Counting Oxygen Atoms

Similarly, the (M + 2) peak contains intensity contributions from oxygen, Cl, Br, and multiple heavy isotopes of carbon, hydrogen, and so on. A general formula for compounds that contain only C, H, N, O, F, P, and I can be used to ascertain the number of oxygen atoms, in theory. Examination of Table 10.4 shows that oxygen has two important isotopes, and 0, separated by 2 Da, with a relative abundance 0/ 0 of 0.2%. The number of oxygen atoms in a molecular ion can be calculated from 

This equation again ignores the contribution from hydrogen. Compounds containing the halogens Cl and Br will be discussed later in this chapter. Iodine does not affect the equation, since iodine is monoisotopic. 

While Equation 10.3 can be used, in theory, to calculate the number of oxygen atoms in a compound, in reality, the 0 isotope is of low abundance, and oxygen-containing compounds often fragment so that the molecular ion is of low intensity or not detected. In practice, the observation of isotope information for oxygen is often difficult. 

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The green oxygen m Figure 1 5 owns three unshared pairs (six electrons) and shares two electrons with nitrogen to give it an electron count of seven This is one more than the number of electrons m the valence shell of an oxygen atom and so its formal charge is —1... 

Now that we know how to count carbon atoms, we must learn how to count the hydrogen atoms in a bond-line drawing of a molecule. Most hydrogen atoms are not shown, so bond-line drawings can be drawn very quickly. Hydrogen atoms connected to atoms other carbon (such as nitrogen or oxygen) must be drawn ... 

In addition to the electron on the oxygen from the C-0 bond, the oxygen also has three lone pairs. A lone pair is when you have two electrons that are not being used to form a bond. Lone pairs are drawn as two dots on an atom, and the oxygen above has three of these lone pairs. You must remember to count each lone pair as two electrons. So we see that the oxygen atom actually has seven electrons, which is one more electron than it is supposed to have. Therefore, it will have a negative charge ... 

Let s try to determine the hybridization state of the carbon atom in the center. We begin by counting the number of atoms connected to this carbon atom. There are 3 atoms (O, H, and H). The oxygen atom only counts as one. 

Of the remaining two possibilities, we must choose a parent that includes both carbon atoms of the double bond. Only one parent chain contains both the functional group and the two carbon atoms of the double bond. Containing the functional group means that the OH is connected to a carbon that is part of the chain. We do not count the oxygen atom itself as part of the chain. It is only attached to the chain. So the chain above is made up of four carbon atoms. 

The oxygen atom wins. Next comes the one with three carbon atoms. The remaining two are the same, so we need to move out one farther on the chain and compare again. Remember to count the double bond like two carbon atoms ... 

Ans. We want to measure the mass of a large number of carbon atoms, and divide the total mass by the number of atoms. However, we have the additional problem here, compared with counting sheets of paper, that atoms are too small to count. We can "count" them by combining them with a known number of atoms of another element. For example, to count a number of carbon atoms, combine them with a known number of oxygen atoms to form CO. in which the ratio of atoms of carbon to oxygen is 1 1. 

The electrons shared between the oxygen atoms arc counted one for each atom. Peroxide oxygen is assigned an oxidation state of - 1 by rule 6 also. 

Borates can be viewed as complex salts in which the Lewis basicity of the structural unit must match the Lewis acidity of the interstitial complex to produce a stable structure. The relationship between basicity of the borate structural unit and its BO4/BO3 ratio was mentioned above, indicating that each specific structural unit has an associated basicity. It was recently shown that the Lewis basicity of borate structural units correlates with the average coordination number of the oxygen atoms they contain, counting H-bonds... 

In formaldehyde (CH2O), for example, carbon bonds with two hydrogen atoms and double-bonds with one oxygen atom. So carbon effectively has three bonds present. Remember, the double bond counts as only one bond for the purposes of moleculcir geometry. 

Such simple considerations give the chemist very ready information about structure. As another example, a compound containing a single oxygen atom might quickly be determined to be an ether or a carbonyl compound simply by counting unsaturated sites. ... 

Now it is balanced in number of atoms by counting the hydrogen ions (8 on the Icli-hand side), and the oxygen atoms tan excess of 4 on the left-hand side). Therefore 4 ILO is added to the right-hand side ... 

Count the atoms of each element to find the formula. Then look at each atom in the structure to find what is needed for completion. Each carbon (gray) should have four bonds, each oxygen (red) should have two bonds and two lone pairs, and each nitrogen (blue) should have three bonds and one lone pair. 

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