Biology; Chemistry; Physics: Post your doubts here!

funky brat

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Nabeel.Ahmad said:
So the oxidation state of pure ''elements'', uncombined with any other element to form compounds, is zero.
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The oxidation state of an element is always 0 e.g H2, Cl2, O2 etc.
The sum of any compound has an oxidation state of zero e.g H2SO4.
Hydrogen, oxygen, 1st group and 7th group elements have fixed oxidation states like +2, -2, 0 and 1 etc.
 
♫Prince Shah♫

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Nabeel.Ahmad said:
In Alkali Metals, why does the melting point decrease as we go down the group?
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May this help uh...
Important 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.)
(y)
 
black widow

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Nabeel.Ahmad said:
In Alkali Metals, why does the melting point decrease as we go down the group?
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as we go down the group, the size of the atom increases
the nuclei holds the outer electron. for metals to become stable, they need to lose electron(s). thus as the size of the atom increases, the force of attraction between the nuclei and electron decreases and it is more easily separated which is y the melting point decreases down the group
 
black widow

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♫Prince Shah♫ said:
May this help uh...
Important 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.)
(y)
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but for the group VII elements, the melting points increases down the group
 
black widow

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can someone plz answer my question
y is it that i find very few people who actually solve bio questions
 
Nabeel.Ahmad

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black widow said:
but for the group VII elements, the melting points increases down the group
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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.
 
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