Unit 1 - MoleculesElaboration - The Octet Rule

In section 3.2 the concept of valence electrons to be introduced. These are the electrons uncovered in the highest occupied power level or covering for an atom of an element. Because that our discussions us will emphasis on the facets in the an initial two columns ~ above the left-hand next of the periodic table and also the last six columns top top the right-hand next of the table. Together, these aspects are described as the main group or representative elements. Number 3.6 in Raymond provides Lewis electron dot structures to present the variety of valence electrons in few of the representative elements. Note that the number of valence electrons that each element has is same to its group number, e.g.

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, aspects in group IA have one valence electron (one dot), elements in group IIA have actually two valence electron (2 dots), etc.

Figure 1 (Figure 3.6 native Raymond): Valence Electrons. Representative aspects in the same team have the same number of valence electrons. In the electron period structures offered here, valence electron are presented as dots.


It transforms out that there is something distinct in nature about having eight electron in the valence shell. This happens be the many stable situation for an atom. The facets that have this number in your pure neutral develops are the facets in team VIIIA. This elements, together a group, space are dubbed the inert gases. All of the inert gases have actually 8 valence electrons, other than helium, which has actually 2. This is due to the fact that the very first energy level can only hold 2 electrons, whereas the other energy levels can hold 8 or an ext electrons. (Each energy level can contain approximately 2n electrons, whereby n is the energy level; refer to Section 3.2 and Table 3.4 in Raymond). Also if an power level deserve to hold an ext than 8 electrons, the many stable number, is 8. The inert gases are dubbed inert since they are really unreactive through themselves and also other elements. This reflects their high stability. Every one of the other elements on the routine table would like to be like an inert gas in regards to the number of electrons they have actually in your valence shell. aramuseum.orgistry deserve to be assumed of as basically a an effect of all of the facets on the routine table trying to accomplish the same variety of valence electron as among the inert gases. They carry out this by reacting v one another come gain, lose or re-superstructure electrons. So that each atom ends up v 8 electron in your valence shell. This is a explain of what is called the octet rule.

The periodic table reflects this situation. Initially the aspects were arranged on the periodic table, native left come right, follow to their atomic number, and also in columns follow to their aramuseum.orgical and also physical properties. For instance the far right-hand column includes gases which are all aramuseum.orgically inert. Number 3.8 in Raymond reflects the representative elements:

Figure 2 (Figure 3.8 indigenous Raymond): Some typical ions that representative elements. Atoms lose or acquire the number of electrons vital to have actually an octet (to end up being isoelectronic with the nearest inert gas). Here, isoelectronic ions and also atoms are presented with the exact same color.


The periodic table likewise provides clues about an element"s electronic structure. When focusing on the representative elements, the rows tell girlfriend which power level consists of the valence electrons: row 1 is the n=1 level, row 2 is the n=2 level, etc. The columns indicate, for the neutral form of the element, how many valance electrons room in the valance shell: the first column (Group IA) has 1 valence electron, the 2nd column (Group IIA) consists of 2 valence electrons, etc., and the last pillar (Group VIIIA) consists of 8 valence electrons.

The octet rule can be provided to predict the fee on the monoatomic ions that type from the representative elements. This is portrayed in figure 3.8. One of the means that atoms achieve 8 electrons in their valence covering is to shed or gain electrons. The aspects on the left-hand side of the routine table tend to shed electrons, these space the metals, if the facets on the right-hand side of the periodic table have tendency to obtain electrons, these are the non-metals. As soon as metals and also non-metals combine, the metals offer their valence electrons to the non-metals, so that each in the end has 8 electron in their outer power level. In the process, the metals type positive ion (cations), while the non-metals type negative ion (anions). Figure 3.8 reflects the Lewis electron dot structures for the usual ions developed by the representative elements. The non-metals, situated on the right-side the the periodic table, have each gained a number electrons same to their charge, and also as shown by the Lewis dot frameworks each has 8 electrons in their valence shell. The metals, located on the left-hand side of the regular table, have each lost a number of electrons same to their charge (now positive), and as displayed by the Lewis period structures, each has 0 electron left in your valence shell! The consequence of this is that the following lower power level, i beg your pardon is currently the highest occupied power level, will have 8 electron in the (Look at Table 3.4 in Raymond).

Atoms and also ions that share the very same number electron are claimed to it is in isoelectronic. Li+ is isoelectronic through He (2 electrons), and also this is presented by the red crate in figure 3.8; N3-, O2-, F-, Na+, Mg2+ and Al3+ room all isoelectronic through Ne (10 electrons) and this is displayed by the pink boxes in figure 3.8; and also P3-, S2-, Cl-, K+ and also Ca2+ room isoelectronic v Ar (18 electrons) and this is shown by the blue box in figure 3.8. Applications of the octet rule predicts that these are the ion that should kind from the representative elements.

Carbon (C) and also silicon (Si) are in group IVA. (See figure 3.2 of Raymond, i beg your pardon is also shown above.) facets in this group have 4 valence electrons. These facets could either get or lose 4 electron to become a monoatomic ion the is isoelectronic with an inert gas. However, since of the high fee that would result, either C4+ or C4- for carbon and Si4+ or Si4- for silicon, this is i can not qualify to happen. This is why they are not presented in the team IVA tower of number 3.8, displayed above. Us will watch that carbon uses an additional strategy because that adhering to the octet rule.

The octet rule does not occupational for predicting the charges on transition metals ions. Transition metals are situated on the routine table in the ten columns between columns IIA and IIIA for the representative elements, and also the teams are labeling IB to VIIIB. This is shown in figure 2.6 that Raymond:

Figure 3 (Figure 2.6 from Raymond): The periodic table the the elements. The periodic table is an organized list the the known elements. The names and atomic icons of the aspects are noted inside the front cover the Raymond"s text.


The transition metals commonly produce ions with 1+, 2+, 3+ and sometime 4+ charges, and unlike the representative aspects many transition metals deserve to have an ext than one fee state. An important example in bioaramuseum.orgistry is steel (Fe), i beg your pardon is commonly found in either a Fe2+ or Fe3+ state. Certain proteins dubbed electron transport proteins carry electrons by having actually bound iron ions cycle between a Fe2+ and Fe3+ states.

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The monoatomic ionic forms of both oxygen and also sulfur have actually a 2- charge (O2- and also S2-). Both oxygen and also sulfur room representative elements. Bases top top this information, suspect which teams oxygen and sulfur belong to.