Helium Lewis symbol

Notice how the Lewis symbols are presented in the following figure, and how the elements in each group have the same arrangement of valence electrons. The noble gases, except helium, have eight valence electrons, an octet of electrons. 

If a hydrogen atom were to gain a second electron, it would be isoelectronic with the stable electron configuration of helium. However, because two identical hydrogen atoms have an equal tendency to gain or lose electrons, an electron transfer from one atom to the other is unlikely to occur imder normal conditions. Each atom may attain a noble gas structure only by sharing its electron with the other, as shown with Lewis symbols ... 

The two electrons in the helium atom are shown by the Lewis symbol illustrated in Figure 3.5. These electrons constitute a filled electron shell, so that helium is a noble gas composed of individual helium atoms that have no tendency to form chemical bonds with other atoms. Helium gas has a very low density of only 0.164 g/L at 25°C and 1 atm pressure. 

Boron, B, has an atomic number of 5 and an atomic mass of 10.81. Most boron atoms have 6 neutrons in addition to 5 protons in their nuclei a less common isotope has 5 protons. Two of boron s 5 electrons are in a helium core and 3 are outer electrons, as shown by the Lewis symbol... 

Give the Lewis symbol of helium and explain what it has to do with... 

Helium is somewhat of an exception. Its electron configuration and Lewis symbol are ... 

Give the Lewis symbol of helium and explain what it has to do with (a) eleetron shell, (b) filled electron shell, (c) and noble gases. 

To show the outermost electrons of an atom, we commonly use a representation called a Lewis structure, after the American chemist Gilbert N. Lewis (1875-1946), who devised this notation. A Lewis structure shows the symbol of the element, surrounded by a number of dots equal to the number of electrons in the outer shell of an atom of that element. In Lewis structures, the atomic symbol represents the nucleus and all filled inner shells. Table 1.3 shows Lewis structures for the first 18 elements of the Periodic Table. As you study the entries in the table, note that, with the exception of helium, the number of valence electrons of the element corresponds to the group number of the element in the Periodic Table for example, oxygen, with six valence electrons, is in Group 6A. 

Except for helium, the number of valence electrons in an atom is the same as the group number of the element. For example, Li is a Group lA element and has one dot for one valence electron Be, a Group 2A element, has two valence electrons (two dots) and so on. Elements in the same group have similar outer electfon configurations and hence similar Lewis dot symbols. The transition metals, lanthanides, and actinides all have incompletely filled inner shells, so we generally cannot write simple Lewis dot symbols for them. 

This uses the Lewis electron-dot symbol for the hydrogen atoms and represents the covalent bond by a pair of dots. Recall that the two electrons from the covalent bond spend part of the time in the region of each atom. In this sense, each atom in H2 has a helium configuration. We can draw a circle about each atom to emphasize this. 

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