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Chemistry Doubt :S <urgent>

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THEIGBOY:
hello every1,
How are you guys,
If there is any chemistry genius out there... please explain this part from the syllabus :D
(pg 10 of syllabus)
(a) *describe ionic (electrovalent) bonding, as in sodium chloride and magnesium oxide,
including the use of ‘dot-and-cross’ diagrams
(b) *describe, including the use of ‘dot-and-cross’ diagrams,
(i) covalent bonding, as in hydrogen; oxygen; chlorine; hydrogen chloride; carbon
dioxide; methane; ethene
(ii) co-ordinate (dative covalent) bonding, as in the formation of the ammonium ion and in
the Al 2Cl 6 molecule
(c) *explain the shapes of, and bond angles in, molecules by using the qualitative model of
electron-pair repulsion (including lone pairs), using as simple examples: BF3 (trigonal);
CO2 (linear); CH4 (tetrahedral); NH3 (pyramidal); H2O (non-linear); SF6 (octahedral)
(d) *describe covalent bonding in terms of orbital overlap, giving ? and ? bonds
(e) *explain the shape of, and bond angles in, the ethane, ethene and benzene molecules in
terms of ? and ? bonds (see also Section 10.1)

Also can you please explain Ideal gas behaviour and it's assumptions, and also deriving Mr from PV=nRT


Thanks sooooo much in advance,
THEIGBOY
(f) predict the shapes of, and bond angles in, molecules analogous to those specified in (c) and (e)

Saladin:
(a) Basically, you need to know the definition of an ionic bond. And show ionic bonds via a dot-and-cross diagram.

(b) Define what co-valent bonding is and be able to show it in a dot-and-cross diagram.

Know how to draw a dative co-valent bond in the Al2Cl6 molecule. Has to be shown with an arrow.

(c) Know bond angles of the molecules stated, i would know more if there were more in the book. Also electron repulsion theory, basically why they are at these angles.

Srry dnt hav much more time, will reply again if possible or if ur q is not answered yet.

Sue T:
this attachment is 4:

c) *explain the shapes of, and bond angles in, molecules by using the qualitative model of
electron-pair repulsion (including lone pairs), using as simple examples: BF3 (trigonal);
CO2 (linear); CH4 (tetrahedral); NH3 (pyramidal); H2O (non-linear); SF6 (octahedral)


(f) predict the shapes of, and bond angles in, molecules analogous to those specified in (c) and (e)

tmisterr:
For  ideal gas behaviour, first you need to understand the kinetic theory of gases which is gotten from the main idea that gases consist of molecules in a constant state of random motion:
Basically it states that:
1. Gases occupy the space of the container they are placed in
2. Gases exert pressure on the container by colliding on the walls of the container
3. Gas molecules continue moving in a straight line until they collide with the walls of the container of with other gas molecule and these collisions are perfectly elastic (that is all the kinetic energy is the same before and after collision)

An ideal gas is then a gas which has the following properties:
1. It has no intermolecular forces of attraction
2. It has mass but negligible size (that is it does not occupy space)
3. It collisions are perfectly elastic

the ideal gas equation is PV=nRT. P is pressure in Pascals, V is volume in metre cubed, n is number of moles, R is the ideal gas constant (i think about 8.314) and T is temperature in Kelvin. To use this equation, you must make sure your values are converted to these units. This equation works best for ideal gases.

Real gases have two major problems that can affect values while using this equation:
They occupy space and they have intermolecular forces of attraction. However, real gases can approach real behaviour by using gases that are very small in size like Hydrogen or Helium, at high temperature and low pressure (high volume) with these conditions, intermolecular forces are greatly reduces.

So to use the above equation, it would be best to carry out the experiment to calculate Mr at low pressure and high temperature. The experiment to calculate Mr. is a bit hard to explain without a diagram so try look in your reference book, but you usually use a volatile liquid of a known mass in a small syring, which is injected to another gas syringe in an oven of a known temperature. The volatile liquid will vaporize in the gas syringe and the volume of the gas read from the syringe. The experiment is done at atmospheric pressure (1atm or 101KPa) so since you know P,V, R and T, then you use the ideal gas equation to calculate n. once you know the mass and number of moles, then calculating Mr is very easy.

THEIGBOY:
Thanks soooo much for your urgent replies... :D

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