Nitrogen atom valence electrons

Although the nonmetals do not readily form cations, many of them combine with oxygen to form polyatomic oxoanions. These anions have various stoichiometries, but there are some common patterns. Two second-row elements form oxoanions with three oxygen atoms carbon (four valence electrons) forms carbonate, C03, and nitrogen (five valence electrons) forms nitrate, NO3. In the third row, the most stable oxoanions contain four oxygen atoms Si04 -, P04 -, S04, and CI04. ... 

The assumption of resemblance reveals a second, subtler, presupposition. The periodic chart places elements in columns, or groups, based on the numbers of their valence electrons. Thus, nitrogen is placed in group 5 (15 in the IUPAC scheme) even though it frequently expresses a valence of three. Fixed-period molecules with the same total number of atomic valence-shell electrons ( isoelectronic, horizontally isoelectronic, or isosteric molecules such as N2 and CO) usually have properties more similar than do molecules selected at random. Molecules whose atoms come from different periods but have the same numbers of valence electrons ( vertically isoelectronic or isovalenf molecules such as the salts LiF, Nal, and CsCl), often have somewhat similar properties. So, the sum of the atomic valence electron counts, i.e., the sum of the atomic group numbers, is important. Thus, it appears that using... 

Moving now to nitrogen we see that it has four covalent bonds (two single bonds + one double bond) and so its electron count is 5(8) = 4 A neutral nitrogen has five electrons m its valence shell The electron count for nitrogen m nitric acid is one less than that of a neutral nitrogen atom so its formal charge is +1... 

The number of valence electrons in an atom of a main-group element such as nitrogen is equal to its group number. In the case of nitrogen this is five. 

Octet rule (Section 1.3) When forming compounds, atoms gain, lose, or share electrons so that the number of their valence electrons is the same as that of the nearest noble gas. For the elements carbon, nitrogen, oxygen, and the halogens, this number is 8. 

The number of covalent bonds an atom forms depends on how many additional valence electrons it needs to reach a noble-gas configuration. Hydrogen has one valence electron (Is) and needs one more to reach the helium configuration (Is2), so it forms one bond. Carbon has four valence electrons (2s2 2p2) and needs four more to reach the neon configuration (2s2 2p6), so it forms four bonds. Nitrogen has five valence electrons (2s2 2p3), needs three more, and forms three bonds oxygen has six valence electrons (2s2 2p4), needs two more, and forms two bonds and the halogens have seven valence electrons, need one more, and form one bond. 

The same is true for the nitrogen atom in ammonia, which has three covalent N-H bonds and two nonbonding electrons (a lone pair). Atomic nitrogen has five valence electrons, and the ammonia nitrogen also has five—one in each of three shared N-H bonds plus two in the lone pair. Thus, the nitrogen atom in ammonia has no formal charge. 

Notice that in each case the oxygen or nitrogen atom is surrounded by eight valence electrons. In each species, a single electron pair is shared between two bonded atoms. These bonds are called single bonds. There is one single bond in the OH- ion, two in the H20 molecule, three in NH3, and four in NH4+. There are three unshared pairs in the hydroxide ion, two in the water molecule, one in the ammonia molecule, and none in the ammonium ion. 

For the same reason we discussed for oxygen atoms, the nitrogen atom is most stable when it has the maximum number of partially filled valence orbitals. This keeps the electrons as far apart as possible. The most stable state of the nitrogen atom is as follows ... 

The Lewis symbol for nitrogen, for example, represents the valence electron configuration 2s22pA.12p>112p 1 (see 1), with two electrons paired in a 2s-orbital and three unpaired electrons in different 2p-orbitals. The Lewis symbol is a visual summary of the valence-shell electron configuration of an atom and allows us to see what happens to the electrons when an ion forms. 

For example, nitrogen ( N ) has five valence electrons and needs three more electrons to complete its octet. Chlorine (-CL) has seven valence electrons and needs one more electron to complete its octet. Argon OArO already has a complete octet and has no tendency to share any more electrons. Hydrogen (H-) needs one more electron to reach its helium-like duplet. Because hydrogen completes its duplet by sharing one pair of electrons, we say that it has a valence of 1 in all its compounds. In general, the valence of an element is the number of bonds that its atoms can form. 

The molecule has one nitrogen atom p ). Interpreting the parentheses in the formula reveals that there are four carbon atoms p ) and eleven hydrogen atoms (5 ). You should be able to verify that the valence electron count is 32 e. ... 

Nitrogen is more electronegative than carbon. Place the last two valence electrons on this atom, completing its octet and giving the provisional Lewis structure. 

There are 14 valence electrons, and the atoms are bonded in the order listed. In the final Lewis structure, oxygen has two lone pairs and nitrogen has one. 

Imine and ethylene have the same number of valence electrons and similar bonding frameworks. Compare these bonding pictures with those for ethylene. Notice that they are identical, except that a lone pair on the nitrogen atom replaces one of the C—H bonds. 

A ligand must have a lone pair of electrons that it donates to form a bond to the metal. For example, the Ni— bonds in [Ni (NH3)g form by overlap of an empty valence orbital on the metal with the lone pair. s orbital on the nitrogen atom. The water ligands in [Ni (H2 0) ] " coordinate to the metal in a similar manner, with the oxygen atoms donating lone pairs to form Ni—O bonds. 

Ammonia is a prime example of a Lewis base. In addition to its three N—H bonds, this molecule has a lone pair of electrons on its nitrogen atom, as Figure 21-1 shows. Although all of the valence orbitals of the nitrogen atom in NH3 are occupied, the nonbonding pair can form a fourth covalent bond with a bonding partner that has a vacant valence orbital available. 

Trimethylboron is an example of one type of Lewis acid. This molecule has trigonal planar geometry in which the boron atom is s hybridized with a vacant 2 p orbital perpendicular to the plane of the molecule (Figure 21-11. Recall from Chapter 9 that atoms tend to use all their valence s and p orbitals to form covalent bonds. Second-row elements such as boron and nitrogen are most stable when surrounded by eight valence electrons divided among covalent bonds and lone pairs. The boron atom in B (CH ) can use its vacant 2 p orbital to form a fourth covalent bond to a new partner, provided that the new partner supplies both electrons. Trimethyl boron is a Lewis acid because it forms an additional bond by accepting a pair of electrons from some other chemical species. 

The simplest type of Lewis acid-base reaction is the combination of a Lewis acid and a Lewis base to form a compound called an adduct. The reaction of ammonia and trimethyl boron is an example. A new bond forms between boron and nitrogen, with both electrons supplied by the lone pair of ammonia (see Figure 21-21. Forming an adduct with ammonia allows boron to use all of its valence orbitals to form covalent bonds. As this occurs, the geometry about the boron atom changes from trigonal planar to tetrahedral, and the hybrid description of the boron valence orbitals changes from s p lo s p ... 

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