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What is the best method to classify a chemical substance?, Bonding -…
What is the best method to classify a chemical substance?
What is a chemical substance
Constant chemical structure
Characteristic properties
Can be elements or compounds
Nature of substance
Structure
Metallic lattice
Metallic bonds
Strong
Solid at room temperature
Giant covalent structures
Made of covalent bonds but very strong with high melting point
Usually non Conductive unless it is graphite
Solid at room temperature
Ionic latttice
Made of ionic bonds
Solid at room temperature
Covalent molecules
Normal covalent bonds
Can be solid, liquid or gas at room temp
Methods
Solubility test
Place substance into water and stir for 30 seconds to see if it is soluble
Eliminates metallic and covalent networks as they are not soluble, and most covalent compounds also have low solubility
Conductivity test
Test substance with conductivity kit in aqueous and solid forms
Eliminates covalent networks and molecules as they are not conductive
Shatter test
Smash it with a hammer and see if it breaks
Eliminates ionic compounds and covalent molecules as they break more easily than metallic compounds and covalent structures
Melting Point test
Place substance into test tube and wave over flame until it melts. Time amount of time it takes.
Eliminates ionic compounds and covalent molecules as they have lower melting points
RIsks
Can burn things and yourself with flame
You could smash a finger while doing the shatter test
If you spill water from the solubility test you could slip and fall
Lighting a match after opening the gas valve could create a fire which can burn you and set things on fire
Limitations
Most of the tests cannot completely rule out some types of structures as there can be exceptions(e.g. graphite)
Tests may be limited due to resources and time constraints might meant that all tests might not be completed
Observation test is limited as the visual elements are usually all quite broad and there are always exceptions
Observation Test
Look at the substance and observe if it has characteristics of metals, covalent molecules or ionic compounds.
Lustre: Usually Metallic
Crystalline Solids: Usually ionic
Dull: Usually Covalent molecules
Can help narrow down all types of substances as it is applicable they all have different visual properties
Bonding
Ionic bonding: Metal and Non-Metal
high melting and boiling points
Soluble in water
Conducts electricity in aqueous and molten forms
Metallic bonding: 2 metals
Magnetic, Conductive of heat and electricity
High melting point and strong
Ductile and malleable
Covalent bonding: 2 non-metals
Low melting and boiling point
Not electrically conductive