Bonding

Question 1

What allows for electrons to be promoted within quantum shells e.g sulfur can promote electrons from the 3s and 3p subshell to the 3d subshell

Answer 1

• all of these sub shells are in the same quantum energy level (n=3)

-therefore the difference in energy between the sushells isn’t HUGE, so not too much energy needs to be put in to promote the electrons

(As you move lower down in the periodic table octet expansion becomes rarer as gaps within subshells get larger as you move down quantum shells)

Question 2

What is a the pro to expanding an octet for an atom, despite it taking Energy to promote the electrons

Answer 2

• they can form more covalent bonds
  -covalent bond formation is exothermic, therefore the more bonds you form, the form energy you release
  -so the atom is more stable

Question 3

Explain the bonding in the Nitrate (NO3^-1 ion)

Answer 3

-Nitrogen forms four bonds with 3 oxygen atoms
-3 of the bonds are normal covalent bonds
-the last bond is a dative covalent bond from nitrogen to oxygen, as nitrogen has already used 3 of its valence electrons in covalent bond but has a lone pair left

-2 of the oxygens have to gain an external electron as they only have 1 bond to nitrogen (1 has 1 covalent and 1 has 1 dative covalent bond)
-However the dative covalent bond gives nitrogen a partial positive charge
-so the overall change of the polyamtoic ion is -2 + 1 = -1

Question 4

Why can’t nitrogen expand its octet?

Answer 4

-It’s electron configurations is 1s2 2s2 2p3 , it does not have a d subshell and therefore no vacant d orbitals to promote electrons to

• Promoting an electron from the 2p to the 3s sub shell would take way too much energy anyway (you’re going up a whole shell) , and is not worth the pay off, as the atom can be stable without expanding its octet

Question 5

What makes a (covalent) bond polar?

Answer 5

-When one of the elements in the bond is more electronegative than the other

-The more electronegative atom attracts the electron pair more strongly,giving it a partial negative charge, and the less electronegative atom (now further away from the bonding pair) gets a partial positive charge

Question 6

What is the quantitative scale to measure electronegativity of an atom?

Answer 6

-Pauling scale

-goes from 0.7 (least electronnegative atom - francium) to 4.0 (most
electronegative atom - fluorine )

-electronegative increases right and up across the periodic table

Question 7

Give the difference in electronegative values on the Pauling scale for : non-polar covalent bond, covalent bond, ionic bond

Answer 7

Non-polar covalent : 0.0-0.4 (usually molecules with two of the same atom e.g Br2 , N2 , O2)

Polar covalent : 0.4-1.7

Ionic bond : difference in electronegativity < 1.7

Question 8

How come you can get a covalent bond between a non-metal and a metal? Give an example

Answer 8

• If the difference in electronegativity between the metal and non-metal atom is less than 1.7, the bond is technically polar covalent

-example : AlCl3 , the Al-Cl bond is technically polar covalent, as the difference in electronegativity between Al and Cl is 1.5 ( >1.7)

Question 9

If Br2 is non polar, how come during electrophilic addition we draw dipoles on the bromine atoms?

Answer 9

-The C=C bond of the alkene has such a high electron density it actually induces a dipole in Br2

-The Br atom closest to the C=C bond gets a partial positive charge as all of the electrons are repelled to the bromine atom furthest away from the C=C bond