Question

look at this compound, why does magnesium has dative and covalent bonds with nitrogen?

Answer 1

The solid lines between N and Mg are actually ionic bonds. N has 5 valence electrons (2 of which are paired). Of the 3 that are unpaired, 2 are part of covalent bonds with adjacent carbon atoms. N accepts an extra electron to complete its octet, but gets a formal charge of -1. This allows for formation of an ionic bond with Mg, which is +2. Two of these charged N atoms therefore neutralize the charge of the central Mg.

As for the coordinate (dative) covalent bonds, Mg has empty orbitals - the ionic bonds with the charged N atoms give it only 4/8 possible valence electrons. The other two N atoms (dotted lines) have a formal charge of 0 since they form three covalent bonds with adjacent carbon atoms, but they still have a lone pair. Therefore, just to improve stability, each of these N atoms can "donate" its lone pair to Mg in order to complete its octet.

Answer 2

Ionic bonds
Ionic (or electrovalent) Bonding is formed by the transfer of electrons. For example the sodium atom has one electron on its outer shell, the chlorine atom has seven electrons on its outer shell. During ionic bonding the sodium ion transfers its outer electron to the chlorine atom, and becomes a Na+ ion with the stable configuration of an inert gas. At this time the chlorine atom gains the transferred electron and so forms a Cl- ion also with an inert gas configuration. This results in electrostatic attraction between the new ions of the compound, and so ionic bonds are formed.

MgO, CaF2 and Li2O are other examples of compounds that use ionic bonding.
Task 1.3a.1 Draw dot and cross diagrams for these examples. LiF, KF, LiCl, NaF, MgCl2, AlF3, MgO, MgS, Na2O, CaF2 and Li2O, Al2O3.
Ionic size (radii) depends on: Principal quantum number of outer shell. Higher number, bigger ion. K+ bigger than Na+.
Nuclear charge. Higher charge, smaller ion. Mg (+12 charge) smaller than Na (+11 charge)
Strength of ionic bonds: Ionic radii - small ions, strong bonds. Ionic charge - high charge, strong bonds.
Direction: Ionic bonds are non-directional and have equal influence in all directions
Covalent bonds.
Covalent bonding involves atoms of non-metals completing their outer shells by sharing pairs of electrons. E.g. the hydrogen atom has one electron in its outer shell. Within the hydrogen molecule, (H2) each atom contributes one electron to the bond. Consequently each hydrogen atom now has control of 2 electrons, one of its own and a second from the other atom, giving it the configuration of an inert gas (He).

Task 1.3a.2 Draw dot and cross diagrams to show the bonding in HF, F2, NH3, CH4, H2O, F2O, CHCl3, O2,CO2, C2H4, C2H2.
Dative covalent bonds.

Dative covalent bonding. Normally each atom contributes 1 electron to a covalent bond. In a dative covalent bond, 1 atom contributes both electrons to the covalent bond. For a dative covalent bond, an arrow replaces the straight line.
This hydrated magnesium ion has 6 coordinate (dative covalent) bonds formed by the lone pairs on each of the 6 surrounding water molecules.
H
|
H--N->H
|
H

Answer 3

guys, can i say that mg has two electrons to donate, therefore two bonds with the two Nitrogen atoms and since Nitrogen has electons to donate, thus two dative bonds with Mg? but this means two are ionic and two are dative.. my answer to that mcq question is that Mg forms two dative bonds and two covalent bonds.. O.O?

Answer 4

is sigma bond a covalent bond?

Answer 5

Hmm not sure about the answer then since I thought it was two ionic and two coordinate covalent. A sigma bond is a covalent bond, but so is a pi bond. Not sure how much you know about the shapes of orbitals, but the reason why a sigma is so much stronger than a pi is because the orbitals of adjacent atoms overlap face-to-face instead of laterally.

Answer 6

the ans is two covalent and two dative, which is weird, i thought there's ionic too! yes i do know a bit about their shapes!