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National 4 Summary NotesElements, Compounds, Mixtures, Atoms and the Periodic TableElementsAlthough there are so many different substances, they are actually made up of a few very basic substances.These basic substances are called elements.An element is a substance made of only one kind of atom.Its atoms are different from the atoms of other elements.Some elements exist as molecules – 2 atoms bonded together.Molecules consisting of 2 atoms are often described as diatomic.Elements existing naturally as diatomic molecules are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine.A diagram of an element could look like this or Uses of ElementsDifferent elements have different properties. This means that different elements have different uses.Gold is used for jewellery because it does not corrode.Helium is used in balloons because it is lighter than air.Chemical SymbolsEach element has a name of its own.Each element has its own symbol.It can be one letter (capital) e.g carbon is CIt can be two letters (first capital, second lower case) e.g. magnesium is MgIt can be two letters based on its latin name e.g. iron is FeSymbols for the elements are found on the Periodic table and in the data poundsWhen atoms of different elements combine together compounds are formed. A compound is a substance formed when two or more elements have chemically joined together.A diagram of a compound could look like this :- see belowMixturesMixturesWhen we put substances together they may or may not react together.If they react together, they form a compound.A mixture is a mix of substances which have not reacted together.A diagram of a mixture could look like this orIt is not easy to separate the elements of a compound from each other because they have combined or joined with each other. The atoms are firmly attached to each other. It is much easier to separate the substances in a mixture because they have not combined with each other. Usually it is possible to separate the substances in a mixture by quite simple means.DissolvingA solid which will dissolve in water is said to be soluble in water.A solid which will not dissolve in water is said to be insoluble in water.A solid substance dissolves in a liquid to form a solution.The solid which dissolves is called the solute.The liquid which does the dissolving is called the solvent.solute + solvent solutionE.g. sugar + water sugar solutionWhen a substance dissolves in a solvent to form a solution, no new substance is formed – solutions are mixtures.Concentration Of SolutionsIf there is not very much solute in the solution, we say that we have a dilute solution.If there is a lot of solute dissolved in the solution, we say that we have a concentrated solution.If there is so much solute dissolved in the solution that no more can dissolve we say that we have a saturated solution.If we add more solute to a saturated solution it will not dissolve. It will simply lie at the bottom of the beaker. Even stirring will not make any more dissolve. The solution can take no more of that solute.Gas TestsGasTest for gasOxygenRelights a glowing splintHydrogenBurns with a popCarbon dioxideTurns lime water milkyMelting and Boiling pointsThe state of an element at room temperature can be determined by looking at the melting and boiling points of the elements on p5 of the data book.If 25oC is below the melting point of the element is a solid.If 25oC is between the melting and boiling points of the element, then the element is a liquid.If 25oC is above the boiling point of the element then the element is a gas.Different Types Of ElementsMetals and Non-metalsElements can be classified as metal or non-metal.MetalsNon-metalsusually shinyusually dullgood conductors ofNOT good conductors ofelectricity and heatelectricity and heatOn the Periodic Table there is a black zig zag line on the chart. This line separates metal elements from non-metal elements. The metals are on the left of the line, the non-metals are on the right. Non metals MetalsSolids, Liquids & GasesElements can be classified as solids, liquids and gases.Natural and Man-made ElementsMost elements occur naturally in the world. A few do not – they did not exist until they were made by scientists. These elements are man-made or synthetic. All the elements with Atomic Number greater than 92 (Uranium) are man-made.Separating MixturesMixtures can usually be separated, sometimes quite easily.Filtration is used to separate a solid from a liquid.Evaporation is used to separate a mixture of a dissolved solid in a liquid.Physical and Chemical ChangesPhysical Change – changing shapemelting boilingChemical Changenew substance producedElements Everything in the world is made up of about 100 simple substances called elements.Elements cannot be made into anything simpler.All the elements are found in the Periodic Table.They are listed in a special way and this allows us to find out about different elements.Elements in the same group of the Periodic Table have similar properties, that is, their chemical behaviour is similar.The alkali metals are group 1 – these are very reactive metalsThe Halogens are group 7 – these are quite reactive non-metals.The Noble Gases are group 0 – these are very unreactive gases.The Transition Metals are the block in the middle – they are not in a group.group 0group 1group 7More About AtomsAll elements have just one kind of atom in them.Atoms are built of three kinds of even smaller particles – protons, electrons and neutrons.NameSymbolChargeMass (amu)protonp+11electrone-11/2000neutronn01Protons are positively charged and found in the nucleus.Neutrons have no charge (neutral) and are found in the nucleus.Electrons are negatively charged and are found outside the nucleus.An atom is neutral overall since the number of positive protons equals the number of negative electrons.Atomic NumberThe Atomic Number of an element tells us the number of protons in the nucleus of its atoms.It is the number of protons that make an element what it is.Since an atom is neutral it also tells us the number of electrons. Atomic number = number of protons = number of electronAtomic NumberThe Atomic Number of an element tells us the number of protons in the nucleus of its atoms.It is the number of protons that make an element what it is.Each element has a different atomic number, therefore each element has a different number of protons in its nucleus.Since an atom is neutral it also tells us the number of electrons. Atomic number = number of protons = number of electrons.Mass NumberThe mass number of an element is the number of protons PLUS neutrons in the nucleus of an atom. Mass number = number of protons + number of neutrons ................
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