chemistry presentation icse class IX competition

Chemistry presentation ICSE Class IX

1. Chemistry Language Of chemistry

2. What is a symbol? A symbol is a short form or an abbreviation of an element which displays it and also shows the atomic weight Such as Na for Natrium(Sodium) This system was developed by Berzelius in 1814

3. Valency It is the number of hydrogen atoms which can combine with an atom of the element Variable valency is when an element has more than one valency ex – Cu = 1+ and 2+ , Pt = 2+ and 4+ Fe = 2+ and 3+

4. Valency chart

5. Radicals They are a group of atoms that behave like a single unit and show valency Positive Radical – NH4 1+ Negative Radical – OH 1-

6. Compound It is a pure substance It cannot hold the properties of the original element thus they have different properties It is always homogeneous It is always in a definite proportion Ex – NaCl(common salt)

7. How to write the chemical formula? Na (1+) Cl (1-) 1 1 Since both of their valency is 1 they cancel each other out = NaCl They interchange their valencies