Elements and Compounds(元素與化合物)

1、Elements and Compounds(元素與化合物)Relative (相對(duì)) abundance (豐度) of different elementsDifferences between compound (化合物) and mixture (混合物)Some definitions (定義)nElement (元素) e.g. hydrogen, oxygen A pure substance containing one kind of atoms only.nCompound (化合物) e.g. water, sodium chlorideA pure substance

2、in which more than one kinds of atoms are chemically combined together.nMixture (混合物) e.g. sea water An impure substance with more than one element or compound mixed together.Relative abundance (豐度) of different elements on the earths crust (地殼)List the 4 most abundant (豐富的) elements on the earths c

3、rust in order of decreasing abundance (豐度).List the 4 most abundant (豐富的) elements on the earths crust in order of decreasing abundance (豐度).nOxygen, Silicon, Aluminium, IronRelative abundance of different elements in the universeWhich are the most plentiful (豐富的) substances containing silicon and o

4、xygen respectively on the earths crust ?Which are the most plentiful (豐富的) substances containing silicon and oxygen respectively on the earths crust ?nCommon nameRock, sand, quartznChemical nameSilicon(IV) oxide, silicon dioxidenFormulaSiO2(s)Difference between Compound and Mixture of elementsDiffer

5、ences between iron(II) sulphide and iron/sulphur mixtureDifferences between iron(II) sulphide and iron/sulphur mixtureiron(II) sulphideiron/sulphur mixtureAppearance (外觀)Formation (形成)Magnetic (磁力的) propertiesReaction with acidAction of waterDifferences between iron(II) sulphide and iron/sulphur mix

6、tureiron(II) sulphideiron/sulphur mixtureAppearance (外觀)black solidGrey powder and yellow powder mixedFormation (形成)Heat evolvesNo heat changeMagnetic (磁力的) propertiesNon-magneticIron powder remains magnetic while sulphur powder remains non-magneticReaction with acidA colourless gas with bad egg sme

7、ll evolvesAn odorless, colourless evolves which burns with a pop soundAction of waterJust sinkGrey powders sink, Yellow powders floatStructural (結(jié)構(gòu)上的) difference between mixture and compoundDifferences between carbon dioxide and oxygen/carbon mixtureDifferences between carbon dioxide and oxygen/carb

8、on mixturecarbon dioxidecarbon/oxygen mixtureAppearance (外觀)Formation (形成)AcidityAction of limewater(石灰水)Differences between carbon dioxide and oxygen/carbon mixturecarbon dioxidecarbon/oxygen mixtureAppearance (外觀)A colourless gasA colourless gasFormation (形成)Heat evolvesNo heat changeAcidityAcidic

9、NeutralAction of limewater(石灰水)Turns limewater milkyLimewater remains colourlessStructural (結(jié)構(gòu)上的) difference between mixture and compoundmixture of carbonand oxygencompound ofcarbon dioxideDifferences between compound and mixture CompoundsMixture of elementsComposition(成份成份)constant compositione.g.

10、in water (H2O), the ratio of H atom to O atom is 2 to 1. variable composition (no formula can be assigned.)e.g. different stainless steels contain different amounts of iron and carbon. Composition by massconstant compositione.g. in water, the mass of H atom to O atom is 1 : 16 and the number ratio i

11、s 2 : 1, therefore, the mass of hydrogen to oxygen in water would always be 1 : 8. variable (可變的) composition Melting pointa sharp melting point because it is pure. a wide melting range because it is not pure. Separation of constituentsconstituents can only be separated by chemical method (e.g. elec

12、trolysis) constituents can be separated by physical method (e.g. distillation, filtration) Heat change of formationusually heat is evolved or absorbed upon formation no heat change involved. Propertiesproperties of the compound is so different from the constituent elements individual elements retain

13、 (保持) their own properties. What is the formula of water ? What is the formula of sea water ? What is the formula of water ? What is the formula of sea water ?nWater - H2OnSea water - no formula, only pure substances can have formulasWhich of the followings is most plentiful in the nature, pure elements, compounds or mixtures ?Which of the