Define an element
An element is a pure substance that cannot be broken down into 2 or more simpler substances by chemical processes (e.g heating/ electrolysis)
How to classify elements?
Category 1:
- Metals
- Non-metals
- Metalloids
Category 2: (Physical states)
- Gases
- Liquids
- Solids
What are the metallic properties of elements (aka the metallic categories for classification)
- Appearance
- Physical state at r.t.p
- m.p & b.p
- Ductility and malleability
- Heat conductivity
- Electrical conductivity
Describe the following for metals:
- Appearance
- Physical state at r.t.p
- m.p & b.p
- Ductility and malleability
- Heat conductivity
- Electrical conductivity
- Shiny (lustrous)
- Mostly solid (except for Mercury, at r.t.p)
- High (except for potassium and Mercury)
- Ductile (can be drawn into wires), malleable (can be hammered into diff shapes without breaking), sonorous (makes a ringing sound when struck)
5 & 6. Good
Describe the following for non-metals:
- Appearance
- Physical state at r.t.p
- m.p & b.p
- Ductility and malleability
- Heat conductivity
- Electrical conductivity
- Dull (non-lustrous)
- Gaseous, volatile (can evaporate easily) liquids, solids
- Low (except silicone and carbon)
- Brittle if solid
5 & 6. Poor (except carbon and graphite)
Describe the following for metalloids:
- Appearance
- Physical state at r.t.p
- m.p & b.p
- Ductility and malleability
- Heat conductivity
- Electrical conductivity
- Shiny (lustrous)
- Solid
- High (except for potassium and Mercury)
- Brittle (easily broken when hammered)
5 & 6. Moderate
How to confirm identity and/ or purity of an element
m.p and b.p
[Note: impurities lowers m.p but higher b.p]
Define atoms
Atoms are the smallest particles of an element that have the chemical properties of that element
Define molecules
A molecule is a group of 2 or more atoms that are chemically combined
Define monoatomic elements
An element that can exist as one individual atom (aka noble gases)
What are diatomic/ polyatomic molecules
Diatomic - Formed by a combination of 2 atoms
Polyatomic - 3 or more atoms combined
Define a compound
A compound is a pure substance containing 2 OR MORE elements that are CHEMICALLY COMBINED in a FIXED RATIO, and can be present in the form of molecules and ions
(e.g Water)
What can a chemical formula tell us about a compound?
- Types of atoms present
- RATIO of diff atoms present
What is thermal decomposition
Thermal decomposition involves heating a compound strongly to break down the compound into elements
Define a mixture
A mixture is made up of 2 OR MORE substances that are NOT chemically combines
[Note: Ratio of components are not fixed in a mixture]
The diff between compounds and mixtures (categories)
- Separation
- Properties
- Energy change
- Composition
How are mixtures and compound different in terms of separation?
Mixture:
The components can be separated by physical processes such as magnetic separation, filtration or distillation
Compound:
It can only be broken down into its elements or into simpler compounds by chemical processes (e.g thermal decomposition or electrolysis)
How are mixtures and compound different in terms of properties?
Mixture:
Chemical properties of a mixture are the same as those of its components
Compounds:
The physical and chemical properties of a compound are different from those of its constituent components
How are mixtures and compound different in terms of energy change?
Mixture:
No chemical reaction take place when a mixture us formed – Usually there is little or no energy change
Compounds:
A chemical reaction takes place when a compound is formed – usually there is an energy change (e.g the reactants get hot/ cold)
How are mixtures and compound different in terms of composition?
Mixture:
The components can be mixed in any proportion
Compounds:
The elements in a compound are always combined in a fixed proportion
4 facts about alloys
- it a mixture
- May contain a non metal
- The chemical properties of an alloy ARE similar to the elements that form it
