Lower Secondary Science
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Thanks a lot for sharing, Dr. Daniel.
May I say that the mentioned 3 books Physics Matter, Biology Matter and Chemistry Matter are meant for students taking pure phy, bio and chem O level?
These books may be too tough for my sec 1 girl and thus am hesitating buying them though listed in the booklist. -
Yes the books mentioned above are meant for Pure Physics, Chem etc. The one I have seen used for the combined science (O-Level) is Discover Physics.
Best thing for starting out in Sec 1 is building a strong foundation on the early Physics and Chem topics. Make sure she knows the metric system well, can convert meters to kilometers to milimeters etc. Then can convert speeds of meters/second to kilometers/hour etc. In chemistry basic knowledge of elements and compounds and the basic structure of the atom is a good place to start. -
Ds has a chemistry question…
He said he knows how to get valency of simple ions - like potassium K has a valency of 1+ due to its electronic configuration of 2.8.1 hence need to get rid of 1 electron.
But he doesn’t know how the valency of polyatomic ions like CO3 and NH3, etc are derived. In my sec sch days, I just memorized the valencies of these polyatomic ions. Now when my ds asks me, I don’t know how to explain.
Anyone can help to explain? -
Verysuperkiasu:
The bonds in CO2 are covalent ie the electrons are shared and not transferred..Ds has a chemistry question.....
He said he knows how to get valency of simple ions - like potassium K has a valency of 1+ due to its electronic configuration of 2.8.1 hence need to get rid of 1 electron.
But he doesn't know how the valency of polyatomic ions like CO3 and NH3, etc are derived. In my sec sch days, I just memorized the valencies of these polyatomic ions. Now when my ds asks me, I don't know how to explain.
Anyone can help to explain? -
Belle2011:
Exactly..the bonds in NH3, CO2, O2 molecules are covalent bonds, unlike simple ions, where electrons get transferred to, or transferred from. So how do we arrive at the conclusion that valency of NH3 is 1-, SO4 is 2- ?
The bonds in CO2 are covalent ie the electrons are shared and not transferred..Verysuperkiasu:
Ds has a chemistry question.....
He said he knows how to get valency of simple ions - like potassium K has a valency of 1+ due to its electronic configuration of 2.8.1 hence need to get rid of 1 electron.
But he doesn't know how the valency of polyatomic ions like CO3 and NH3, etc are derived. In my sec sch days, I just memorized the valencies of these polyatomic ions. Now when my ds asks me, I don't know how to explain.
Anyone can help to explain? -
Verysuperkiasu:
Sometimes the easiest thing is to memorize the charges on these ions, for quick recollection. But it is logical how they form and its good to be able to understand this. Here is an explanation.Ds has a chemistry question.....
He said he knows how to get valency of simple ions - like potassium K has a valency of 1+ due to its electronic configuration of 2.8.1 hence need to get rid of 1 electron.
But he doesn't know how the valency of polyatomic ions like CO3 and NH3, etc are derived. In my sec sch days, I just memorized the valencies of these polyatomic ions. Now when my ds asks me, I don't know how to explain.
Anyone can help to explain?
See if he can make sense out of why the CO2 molecule forms. Carbon has 4 valence electrons and would like to share 4 more to get to 8. Each Oxygen has 6 valence electrons and would like to share 2 more to get to 8. So when the Carbon shares 2 electrons with each oxygen everybody is happy, they all have 8.
Now Carbonate or CO3 has a third oxygen atom. This third Oxygen atom needs to find two more electrons to get to a valency of 8. So what happens is the CO3 molecule can steal 2 electrons from another source to compensate for the need of the third Oxygen atom to have two more electrons. When it does this it becomes CO3 with a 2- charge.
For Nitrate or NO3, the Nitrogen has one more valence electron than Carbon, so NO3 needs to steal one less electron so that all the atoms in the molecule have 8 shared electrons. So the NO3 ion has a -1 charge.
Another easy one to understand is OH- or Hydroxide. Oxygen has 6 valence electrons and would like to share two more to get to 8. So H2O is formed for that reason. The Oxygen shares one electron from each Hydrogen. With only one hydrogen attached to an Oxygen, the molecule steals one more electron, so it becomes OH with a -1 charge.
The understanding of Sulfate and Phosphate is a bit more difficult, but if you follow similar logic you will get there. -
Ah…so! Now I see it. Will try to explain this to my ds. Thanks so much, Dr Daniel, for your comprehensive and detailed explanation. Really appreciate that!!
Just one more question…Carbon has an a valence electron of 4. So, can we say carbon is only found in covalent molecules? That is, it can’t transfer electrons like metals can to form positive ions? And carbon can only share electrons, right? -
Carbon mostly forms covalent bonds. The terms covalent and ionic really are relative terms. Most bonds are somewhere in between equal sharing of electrons between two atoms and electrons completely taken from one atom. Later on in chemistry they will introduce the concept of electronegativity which gets into the degree to which an atom or molecule attracts electrons to itself.
But in chemistry you do sometimes see carbon involved in ionic bonding. The compound Calcium Carbide or CaC2 is usually described as having ionic bonds within it.
But the main point about Carbon that is usually stressed in Lower Secondary is that it is very well suited to form covalent bonds because it has exactly half of the 8 valence electrons. Atoms that have one extra electron have a strong desire to give one away. Atoms that are one short have a strong desire to gain one. Carbon and Silicon, in the middle, are best suited for sharing electrons.
Happy NEW YEAR !! - Hope everyone has a good 2012 !
We can toast the new year with C2H6O -
Dr.Daniel:
:thankyou:
But the main point about Carbon that is usually stressed in Lower Secondary is that it is very well suited to form covalent bonds because it has exactly half of the 8 valence electrons. Atoms that have one extra electron have a strong desire to give one away. Atoms that are one short have a strong desire to gain one. Carbon and Silicon, in the middle, are best suited for sharing electrons.
Happy NEW YEAR !! - Hope everyone has a good 2012 !
We can toast the new year with C2H6O
Happy a great year ahead too.. :rahrah: -
My DS has a physics question. It is on the topic of light.
Converging lens A & B have the same focal length, but B is only half the diameter of A. Both lenses are used to form the images of distant objects on a screen. Which of the statement is correct?
A. For both lenses, the distances from the lens to the screen is the same.
B. For both lenses, the images are of the same brightness.
C. For both lenses, the images are the same size as the object.
D. Lens B gives a smaller image than A.
The correct answer is C, but my DS still do not understand. May anyone enlighten us?
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