Chemistry - covalent and metallic bonding
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identify 4 covalent compounds from the following list.
MgSO4, NH3, CHCl3, Br2, CaCl2, SO2
the highlighted ones are the substances which i think are covalent compounds. May i know what's the 3rd one? covalent compounds are supposed to be non-metals, isn't it? but then again, it can't be Br2/ please help and justify your answer with explanation. thank you!
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Br2 is the other covalent compound.
halogens exist as simple diatomic molecules where the 2 atoms are linked by a covalent bond.
hopefully this answers your qn.
for MgS04 and Cacl2 they are both ionic compounds. Ca and Mg are group 2 metals.
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"Co" = Sharing. "Valent" = Valence electrons.
Typically, the purpose of covalent bonds are to achieve a stable octet (or duplet, for hydrogen).
Reason for the idea (but don't make it a dogma, understand it intelligently) for "non-metal & non-metal = covalent bonding" is due to the (relatively) smaller difference in electronegativites between the species involved.
"Metal & non-metal = ionic bonding" is due to the presence of cations (usually the metal) and anions (usually the non-metal). Take note, that there are non-metal cations too (see Postscript below).
Metals are electropositive (ie. strong tendency to lose electrons, hence forming cations) while for non-metals, electronegativity (ie. tendency to gain electrons, h increases from left to right, and from bottom to top, of periodic table, with the most electronegative element being F.
The intramolecular Br-Br bond is obviously purely covalent because bromine has the same electronegativity as bromine. The intermolecular forces between Br2 molecules, are induced dipole - induced dipole van der Waals forces.
Mg2+ cation, SO4 2- anion. Electrostatic forces of attraction = ionic bonding.
Ca2+ cation, Cl- anion. Electrostatic forces of attraction = ionic bonding.
NH3 - trigonal pyramidal with net dipole moment as N is more electronegative than H. Hence hydrogen bonding and/or permanent dipole - dipole interaction exists between NH3 molecules. But intramolecular bonds between N and H are (polar) covalent.
CHCl3 - trichloromethane. Polar covalent bonds intramolecular present in this tetrahedral molecule, particularly between the highly electronegative chlorine and the less electronegative carbon. (carbon is only slightly more electronegative than hydrogen). Net dipole moment exists in CHCl3, a polar molecule. Hence permanent dipole - dipole interaction (but not hydrogen bonding) exists between CHCl3 molecules.
SO2 - sulphur dioxide. Polar covalent bonds intramolecular bonds present in this bent / non-linear / v-shape molecule. Oxygen is more electronegative than sulphur. Molecular is polar overall, with permanent dipole - dipole intermolecular interactions.
PS.
Regarding the simplified (and false) 'dogma' that "non-metal & non-metal = covalent, metal & non-metal = ionic", you may observe the limitations of said 'dogma' in considering the following.
1) There can be non-metal cations too, eg. NH4+ (when the Bronsted Lowry base NH3 abstracts a proton to become the conjugate acid NH4+, ie. a lone pair on NH3 becomes a bond pair between N and the incoming H, causing a positive formal charge to result on the central N species). Hence, there exist electrostatic forces of attraction, ie. ionic bonding, between non-metal oppositely charged ions, eg. ammonium cation and sulphate anion. Take note that hydrogen, can form both cations and anions, known as protons (think : when a typical hydrogen atom (not deuterium or tritium isotope) loses an electron, what is left? any neutrons?) and hydride ions, respectively.
2) Dative (ie. 'donated') or coordinate covalent bonds, are also present between metals (usually transition metals) and non-metal electron donors known as ligands, to form complex ions. The ligands behave as nucleophiles towards the electrophilic central metal species. Eg. Four monodentate NH3 ligands donate their lone pairs to form dative/coordinate covalent bonds with a central Cu2+ ion, forming the tetraaminecopper(II) ion, [(NH3)4 Cu]2+ complex ion.
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TS only ask a O level question... Why you'all give him so much explanation? =.=" But it's a good thing to learn more.~
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Originally posted by bonkysleuth:
identify 4 covalent compounds from the following list.
MgSO4, NH3, CHCl3, Br2, CaCl2, SO2
the highlighted ones are the substances which i think are covalent compounds. May i know what's the 3rd one? covalent compounds are supposed to be non-metals, isn't it? but then again, it can't be Br2/ please help and justify your answer with explanation. thank you!
i am not going to repeat what the others have explained so well.
well, from your logic, isn't Br2 non-metal? and if so, isn't it covalent?