grade 12 Chemistry

Structure and Properties of Matter

SCH4U study topic C2.6

A solid may dissolve in water but not conduct electricity as a solid. Another solid may conduct electricity and bend without breaking. These observations are clues about how particles are joined and how they can move. In this lesson, you will connect properties to particle models, then use a set of observations to infer a likely bonding type. A property is evidence, not a label by itself: more than one type of substance can share a property.

What you will learn

Describe how observable properties can provide evidence about bonding type.
Relate particle-level models of ionic, molecular covalent, network covalent, and metallic substances to their properties.
Use several property observations together to make and explain a cautious inference.

1. From observable properties to particle models

In earlier chemistry, you learned that atoms can form ions by gaining or losing electrons, or share electrons in covalent bonds. You also learned that matter is made of particles. Here, use those ideas to ask how particles are arranged and whether charged particles or electrons can move.

A useful investigation records properties that can be observed or tested: state at room temperature, melting point, hardness or flexibility, solubility in water, and electrical conductivity. Conductivity means the ability to carry electric charge. Test conductivity in more than one state when appropriate. A substance that does not conduct as a solid might conduct when melted or dissolved.

Solubility means how much of a substance dissolves in a specified liquid. Water is a polar liquid, meaning its molecules have an uneven distribution of charge. Solubility in water can help distinguish substances, but it is not proof of a bonding type. Some molecular substances dissolve, and some ionic substances are only slightly soluble.

Melting point is the temperature at which a solid becomes a liquid. It can indicate how strongly particles are held in a solid, but it does not identify bonding on its own. Compare several properties instead of relying on one test.

Record observations before proposing an explanation.
Use multiple properties as evidence.
A property alone rarely identifies bonding type.

2. What the common bonding types suggest

Ionic substances are made of positive and negative ions arranged in a repeating solid structure. The attractions between oppositely charged ions hold the structure together. Many ionic substances are hard, brittle solids with relatively high melting points. Brittle means that a material tends to crack rather than bend. In the solid, the ions are held in place, so they cannot carry charge through the substance. When an ionic substance is molten or dissolved in water, some ions can move and carry charge. Many ionic substances dissolve in water, but not all do.

Molecular covalent substances consist of separate molecules. Atoms within each molecule share electrons. In many such substances, the attractions between separate molecules are weaker than the bonds within each molecule. This often leads to lower melting and boiling points than those of ionic or network covalent substances. Many molecular substances do not conduct electricity because they do not have mobile charged particles. Their solubility varies: some dissolve in water, while others dissolve better in non-polar liquids.

Network covalent substances have atoms connected by covalent bonds in an extended structure rather than in separate molecules. These substances are often very hard and have high melting points. They generally do not conduct electricity, although there are important exceptions. For example, graphite conducts electricity, so conductivity must be interpreted with other evidence rather than used as a universal rule.

Metallic substances contain metal atoms arranged in a structure with mobile electrons. These electrons can move through the solid and carry charge. Metals are generally good electrical conductors as solids. Many can be hammered into shape or drawn into wires without breaking; this ability is called malleability and ductility. Metallic substances are usually not soluble in water. Their melting points vary, so melting point alone is not a reliable identifier.

Ionic: ions fixed in the solid, but able to move when molten or dissolved.
Molecular covalent: separate molecules; usually poor electrical conductivity.
Network covalent: extended covalent structure; often hard with a high melting point.
Metallic: mobile electrons account for electrical conductivity in the solid.

3. Making a careful inference

Begin with the observations, not a guess based only on a formula or appearance. Look for a pattern. A solid that conducts electricity and can be shaped without shattering is consistent with metallic bonding. A solid that does not conduct, but conducts after dissolving in water, is consistent with an ionic substance if the solution contains mobile ions. A substance with a low melting point and poor conductivity in both solid and dissolved forms may be molecular covalent, provided the other observations fit.

Treat each property as supporting or weakening a possibility. For example, high melting point supports an ionic or network covalent model more than it supports many molecular substances. It does not distinguish ionic from network covalent by itself. Conductivity of a solid can help distinguish a typical metal from an ionic solid, but graphite is a reminder that exceptions exist.

A conclusion should state the likely bonding type and cite the evidence. It should also recognize uncertainty if the available properties do not separate two possibilities. This is the purpose of investigating properties: use a set of results to build the best-supported particle model, rather than claiming that one test proves the answer.

Match the full set of observations to a particle model.
State evidence and acknowledge uncertainty where needed.
Do not treat a general pattern as an exception-free rule.

Worked example

Interpreting a set of property observations

A hypothetical unknown solid is brittle and has a high melting point. It does not conduct electricity as a solid. A water solution made from it conducts electricity. Which bonding type is best supported? Explain how each observation contributes. These are supplied observations for reasoning, not claimed results of a laboratory investigation.

Identify the useful clues
The high melting point and brittleness fit the common pattern for an ionic solid. The lack of conductivity in the solid also fits because ions in the solid structure are not free to move.
Connect solution conductivity to particles
The solution conducts, so it contains charged particles that can move and carry charge. An ionic substance that dissolves can produce mobile ions in water. Together, this evidence supports an ionic model.
State the inference
The best-supported inference is ionic bonding. The conclusion is based on the full pattern, not on one property. The observations do not identify the exact ions or formula.

Answer: Ionic bonding is best supported: the solid is brittle, has a high melting point, and does not conduct as a solid, while its water solution conducts. These observations fit a solid made of fixed ions that can move after dissolving.

Check: The inference explains both the non-conducting solid and conducting solution using the same particle model.

Common mistakes and how to avoid them

Concluding that any substance that dissolves in water is ionic.

Correction: Some molecular substances dissolve in water too. Check conductivity and other properties before inferring bonding type.

Expecting an ionic solid to conduct electricity because it contains ions.

Correction: In a solid ionic structure, ions are held in place. Conductivity is expected when ions can move, such as in a solution or molten sample.

Using high melting point as proof of ionic bonding.

Correction: High melting points can also fit network covalent substances. Use additional properties to distinguish possibilities.

Treating every substance in a bonding category as having identical properties.

Correction: Use words such as usually and often. Exceptions and variations mean that a conclusion should rest on several observations.

Lesson summary

Investigate observable properties such as conductivity, solubility, melting point, and brittleness or malleability.
Use particle models to explain why a property is expected for a bonding type.
Infer bonding type from a pattern of evidence, not from a single property.
Communicate the conclusion with supporting observations and appropriate caution.

Check your understanding

Question 1

A solid conducts electricity and can be hammered into a new shape without crumbling. Which bonding type is most strongly suggested?

Metallic
Ionic
Molecular covalent
Network covalent

Show answer and explanation

Metallic

Conductivity in the solid and the ability to be shaped are both consistent with metallic substances, which have mobile electrons and are often malleable.

Question 2

Why might an ionic substance conduct electricity in water but not as a solid?

Its ions can move in solution but are held in place in the solid.
Its atoms become metallic when water is added.
Its covalent bonds conduct only in liquid water.
Its solid has no charged particles.

Show answer and explanation

Its ions can move in solution but are held in place in the solid.

The solid contains ions, but they are fixed in the solid structure. When dissolved, mobile ions can carry charge.

Question 3

A substance has a high melting point. What is the strongest conclusion from this observation alone?

It must be ionic.
It must be metallic.
The observation is a clue, but more properties are needed.
It must be molecular covalent.

Show answer and explanation

The observation is a clue, but more properties are needed.

High melting point can fit more than one bonding type. Other observations are needed to make a stronger inference.

Key terms

Conductivity: The ability of a material to carry electric charge.
Solubility: How much of a substance dissolves in a specified liquid.
Brittle: Likely to crack or break rather than bend.
Malleability: The ability of a material to be hammered or shaped without breaking.
Network covalent: A structure in which atoms are connected by covalent bonds in an extended arrangement, not as separate molecules.

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About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 12 Chemistry (SCH4U), expectation C2.6. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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