In my recent sessions with both Sec 3 and 4 Chemistry Weekly Classes, i realised that Chemical Bondings is one of the key basic topic that many students are having problems in understanding and scoring in their Chemistry tests & exams.
Chemical Bondings comprise of the following sub-topics:
- Ionic Bonding
- Covalent Bonding
- Metallic Bonding (not in Combine Science syllabus)
and examiners will be looking out for specific keywords from students.
There is this tendency that students used the wrong keywords associated with one type of bonding for another type, or miss out on keywords to score the grades they truly deserve in this basic Chemistry topic.
Let’s take a look at one of the exercises that i have recently gave to my Sec 4 GCE-O Level Chemistry Class.
Example 1: Student A
Remarks:
For Part (a)
1. Student do not know what to write in order to obtain the 2 marks in Part (a) of the question. He actually wrote a few lines of redundant information in which the examiners will not give him any marks for.
2. He will get 1 mark for mentioning that ions are held together by strong electrostatic forces of attraction which requires a large amount of energy to overcome.
3. However, he missed out on the other set of keywords that examiners are looking out for, which is: “Crystal Lattice Structure”. Other accepted keywords are “Giant Ionic Structure” or “Giant Lattice Structure”.
For Part (c):
1. We do not usually mention bonds in Ionic Compound. Instead, we should always give the answer with keywords such as “electrostatic forces of attraction between the ions”. This is what examiners are looking out for.
NOTE:
Chemistry students
– you need to know how your examiners / teachers mark your answers. You need to know what they want!
They have hundreds, if not tens of thousands of scripts to mark. As such, do not expect them to read your answer slowly and carefully, and award you marks for anything you write that may sound true.
In fact, they have an “Answer Script” that they follow very very very closely. For the above question of Part (a),? their “Answer Script” may just shows the following answers:
- “Ions are held by strong electrostatic forces of attraction” (1 mark)
- “Held in Crystal Lattice Structure” (1 mark)
As such, when they screen through your answer script and see the two sets of keywords, they will generally award you the full 2 marks – of course your answer must not be phrased until it’s out of point (or with redundancy).
Know What Examiners Want In Your Answer:
Do a search on archive blogposts that i have shared in last 3 years on Common Errors made by Chemistry Students.
If you have been studying very hard but just can’t seemed to score full marks for each question, you can check out Up Your Chemistry Grades Now – a Chemistry Critical Guidebook that i have written 2 years ago that address:
- What Examiners Want In Your Answer
- Common Mistakes Made by Students Year-after-Year
PS: Grab a f-r-e-e introductory copy of Up Your Chemistry Grades Now by Clicking HERE
Calcium ion (+2) has a higher charge than sodium ion (+1). Thus calcium chloride has a stronger ionic bond than sodium chloride. Hence calcium chloride has a higher melting point than sodium chloride.
I agree with varda above . shouldn’t it be NACL since the mole ratio between the ions are 1:1 whereas in cacl2 its 1:2 , therefore nacl has stronger electrostatic force between the ions ??? please get back to me asap coz I’ve got a little confusion there . cheers .
electrostatic forces of attraction (EFA) is the Keyword, i presume ?
Please tell me answer of part c)…i dont get it.shouldn’t it be that in Nacl only 1 electron is transffered and gained whereas in CaCl2 2 electrons are transffered and gained which makes a stronger ionic bond?