6246Lect02_S10

6246Lect02_S10 - Advanced Environmental Geochemistry, GLY...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Advanced Environmental Geochemistry, GLY 6246, ©David Warburton, 2010 1 Figure 2-1 LECTURE 2 - STRUCTURE AND BONDING IN WATER Lect02, slide 2 here Water, known chemically as dihydrogen oxide, consists of two hydrogen atoms and one oxygen atom. The formula is written H 2 O and may be represented diagrammatically in several ways, a few of which we will examine. Each hydrogen atom is bonded to the oxygen. Since each hydrogen atom has one valance electron and the oxygen atom has six valance electrons (see Figure 2-1), the traditional picture of bonding in water is that of two strong covalent bonds between the individual hydrogens and the oxygen. In covalent bonding an electron from each atom is shared with the other atom. This would give the hydrogens each two electrons, and give the oxygen eight electrons. These numbers complete the 1s shells for the hydrogen and the 2s shell for the oxygen. This should lead to a very stable molecule. Figure 2-2 represents such a molecule. Lect02, slide 3 here Lect02, slide 4 here
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Advanced Environmental Geochemistry, GLY 6246, ©David Warburton, 2010 2 Figure 2-2 Covalent bonding therefore represents an equal sharing of electrons between two atoms. If the two atoms are identical, for example oxygen in O 2 or hydrogen in H 2 we should expect that the sharing is equal. However, if the atoms are not identical, we might expect that one atom will attract electrons more strongly than the other and that the sharing will be unequal. In the extreme case we could get a compound like sodium chloride, usually written Na + Cl - . This indicates that the chlorine atom attracts the electron much more strongly than the sodium atom. In effect sodium donates an electron to chlorine. This type of bonding is of course known as ionic bonding , which may be defined as bonding between ions created when one atom donates one or more electrons to another atom . It is known that atoms that are far apart on the periodic table have predominantly ionic bonding while atoms that are close together have dominantly covalent bonding. This leads us to ask, "Is the traditional picture of pure covalent bonding in water correct?” Linus Pauling used the concept of electronegavity to help answer this question. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It is the difference in the electronegativities of the atoms that is significant. Lect02, slide 5 here The most commonly used scale of electronegativity was created by Pauling. Lect02, slide 6 here Pauling (1960, p.90) lists the electronegativity of hydrogen as 2.1 and of oxygen as 3.5. Here, the difference is 1.4.
Background image of page 2
Advanced Environmental Geochemistry, GLY 6246, ©David Warburton, 2010 3 Figure 2-3 Lect02, slide 7 here Pauling (1960, p. 99) represents graphically the amount of ionic character versus the difference in electronegativity (Figure 2-4). From his graph, a difference in electronegativity of 1.4 corresponds to about a 39% ionic character in the bond. More exact work indicates that the true percent ionic character is
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 10

6246Lect02_S10 - Advanced Environmental Geochemistry, GLY...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online