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14 Cards in this Set
- Front
- Back
What is an element? |
element is a pure substance that cannot be broken down into two or more simpler substances |
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How are elements classified? |
1) Whether they have metallic, metalloid or non-metallic properties 2) Physical states (at room temperature and pressure - gases, liquids or solid |
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Properties of metals |
Appearance: shiny (lustrous) physical state at r.t.p. : mostly solid (except mercury) melting and boiling points: high (except sodium, potassium and mercury) Ductility and malleability: Ductile (can be drawn into wires) malleable (can be hammered into different shapes without breaking) sonorous (make a ringing sound when struck) Heat conductivity: good electrical conductivity: good |
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Properties of metalloids |
Appearance: shiny (lustrous) Physical state in r.t.p.: solids Melting and boiling points: high ductility and malleability : brittle (easily broken when hammered) heat conductivity: moderate electrical conductivity Moderate |
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Properties of non-metals |
Appearance: dull (non-lustrous) physical state at r.t.p. Gases, volatile liquids (easily evaporated) or solid Melting and boiling points: low (except for carbon and silicon) Ductility and malleability: brittle if solid Heat conductivity: poor(except carbon in the form of graphite and diamond) |
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Atoms and molecules
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Atoms meaning: smallest particles of an element that have the chemical properties of that element Monatomic elements: element contains only one type of atom e.g. helium, neon, argon, krypton, xenon and radon Molecules: a group of 2 or more atoms that are chemically combined Diatomic molecules: made up of two atoms Polyatomic molecules: made up of three or more atoms |
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Meaning of compound |
A pure substance containing two or more elements that are chemically combined in a fixed ratio |
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What are compounds made up of |
Can be made up of molecules or ions (electrically charged particles. An ion carries either positive or negative charges) |
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Does a compound have the same properties as the elements that form it? |
A compound has different properties from the elements that form it. |
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Chemical formula of a compound |
The chemical formula of a compound is written by putting together the chemical symbols of the elements that make up the compound Chemical formula tells us: The types of atoms present in the compound The ratio of the different atoms present in the compound |
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Decomposition of Compounds |
Chemical processes such as thermal decomposition and electrolysis can be used to decompose compounds (break down compounds into elements or simpler compounds). |
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Thermal decomposition and electrolysis meaning |
Thermal decomposition involves heating a compound strongly. E.g. mercury (II) oxide is heated strongly, it decomposes to give the elements mercury and oxygen Electrolysis uses electricity to break down the compound |
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Mixture |
made up of two or more substances that are not chemically combined |
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Mixture vs compound |
Mixture is formed when we add sulfur powder to iron filings Separation: The components of a mixture can be separated by physical processes such as magnetic separation, filtration or distillation. Properties: The chemical properties of a mixture are the same as those to its components Energy change: No chemical reaction takes place when a mixture is formed - usually there is little or no energy chance Composition: The components of a mixture can be mixed in any ratio Compound: When the mixture is heated, the mixture glows and a black solid , iron(II) sulfide, is obtained. Iron(II) sulfide is a compound of two elements, iron and sulfur Separation: A compound can only be broken down into its elements or into simpler compounds by chemical processes (e.g. thermal decomposition or electrolysis) Properties: The physical and chemical properties of a compound are different from those of its constituent elements energy change: A chemical reaction takes place when a compound is formed - usually there is an energy change e.g. the reactants get hot or cold Composition: The elements in a compound are always combined in a fixed ratio |