Chemistry - Valence and Chemical Formulae

19,379 views

Published on

This presentation will discuss on valencies and how to deduce the chemical formulae of a pure substance.

Published in: Education, Technology, Business
0 Comments
3 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
19,379
On SlideShare
0
From Embeds
0
Number of Embeds
8
Actions
Shares
0
Downloads
356
Comments
0
Likes
3
Embeds 0
No embeds

No notes for slide
  • Examples of organic acids
  • Examples of organic acids
  • Examples of organic acids
  • Examples of organic acids
  • Chemistry - Valence and Chemical Formulae

    1. 1. This presentation was produced by the Sciencedepartment of Temasek Secondary School.Redistribution or reproduction of this resource isprohibited by copyright regulations. Thisresource should be used for educationalpurposes.
    2. 2. Acids and AlkalisValency & Chemical Formulae
    3. 3. Today’s Lesson The Meaning of Valency Naming Compounds Writing Chemical Formula
    4. 4. Valency Elements react in order to achieve noble gaselectronic configuration. E.g. chlorine with an electronic configuration of 2.8.7gains one electron to achieve an electronicconfiguration of 2.8.8.
    5. 5. Valency To write the chemical formula of a compound, we mustknow the valency of the elements or ions involved. Valency is the number of electrons that an atomneeds to gain or lose in order to achieve noble gaselectronic configuration. E.g. chlorine has a valency of 1, as it needs to gain 1electron to achieve noble gas electronic configuration.
    6. 6. GroupnumberElementElectronicstructureNo of electrons to gain or lose to achievethe noble gas electronic configurationIon formed ValencyI Li 2.1 Lose 1 electron Li+1I Na 2.8.1 Lose 1 electron Na+1I K 2.8.8.1 Lose 1 electron K+1II Be 2.2 Lose 2 electrons Be2+2II Mg 2.8.2 Lose 2 electrons Mg2+2
    7. 7. GroupnumberElementElectronicstructureNo of electrons to gain or lose to achievethe noble gas electronic configurationIon formed ValencyII Ca 2.8.8.2 Lose 2 electrons Ca2+2III B 2.3 Lose 3 electrons B3+3III Al 2.8.3 Lose 3 electrons Al3+3V N 2.5 Gain 3 electrons N3-3V P 2.8.5 Gain 3 electrons P3-3
    8. 8. GroupnumberElementElectronicstructureNo of electrons to gain or lose to achievethe noble gas electronic configurationIon formed ValencyVI O2.6 Gain 2 electronsO2- 2VI S 2.8.6 Gain 2 electrons S2-2VII F2.7 Gain 1 electronF- 1VII Cl 2.8.7 Gain 1 electron Cl-1
    9. 9. Polyatomic Ions There are some ions that are made up of more thanone atom. They are called polyatomic ions.Some common polyatomic ionsPositive Ion Valency Negative Ion ValencyAmmonium ion, NH4+1 Nitrate ion, NO3-1Hydroxide ion, OH-1Carbonate ion, CO32-2Sulfate ion, SO42-2
    10. 10. Chemical Formula The chemical formula of a substance shows the numberof atoms and the elements that make up the compound.CompoundChemicalformulaNumber of atoms and elementsSodium hydroxide NaOH 1 Na, 1 O and 1 H atomsCopper sulfate CuSO4 1 Cu, 1 S and 4 O atomsAmmonia gas NH3 1 N and 3 H atomsCalcium carbonate CaCO3 1 Ca, 1 C and 3 O atomsAluminium fluoride AlF3 1 Al and 3 F atoms
    11. 11. Naming CompoundsWhen naming an ionic compound that contains onlytwo elements:Metallic element comes before non-metallic elementNon-metallic elements end with ‘ide’
    12. 12. Naming CompoundsElements in an ionic compound Chemical nameCalcium, chlorineCalcium chloride(metal) (non-metal)Lithium, fluorine Lithium fluorideMagnesium, oxygen Magnesium oxidePotassium, sulfur Potassium sulfide
    13. 13. Naming Compounds A polyatomic ion will not change its name aftercombining with other elements.Examples: Sodium carbonate Potassium sulfate Calcium hydroxide Ammonium chloride
    14. 14. Your turn to practise!
    15. 15. ActivityChemical formula of compounds containing the followingsymbols/ groups are called:Ion Name ExampleF-fluoride LiF, lithium fluorideCl-chloride NaCl, sodium chlorideBr-bromide KBr, potassium bromideI-iodide MgI2, magnesium iodide
    16. 16. ActivityChemical formula of compounds containing the followingsymbols/ groups are called:Ion Name ExampleO2-oxide MgO, magnesium oxideN3-nitride Na3N, sodium nitrideP3-phosphide K3P, potassium phosphideNH4+ammonium NH4Cl, ammonium chloride
    17. 17. ActivityChemical formula of compounds containing the followingsymbols/ groups are called:Ion Name Example OH- hydroxide KOH, potassium hydroxide NO3- nitrate NaNO3, sodium nitrate CO32- carbonate MgCO3, magnesium carbonate SO42- sulfate K2SO4, potassium sulfate PO43-phosphate Na3PO4, sodium phosphate
    18. 18. Writing Chemical FormulaExample 1: Sodium chloride             Steps Sodium chloride123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.Na Cl1 1Attach the valency as a subscript.Na1Cl1Simplify the formula.NaCl
    19. 19. Writing Chemical FormulaExample 2: Zinc chloride             Steps Zinc chloride123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.Zn Cl2 1Attach the valency as a subscript.Zn1Cl2Simplify the formula.ZnCl2
    20. 20. Writing Chemical FormulaExample 3: Aluminium oxide             Steps Aluminium oxide123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.Al O3 2Attach the valency as a subscript.Al2O3Simplify the formula.Al2O3
    21. 21. Writing Chemical FormulaExample 4: Magnesium oxide             Steps Magnesium oxide123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.Mg O2 2Attach the valency as a subscript.Mg2O2Simplify the formula.MgO
    22. 22. Writing Chemical FormulaTAKE NOTE when simplifying chemical formulae:The subscript ‘1’ must be omittedReduce the ratio by a common factor if possible
    23. 23. Complete Exercise 1
    24. 24. Writing Chemical Formula For compounds that contain polyatomic ions, a bracketmust be used if a number is required.
    25. 25. Writing Chemical FormulaExample 5: CalciumnitrateSteps Calcium nitrate123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.Ca NO32 1Attach the valency as a subscript.Ca1(NO3)2Simplify the formula.Ca(NO3)2
    26. 26. Writing Chemical FormulaExample 6: SodiumcarbonateSteps Sodium carbonate123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.Na CO31 2Attach the valency as a subscript.Na2(CO3)1Simplify the formula.Na2CO3
    27. 27. Writing Chemical FormulaExample 7: AluminiumsulfateSteps Aluminium sulfate123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.Al SO43 2Attach the valency as a subscript.Al2(SO4)3Simplify the formula.Al2(SO4)3
    28. 28. Writing Chemical FormulaExample 8: AmmoniumchlorideSteps Ammonium chloride123Write the symbols of the elements, theirrespective valencies below the symbols,and criss-cross.NH4 Cl1 1Attach the valency as a subscript.(NH4)1Cl1Simplify the formula.NH4Cl
    29. 29. CompleteExercise 2

    ×