Presentation on theme: "WRITING FORMULA FOR IONIC COMPOUNDS"— Presentation transcript:
1 WRITING FORMULA FOR IONIC COMPOUNDS (NH4)3PO4All you need to know about writing formula for Y11 to Y13 Science
2 IONIC COMPOUNDS Ionic compounds are very common. Some examples are common salt (Sodium Chloride) found in the sea and Limestone (Calcium Carbonate)
3 SOME BACKGROUNDIonic compounds form when metal and non-metal atoms react together and form ions.The METALS form POSITIVE ions.The NON-METALS form NEGATIVE ions.There are also COMPLEX IONS formed from more than one atom.
4 POSITIVE IONSThese are formed when atoms lose electrons and become positively charged.The superscript in the symbol tells us the size of the positive charge.Na+ has a positive one charge.Al3+ has a positive three charge
5 Here are some examples of some Positive ions Sodium Na+Magnesium Mg2+Ferric (Iron III) Fe3+Aluminium Al3+Calcium Ca2+Copper Cu2+
6 NEGATIVE IONS These are formed when atoms gain electrons. The superscript tells you the size of the negative charge.Cl- has a negative one charge.O-2 has a negative two charge.
7 COMPLEX IONSThese are groups of atoms made up of more than one type of atom.They may have a positive or negative charge.Some examples are the Ammonium ion (NH4+) and the Carbonate ion (CO32-)
8 To find out the symbol and charge on an ion Look up the symbol and charge on the table of ions on your worksheetUse this to write the formula of the compound using the method described in the following slides
9 TO WRITE THE FORMULA FOR A COMPOUND (eg Sodium Chloride) YOU MUST KNOW THE Positive ion and theNegative ionNa+Cl-
10 THE IMPORTANT THING TO REMEMBER IS….. The total of the charge on the positive ions MUST equal the total of the charge on the negative ions so that they cancel each other out!
11 NOW, Back to Sodium Chloride The Sodium ion (Na+) has a charge of +1The Chloride ion (Cl-) has a charge ofThe charge on the positive ion is exactly equal but opposite to the charge on the negative ion.So one positive ion exactly cancels the charge on a negative ion. The formula is written as NaCl
12 SO NOW……...The charge on the one positive ion (Sodium) is exactly balanced by the size of the charge on the one negative ion (Chloride)NaClNaClThe compound Sodium Chloride is stable like this.
13 Now, try to write the formula for these on your worksheet... Magnesium OxidePotassium ChlorideCalcium OxideZinc OxideCalcium SulfideCopper OxideLead OxideClick the left mouse button when you have finished.
14 Here are the answers... Magnesium Oxide MgO Potassium Chloride KCl Calcium Oxide CaOZinc Oxide ZnOCalcium Sulphide CaSCopper Oxide CuOLead Oxide PbOIf you got 5 or better you are doing well!
15 Now, a more complicated example. Write the formula for Calcium Chloride Look up the formula for the calcium ionLook up the formula for the Chloride ionCl-Ca+2
16 REMEMBER !…..The total of the charge on the positive ions MUST equal the total of the charge on the negative ions so that they cancel each other out!
17 You need two Chloride ions to balance the charge on a Sodium ion Cl-Total charge = -2Ca2+Total charge = +2
18 THIS TIME……...The charge on the one positive ion (Calcium) is exactly balanced by the size of the charge on the two negative ions (Chlorine)The compound Calcium Chloride is stable like this.ClCaClCaCl2
19 How we write the formula for Calcium Chloride There is one calcium ion, this is shown by writing the symbol- CaThere are two Chloride ions, this is shown by writing the symbol for chloride with a subscript ‘2’- Cl2So the symbol for the whole compound Calcium Chloride is CaCl2
20 Try to write the formula for these compounds on your worksheet Sodium oxideMagnesium ChloridePotassium oxideCopper chlorideLead ChlorideSodium Sulfidealuminium ChlorideIron (II) ChlorideIron (III) ChlorideClick the left mouse button when you have finished.
21 And here are the correct answers … Sodium oxide Na2OMagnesium Chloride MgCl2Potassium oxide K2OCopper chloride CuCl2Lead Chloride PbCl2Sodium Sulphide Na2SAluminium Chloride AlCl3Iron (II) Chloride FeCl2Iron (III) Chloride FeCl3If you got 6 or better you are doing well!
22 WRITING FORMULA FOR COMPOUNDS CONTAINING COMPLEX IONS If a compound contains a complex ion writing its formula can be confusing.If a single complex ion is required it is simply written as its symboleg Nitrate NO3-
23 WRITING FORMULA FOR COMPOUNDS CONTAINING COMPLEX IONS If more than one complex ion is required then brackets are put around the whole symbol, then a subscript to indicate the number of ionsIf you need two nitrates: (NO3)2If you need three nitrates: (NO3)3Confused ! It does gets easier with practise.
24 Now here’s an example: Write the formula for Magnesium Nitrate The symbol for the magnesium ion is :The symbol for the Nitrate ion is :Mg+2NO3-
25 You need two Nitrate ions to balance the charge on a Magnesium ion NO3-Total charge = -2Mg2+Total charge = +2
27 Now try these examples on your worksheet Ammonium CarbonateAmmonium SulfateAmmonium PhosphateSodium CarbonateCopper NitrateCalcium Nitratealuminium NitrateClick the left mouse button when you have finished.
28 Here are the correct answers! Ammonium Carbonate (NH4)2CO3Ammonium Sulfate (NH4)2SO4Ammonium Phosphate (NH4)2SO4Sodium Carbonate Na2CO3Copper Nitrate Cu(NO3)2Calcium Nitrate Ca(NO3)2aluminium Nitrate Al(NO3)3If you got 5 or better you are making excellent progress!
29 Sometimes it is not easy to get the charges to balance! An example is aluminium oxide.The charge on the aluminium ion is 3+The charge on the oxide ion is 2-At first glance these do not easily balanceDo it as follows………...
30 You need three oxide ions to balance the charge on two aluminium ions O-2 O-2Total charge = -6Al3+Total charge = +6
31 THIS TIME……...The charge on the two positive ions (aluminium) is exactly balanced by the size of the charge on the three negative ions (Oxygen)The compound Aluminium Oxide is stable like this.OAlOAlOAl2O3
32 Here are some examples to try.. Copper PhosphateIron (III) OxideIron (III) Sulfidealuminium SulfideMagnesium PhosphateCalcium PhosphateClick the left mouse button when you have finished.
33 And here are the answers... Copper Phosphate Cu3(PO4)2Iron (III) Oxide Fe2O3Iron (III) Sulfide Fe2S3aluminium Sulfide Al2S3Magnesium Phosphate Mg3(PO4)2Calcium Phosphate Ca3(PO4)2Did you get them all correct? Well done if you did. Keep trying if you didn’t.