Metals and alloys: distort the layers to resist sliding
הוצג| English | משמעות |
|---|---|
| alloy/ˈælɔɪ/ | סגסוגת |
| hardness/ˈhɑːdnəs/ | קשיחות |
What would explain this observation?
- A pure metal’s regular layers can slide when a force is applied. Introducing different-sized atoms can hinder that sliding, helping explain why an alloy 合金 is harder.
Build the model
- Most metals have high melting and boiling points because their giant structures have strong metallic bonding.
- Atoms in a pure metal are represented in regular layers, which can move past one another while attraction to delocalised electrons persists.
- This permits bending and shaping.
- Pure metals can be too soft for particular uses, so they are mixed with other elements to form alloys.
- alloy: A metallic mixture containing a metal and one or more other elements.
- hardness 硬度: Resistance of a material to indentation or scratching.
Why can an alloy be harder than its pure metal?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
The added atoms are a different size, so they distort the regular layers and stop them sliding over each other - that resistance to slip is hardness. No new element forms, and no electrons leave.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Different-sized atoms distort the regular layers and make sliding more difficult, so many alloys are harder than the corresponding pure metal.
- Hardness is resistance to indentation or scratching, while strength concerns resisting deformation or failure under a load; do not treat the words as identical measurements.
- An alloy still has metallic bonding and need not have one fixed compound formula.
In the lab: Compare equal-size atom layers with a model containing some larger atoms. Show the disruption and explain its effect rather than merely saying alloy atoms are bigger. Use supplied hardness data and actual teacher-approved samples with suitable tools. Compare the same test method and conditions; an arbitrary harder sample does not establish how every possible alloy behaves.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: supplied model hardness values are 40 units for a pure metal and 70 for an alloy measured by the same method.
- Increase=70−40=30 units; percentage increase=30/40×100=75%.
- These fictional values quantify one comparison and are not universal values or a complete explanation of the structural cause.
Your turn: A supplied hardness rises from 50 to 80 units. Calculate the percentage increase.
A supplied hardness rises from 50 to 80 units. Calculate the percentage increase.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 60 %. Known: hardness rises from 50 to 80 units. Increase = 30 units. Percentage increase = 30/50 x 100 = 60%. These are model values for one comparison, not universal constants.
Check the conclusion and its limits
- An alloy is a mixture, not automatically a new compound with fixed proportions.
- Added atoms hinder sliding without removing all delocalised electrons.
- A layer model omits real defects and three-dimensional detail, and high melting point is typical rather than universal for metals.
Not true: An alloy must always be a compound with one fixed atom ratio. An alloy is a MIXTURE of metals (or metals with carbon) whose proportions can vary. A compound has a fixed ratio and new bonding; brass is 60-80% copper without ever becoming a compound.
- Most metals have high melting and boiling points because their giant structures have strong metallic bonding.
- Different-sized atoms distort the regular layers and make sliding more difficult, so many alloys are harder than the corresponding pure metal.
- Watch for: an alloy is a mixture, not automatically a new compound with fixed proportions.
An alloy is a MIXTURE of metals (or metals with carbon) whose proportions can vary.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. An alloy is a MIXTURE of metals (or metals with carbon) whose proportions can vary. A compound has a fixed ratio and new bonding; brass is 60-80% copper without ever becoming a compound.
A metallic mixture containing a metal and one or more other elements: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
alloy means A metallic mixture containing a metal and one or more other elements.