AQA Module 1 Chemistry

Hiya
I wonder if anyone can help me. How do I remember what forces and intermolecular forces are between molecules and inside molecules. For example how can I tell BaCl2 is ionic? What is the way to remember this?

Reply 1

eggnog

1

Shimon

Hiya
I wonder if anyone can help me. How do I remember what forces and intermolecular forces are between molecules and inside molecules. For example how can I tell BaCl2 is ionic? What is the way to remember this?

It depends on the differences in electronegativity values of the elements in the compound. BaCl2 is ionic because they're on opposite sides of the periodic table, hence there is a large difference in electronegativity, so much so that there is a transfer of electrons from the Ba to the two Cl s. As you move across the periodic table, say from Na to S, the elements move from forming ionic chlorides to forming ionic chlorides with covalent character, and then full on covalent chlorides.
In general, the closer together the bonding elements are in the table, the more covalent they will be.

On the subject of intermolecular forces:

ALL compounds have Van Der Waal's (temporary dipole-dipole) forces between molecules.

Compounds with polar bonds e.g. H-F, have permanent dipole-dipole forces of attraction between molecules, (although compounds such as Cl2 do not have these forces, since both atoms are of the same electronegativity, therefore the molecule is NOT polar).

Hydrogen bonds, (they're not actually 'proper' bonds, just intermolecular forces) occur between molecules of compounds such as ethanol or water. For hydrogen bonding to occur, there must be in the molecule a hydrogen atom bonded to either an N, O or F atom. This creates a very polar bond, in which the H is delta positive, and the N, O or F delta negative. Dipole-dipole forces occur between the positive H of one molecule, and the negative N, O or F of another molecule. Here's some diagrams :biggrin:

:

http://server3.uploadit.org/files/eggnog123-untitled.JPG

http://server2.uploadit.org/files/eggnog123-untitled2.JPG

I don't know whether you wanted a full explanation or not, but it was good revision for me for the synoptic paper so...bleh.

Reply 2

stratomaster

Ionic - attraction between metal and non-metal atoms.
Definition: Electrostatic attraction between oppositely charged ions.

Covalent - attraction between non-metal atoms.
Definition: a shared pair of electrons.

Is that what you're after?

Reply 3

Shimon

OP

stratomaster

Ionic - attraction between metal and non-metal atoms.
Definition: Electrostatic attraction between oppositely charged ions.

Covalent - attraction between non-metal atoms.
Definition: a shared pair of electrons.

Is that what you're after?

Thanks alot!!

AQA Module 1 Chemistry

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