7 replies to this topic

[gary]

Hey,

Can someone help me with these questions please:

An element has the electron arrangement 2,8,18,18,8,2

What will the main type of bonding be between its atoms?

Why does this electron have a higher boiling point thatn its neighbour with an electron arrangement 2,8,18,18,8,1?

CH4 and CF4 are both polar molecular compounds in which the moclecules both have the same tetrahedral shape.

Which would you expect to have the higher boiling point and why?

The HCF3 molecule also has a tetrahedral shape and its boiling point is higher than that of CH4 and CF4. Suggest a reason for this.

Silicon dioxide and carbon dioxide have similar names and similar formulae. Yet these two compounds are very different in their properties.
Explain in terms of bonding and structure why silicon is a high melting point solid and carbon dioxide is a gas at room temperature.

SiO2 CO2

[Infinite_Dreams]

1) Metallic bonding between it's atoms due to the two extra negatively charged electrons which will be delocalised, and attracted to the positively charged nuclei of neighbouring atoms.

2) More outer electrons means a stronger attraction to the positively charged nuclei of neighbouring atoms, and thus more energy is needed to break these attractions to cause it to melt.

3) CF4 due to it having a larger molecules, meaning that it will have larger Van Der Waals attractions between the molecules. ***

4) It contains hydrogen bonding (H---F).

5) Silicon dioxide is a covalent network substance. In networks, the atoms are joined by strong covalent bonds between elements in all directions, forming a large network of in this case, silicon and oxygen joined together. These bonds require very large amounts of energy to break, and room temperature alone is not enough to even reduce it to a liquid, thus it is a solid at room temperature.

Carbon dioxide on the other hand is held together by intramolecular covalent bonds, and weak intermolecular Van Der Waals forces. The Van Der Waals forces require little energy to break, and as a result room temperature is enough to cause these molecules to come apart and exist as only a gas.

***Not 100% sure on this...I'd look at the answers other people offer before putting this down.

[George]

CF4 due to it having a larger molecules, meaning that it will have larger Van Der Waals attractions between the molecules.

I agree with that (and the others!)

[gary]

Thank You

[Discogirl17]

If you have anymore questions then please do not hesitate to PM me

[Froggy]

4) It contains hydrogen bonding (H---F).

In that molecule does the Hydrogen actually connect to a Flourine molecule, I mean, shouldn't all the fluorine atoms and the hydrogen be connected to the Carbon atom, therefore it only having Polar-Polar attractions, not Hydrogen bonding? I hope that made sense...

[Infinite_Dreams]

HCF3 is polar. The negative charge is on the flourine, and the positive charge on the hydrogen. Hydrogen bonding occurs between the strongly electronegative atoms Nitrogen, Oxygen and Fluorine.

Since fluorine carries a negative charge, and the hydrogen a positive charge, a very strong polar-polar attraction occurs between them. That polar-polar attraction is called the Hydrogen Bond, and occurs in the case of fluorine.

[George]

In that molecule does the Hydrogen actually connect to a Flourine molecule, I mean, shouldn't all the fluorine atoms and the hydrogen be connected to the Carbon atom, therefore it only having Polar-Polar attractions, not Hydrogen bonding? I hope that made sense...

HCF3 is polar.

I think that's right. I don't think there is hydrogen bonding in HCF₃ - that requires a hydrogen atom to be directly bonded to a nitrogen, oxygen or fluorine atom. But, the molecule overall is polar, since the fluorine and hydrogen have different electronegativities.