Elements, Compounds, Mixtures Flashcards
what are elements?
A substance made of only one type of atom.
There are about one hundred different elements, their names are found on the periodic table.
what are compounds?
a substance made from two or more different elements that have been chemically joined.
Examples of compounds include water (H2O), which is made from the elements hydrogen and oxygen, and table salt (NaCl), which is made from the elements sodium and chloride.
The elements in a compound cannot be separated by physical means (e.g. filtration, evaporation, distillation) because the elements chemically bonded together
what are mixtures?
Elements and/or compounds mixed by NOT joined together. Mixtures can be easily separated by physical means (e.g. filtration, evaporation, distillation) because the different elements and/or compounds are not joined together
what are the differences between elements, compounds and mixtures in terms of atoms and molecules they are made of?
Elements are made up of only one type of atom and are represented my the same type of atoms / molecules which are made of atoms.
Compounds are substances made of two or more different elements with different types of atoms and molecules joined together.
Mixtures are elements and/or compounds mixed together but not joined together and is represented with a variety of different atoms and molecules from different elements and compounds.
what is this: element, compound or mixture?
compound
what is this: element, compound or mixture?
mixture
what is this: element, compound or mixture?
element - same type of atoms
what are separation techniques?
A separation technique is used to separate mixtures (sieving, filtration, evaporation etc.).
why do separation techniques work?
Separation techniques work because the different substances in the mixture are not joined together and have different properties e.g. different sized pieces, different boiling points or different solubilities.
sieving…
A separation technique used to separate large pieces of solid from small pieces of solid.
The small pieces can fit through the holes in the sieve, the large pieces cannot so get trapped.
separating funnel…
Used to separate liquids that do not dissolve into one another so form layers (e.g. oil and water).
Oil cannot dissolve in water so the mixture has two layers. The oil is less dense than water so floats on top. The water is run out of the bottom of the separating funnel using the tap. When all the water has been let out, the tap is closed so that the oil stays in the funnel.
magnetism…
Magnetism can be used to separate a magnetic substance (e.g. iron) from a non-magnetic substance.
The magnetic substance will be attracted to the magnet but the non-magnetic substance will not.
filtration…
A separation technique used to separate an insoluble solid from a liquid, e.g. sand from water.
The filter paper has tiny holes in it, the liquid particles can fit through the holes but the solid particles cannot so get trapped in the filter paper.
evaporation…
A separation technique used to separate a soluble solid from the liquid it is dissolved in, e.g. salt from salt solution. It can also be called crystallisation, because crystals are formed
The water (or other solvent) evaporates leaving the soluble solid behind as crystals. Heating will speed the process up. The crystals do not evaporate because they have a very high boiling point (over 1000°C).
chromatography…
A separation technique used to separate mixtures of colours, e.g. food colouring or ink.
The colours dissolve in the water (or other solvent) and travel up the chromatography paper. Different colours are separated because they have different solubilities so travel different heights up the chromatography paper. The more soluble a colour is the further it will travel.
The paper with coloured spots on that is made in chromatography is called a chromatogram. The number of spots tells us how many colours the original mixture contained. Identical colours travel the same height up the paper.
For example:
distillation…
A separation technique used to separate either:
- Pure water from impure water e.g. salt solution (water with salt dissolved in it) or tap water (which has minerals dissolved in it).
* The water evaporates at its boiling point (100°C), it cools in the condenser and condenses back to liquid.
* The impurities (salt, minerals etc.) have a very high boiling point (higher than a Bunsen burner can reach) so stay in the flask. - Liquids that dissolve into one another e.g. ethanol (alcohol) and water.
* The different liquids have different boiling points so will evaporate at different temperatures.
* The liquid with the lowest boiling point (e.g. ethanol, 78°C) evaporates first, it cools and condenses in the condenser and is collected.
* When all of this liquid has evaporated the temperature rises and the next liquid starts to evaporate (e.g. water, 100°C), it cools, condenses and is collected in a different container.
what is a molecule?
A small group of non-metal atoms bonded together. We can have molecules of elements - all the atoms would be the same type.
Molecules can also be compounds - different types of atoms bonded together.
monatomic…
A substance made from atoms that exist on their own (individual atoms) – this is how the atoms are arranged for all the group 0 elements, e.g. helium, neon and argon. ‘mon’ = one, ‘atomic’ = atom
diatomic…
A molecule made from two atoms joined together (paired atoms) – this is how the atoms are arranged for all the elements that are gases at room temperature except group 0 elements, e.g. oxygen (O2), hydrogen (H2) and nitrogen (N2). ‘di’ = two, ‘atomic’ = atoms
what is the periodic table.
The periodic table, also known as the periodic table of the elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of chemistry.
group…
A vertical column on the periodic table, e.g. group 1 contains the elements lithium, sodium, potassium, caesium and francium.
Elements in the same group on the periodic table do similar chemical reactions.
period…
A horizontal row on the periodic table, e.g. period 2 contains the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon.
