Bonding 2
Covalent Bonds - hydrogen has 1 electron in its orbit. It wishes to gain another one so its 1s can be filled. If two hydrogen atoms meet and the first hydrogen atom gave its one electron away to the second hydrogen atom. The second one would be complete (H-) but the first atom would be unstable with 0 electrons. As a result, they can share electrons known as covalent bonding. It is now H2, a diatomic (two atom) compound.
Other diatomic forms include - oxygen, nitrogen, fluorine, chlorine, bromine, iodine.
Differences between the two;
Ionic - Metal and Non-metal Covalent - Two non-metals
Ionic - Usually solid at room temperature Covalent - Can be solid, liquid or gas
Ionic - Melting point is higher than colvalent Covalent - Melting point is lower
Ionic - Tend to be electrolytes Covalent - Tend to be non-electrolytes.
Multiple Bonds - In diatomic molecules, only one electron is shared. However in other covalent bonds - the atoms share more than one electron pair.
Nitrogen (N2) is in the VA family meaning it has 5 outer valence electrons and needs three more to complete its octet (8 electrons). A nitrogen atom can fill its octet by sharing three electrons with another nitrogen atom - forming 3 covalent bonds. e.g N (with 5 in its outer shell) plus N (with 5 in its outer shell) = :N:::N:
Co2 is another example of this. Carbon has four valence electrons and oxygen has 6. Carbon can give away two of its valence electrons to each oxygen atoms to form Co2 (a double bond).
Structual Formulas - the molecular formula used in ionic compounds is enough to identify the compounds but not enough to identify covalent compounds. For instance C2H6O could be more than one compound. The only way to identify it is to look at how the atoms are bonded.
Compounds with the same molecular formula but different structures are called isomers to each other.
Basic Bonds - 1)Find the central Atom.The central atom is usually the one which forms more than one covalent bond when trying to fill their valence energy level. e.g oxygen, nitrogen, phosphorus, sulfur, silicon, carbon.
In the case of H2O, oxygen is the central atom and the two hydrogen atoms are bonded to it.
2)Count the valence electrons. each hydrogen has 1 electron and oxygen has 6 valence electrons = 8 electrons. a)Work out how many valence electrons are needed. (usually 8, unless its hydrogen its 2)The number of valence electrons available. e.g boron trifluoride (BF3). Boron - 5 (3 valence electrons), Flouorine - 9 (7 valence electrons). 9x3 as there are 3 fluorine particles = 21. 21+ 3 = 24 valence electrons total.
so for H2O; a)8 valenece plus 2 for each of the hydrogen atoms = 12 b) 6 valence for oxygen plus 1 for each of the hydrogens = 8.
c)12-8 = 4. 4 bonds shared in water. 4/2 = 2 which means there are two bonds.
Distribute four electrons to account for the bonds. Then use the remaining electrons to distribute around the other atoms.
Electronegativites -Atoms may share electrons through bonds but that doesn’t mean they share equally. Electronegativity is the strength an atom has to attact a bonding pair of electrons to itself. Electronegativities increase from left to right in a period and decrease top to bottom in a family.
A bond where an electron share is equally paired is known as a nonpolar covalent bond. A bond where the electron pair is shifted toward one atom is known as polar covalent bond.
The atom which attracts the bonding electron pair is slightly more negative.e.g in hydrogen chloride (Hcl) - hydrogen had an electonegativity of 2.1 and chlorine has an electronegativity of 3.0. Because chlorine has a larger value, the electron pair bondng Hcl shifts toward the chlorine atoms. If the atoms have very different electronegativities - they are likely to form ionic bonds instead of covalent.
Guide to types of bonds - Electronegativity differences - If its between 0.0-0.2 = nonpolar covalent. Between 0.3 and 1.4 = polar covalent. Anything over 1.5 is likely to be ionic.
Polar covalent molecules can act as weak electrolytes because the bond allows the substance to act as a conductor.
Polar molecules are dipoles (one end having a partial negative charge and the other end having a partial positive charge). Attraction and force between molecules is known as intermolecular force. There are three different types of force;
London force - a weak force occuring between non covalent molecules.
Dipole-Dipole interaction - when the positive end of one dipole is attracted to the negative end of another dipole.
Hydrogen bond - An extremely strong dipole-dipole interaction when hydrogen is bonded to one of the three extremely electromagnetic elements -O, N or F.
