Elements, Compounds and Mixtures Flashcards
Element:
- Substances that cannot be broken down into anything simpler
- Anelementis a substance made from only one type of atom
- This means that it cannot be broken down into two or more simple substances by means of a chemical reaction
Description of an elements in terms of arrangement of atoms:
- Elements are made up only one type of atom
- these atoms can exist as individual atoms e.g. Ne or bonded to other atoms of the same element to form molecule e.g. O2
- monatomic, diatomic, etc.
- giant aggregates egs
Compound:
- Substances which contain atoms of two or more elements which are chemically bonded in a fixed ratio/proportion
- The elements in a compound are in a fixed ration which is shown by the formula e.g. in the compound of water (formula = H2O) there are two atoms of hydrogen for every 1 atom of oxygen
Describe compounds in terms of arrangement of atoms:
- The elements is a compound are difficult to separate and need to undergo a chemical change if this is to happen.
- arranged in a fixed ratio
Mixture:
Substances which contain two or more elements OR compounds in the same place in a variable ration and which are not chemically bonded.
Describe mixtures in terms of arrangement of atoms:
The different particles in a mixture are not chemically bonded together and so can be separated from each other with relative ease.
What three things do you need for a fire?
oxygen, heat, fuel
What % of the air is made up of oxygen?
20-21%
What % of the air is trying to put out a fire?
80-79% e.g. CO2, N, Argon - unreactive gases
Melting and Boiling Points of Non-Metals:
- low melting point
- low boiling point
What two classes are elements divided into?
metals and non-metals
How many elements occur naturally?
- There are 92 different types of atoms that occur naturally - so there are92natural elements
Examples of compounds:
- Hydrogen and oxygen combine to formwater
- Water is a compound. It is not easy to separate water intohydrogen andoxygen
- Sodium and chlorine combine to formsodium chloride orsalt
- Salt is a compound
What are the differences between compounds and mixture?
- Compounds: proportions of elements are fixed / Mixtures: proportions of the different substances vary
- Compounds: properties different from those of elements used to make the compound / Mixtures: Properties are those of the separate substances in the mixture
- Compounds: cannot be separated into elements without a chemical reaction / Mixtures: can be separated by a physical change (E.g. dissolving one of the substances) or by a simple method (E.g. using a magnet to separate iron)
- Compounds: there is usually a significant energy change when a compound is made from its elements / Mixtures: there is usually no significant energy change when substances are mixed
Examples of mixtures:
- Salt dissolves in water to formsalt solution
- This is an example of amixture
- When salt solution is heated, or left for some time, thewaterevaporates leaving thesalt
- So this mixture can beseparatedagain fairly easily
