Biology; Chemistry; Physics: Post your doubts here!

[♫Prince Shah♫]

This is what i have concluded.

Group 1 consists of ALKALI METALS. They are metals with METALLIC BONDING.
They consist of POSITIVE METAL IONS, surrounded by a sea of de-localized electrons.
Now the attraction between the Positive metal ions and the free-electrons, is what holds the metal together, and this is what Metallic Bonding is.
As we go down the group, the atomic radius increases. Now, the distance of the Positive ions from the free moving electrons will increase, and thus their force of attraction will decrease resulting in a WEAKER METALLIC BONDING. That will mean that less heat energy will be required in order to melt it, so that is why the melting point decreases down the group.

But Group 7, are the Halogens. They are Non-Metals, which form covalent compounds. They exist as Di-atomic molecules, Cl2, Br2, F2 and there are weak inter-molecular forces of attraction between these molecules. Now, as the atomic mass and size increases, the strength of the intermolecular forces increases. So more heat energy is required to overcome these forces of attraction, so the melting point increases down the group.

So in ALKALI METALS, Melting point decreases down the group. In HALOGENS, the melting point increases down the group.

yup, meh above post has same things as uh have in this..

 

[Nabeel.Ahmad]

yup, meh above post has same things as uh have in this..

Yes.

 

[***amd***]

whts so difficult? its all given in ms.

black widow, i mean what do u want me to explain?

 

[funky brat]

Firstly you have to see that this is an example of identical twins being formed because the a single egg is fertilised and the division of zygote occurs later that produces the 2nd embryo. Once you identify this it's easy to answer this question. Since these embryos are formed from the division of the same zygote there are genetic similarities between the two. So they would have the same DNA. Identical twins always have the same sex and blood group.
The changes that could occur between the two adults would be based on the external factors only. One embryo gets greater nourishment due to its position in the uterus while the other gets less. That would also bring a variation in the size and weight of the two.
black widow

 

[black widow]

Firstly you have to see that this is an example of identical twins being formed because the a single egg is fertilised and the division of zygote occurs later that produces the 2nd embryo. Once you identify this it's easy to answer this question. Since these embryos are formed from the division of the same zygote there are genetic similarities between the two. So they would have the same DNA. Identical twins always have the same sex and blood group.
The changes that could occur between the two adults would be based on the external factors only. One embryo gets greater nourishment due to its position in the uterus while the other gets less. That would also bring a variation in the size and weight of the two.
black widow

thnx alot

 

[funky brat]

thnx alot

You are welcome. Biology is something I'm good at so yeah.

 

[♫Prince Shah♫]

You are welcome. Biology is something I'm good at so yeah.

hehehe

 

[Nabeel.Ahmad]

Why does the reactivity increase down the group in Alkali Metals, and decreases down the group in the case of Halogens? :/

 

[♫Prince Shah♫]

Why does the reactivity increase down the group in Alkali Metals, and decreases down the group in the case of Halogens? :/

in case og gp 1:
mportant trends down group 1:

the melting point and boiling point generally decrease
the element gets more reactive

the atoms get bigger (as more electron shells are added)

generally the density increases (although the atom gets bigger, there is greater proportional increase in the atomic mass.

generally the hardness decreases (The bonding in metals involves the attraction between free negative electrons moving between positively ionised metal atoms (M+ ions). As the atomic radius increases the charges are further apart and the electrical attractive force is reduced. This weaker bonding results in a weaker structure with a lower melting/boiling point.)
in case of gp 7:
As you move down the halogens group on the periodic table, the reactivity decreases because the atoms are getting larger. This causes the positive charge inside to be more shielded and the atom is less likely to gain an electron. The solubility in water also decreases moving down the group while melting and boiling points increase.

 

[funky brat]

Why does the reactivity increase down the group in Alkali Metals, and decreases down the group in the case of Halogens? :/

The alkali metals become more and more electropositive as we move down the group. This is because they have more electrons in their valence shells so they are ready to lose them.
I'm not sure though, let's wait for somebody to answer.

 

[ZohaKhan]

What is the purpose of soda lime ,sodium bicarbonate idk wot when we test whethr or not CO2 is imp for photosynthesis? anyo0nne?

 

[♫Prince Shah♫]

What is the purpose of soda lime ,sodium bicarbonate idk wot when we test whethr or not CO2 is imp for photosynthesis? anyo0nne?

i did not get uh question

 

[binder]

binder
When the reacting species, capable of losing electrons (reducing agent) and that capable of gaining electrons (oxidizing agent) are present in the same solution a direct redox reaction takes place. In direct redox reactions, the electrons move randomly in all the directions through very short distances. So, in direct redox reactions the net movement of electrons in any direction is zero. The change in chemical energy in such reactions appears as heat.
For example, Oxidation of Zn by Cu2 + .

When a strip of metallic zinc is placed in a solution of CuSO4, after sometime it is noticed that,

• A part of zinc metal plate has dissolved and has lost weight.

• The bluish colour of the solution gradually fades away.

• Reddish metallic copper has started depositing on the zinc plate or is settling down at the bottom of the beaker.

• The presence of Zn2 + ion in the solution may be confirmed by passing H2S gas through the colourless solution after making it ammoniacal by adding ammonia and ammonium chloride when white precipitate of ZnS (zinc sulphide) is formed. The solution remains electrically neutral during and after the reaction.

These observations can be explained as follows:

Solution of copper sulphate contains Cu2 + ( a q ) and SO4 2 - ( a q ) ions. When zinc plate is placed in a solution of copper sulphate, zinc being more electropositive than copper, loses electrons to form Zn2 +ions. The Cu2 + ions gain these electrons to form copper metal. This is displaced as copper metal, a reddish precipitate. As the concentration of Cu2 + ions present in the copper sulphate solution decreases the blue colour of the solution fades away. The overall reaction may be written as:

Electrons are transferred from Zn atom to Cu2 + ion directly. So, this reaction is a direct redox reaction.

Fig: - Displacement of copper from copper sulphate solution by zinc

got it

 

[♫Prince Shah♫]

got it

ty

 

[ZohaKhan]

i did not get uh question

n idk hw to xplain it..leave

 

[black widow]

What is the purpose of soda lime ,sodium bicarbonate idk wot when we test whethr or not CO2 is imp for photosynthesis? anyo0nne?

it helps to absorb CO2 thus we can identify whether CO2 is important for photosynthesis by removing it in one experiment and putting it in another

 

[ZohaKhan]

Thanks alot

 

[black widow]

Thanks alot

np

 

[Nabeel.Ahmad]

So, I'm almost done with the reading of the Chemistry book. Just left with that ''Air and Water'' topic.
Now should i read the Physics book completely, and solve Chemistry past papers along with that?
And how should i solve the papers? Should i buy the unsolved paper 2? I already have the MCQ papers from 2002-2013.. and the yearly Red-spot ATP of Chemistry.. but not the Paper 2 unsolved. I think i should buy from 2007-2013, as i don't have much time. (That will be a total of 22 Paper 2's)
Or should i buy the ATP unsolved, too? Will that be required, or i can just go through the Red-spot yearly? As ATP is almost the same pattern every time.

I think i should solve a lot of MCQ papers, to master MCQ's once and for all.

What do you suggest, black widow ?

 

[black widow]

So, I'm almost done with the reading of the Chemistry book. Just left with that ''Air and Water'' topic.
Now should i read the Physics book completely, and solve Chemistry past papers along with that?
And how should i solve the papers? Should i buy the unsolved paper 2? I already have the MCQ papers from 2002-2013.. and the yearly Red-spot ATP of Chemistry.. but not the Paper 2 unsolved. I think i should buy from 2007-2013, as i don't have much time. (That will be a total of 22 Paper 2's)
Or should i buy the ATP unsolved, too? Will that be required, or i can just go through the Red-spot yearly? As ATP is almost the same pattern every time.

I think i should solve a lot of MCQ papers, to master MCQ's once and for all.

What do you suggest, black widow ?

for Chemistry, the past papers are available on xpc and u can solve them
what i did was solve the MCQs first, then the theory and then the ATP
what u shud do is the same
first solve all the MCQ papers, as many novel concepts are there that can help ur theory
after solving all the MCQ papers solve ATP, as the questions there are simple and u will have further practice
then solve the theory