In 7th grade science, elements can be classified based on several criteria, primarily into three main categories: metals, nonmetals, and metalloids. Here’s a breakdown of each category along with examples:
1. Metals
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Characteristics:
- Good conductors of electricity and heat
- Shiny (lustrous)
- Malleable (can be hammered into thin sheets)
- Ductile (can be stretched into wires)
- Generally solid at room temperature (except mercury)
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Examples:
- Iron (Fe): Used in construction and manufacturing.
- Copper (Cu): Used in electrical wiring.
- Gold (Au): Used in jewelry and electronics.
2. Nonmetals
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Characteristics:
- Poor conductors of electricity and heat (insulators)
- Dull (not shiny)
- Brittle when solid (breaks or shatters easily)
- Many are gases at room temperature
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Examples:
- Oxygen (O): Essential for respiration in living organisms.
- Carbon (C): Found in all living organisms and used in various forms like graphite and diamonds.
- Sulfur (S): Used in fertilizers and some industrial processes.
3. Metalloids
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Characteristics:
- Have properties of both metals and nonmetals
- Semi-conductors (partially conduct electricity)
- Can be shiny or dull
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Examples:
- Silicon (Si): Used in computer chips and solar panels.
- Boron (B): Used in glass and detergents.
- Arsenic (As): Used in some alloys and semiconductors.
Summary Table
| Category | Characteristics | Example Elements | |------------|------------------------------------------|-------------------| | Metals | Good conductors, shiny, malleable | Iron (Fe), Copper (Cu), Gold (Au) | | Nonmetals | Poor conductors, dull, brittle | Oxygen (O), Carbon (C), Sulfur (S) | | Metalloids | Semi-conductors, properties of both | Silicon (Si), Boron (B), Arsenic (As) |
This classification helps in understanding the properties and applications of different elements in science and everyday life.