Outermost electrons symbolism

The electron configuration is the orbital description of the locations of the electrons in an unexcited atom. Using principles of physics, chemists can predict how atoms will react based upon the electron configuration. They can predict properties such as stability, boiling point, and conductivity. Typically, only the outermost electron shells matter in chemistry, so we truncate the inner electron shell notation by replacing the long-hand orbital description with the symbol for a noble gas in brackets. This method of notation vastly simplifies the description for large molecules. 

Before looking at molecules, we need to review the structure of atoms. Most of the mass of an atom is concentrated in the nucleus. The nucleus consists of protons, which are positively charged, and neutrons, which are neutral. To counterbalance the charge on the nucleus due to the positive protons, the atom has an equal number of negative electrons in shells or orbitals around the nucleus. Because the electrons in the outermost electron shell (the valence electrons) control how the atom bonds, atoms are often represented by their respective atomic symbol surrounded by dots representing the outer-shell electrons. Such representations for some of the elements of interest to us are shown in Figure 1.1. The number of electrons in the valence shell of an atom is the same as the group number of that atom in the periodic table. 

The shared electron-pair is such a fundamental concept of chemical bonding that it is important to have a simple way of writing out a formula that shows the disposition of the shared pairs between the different atoms. This is commonly accomplished by depicting the valence (outermost) electrons of an atom as dots that are written around the atom symbols. Sometimes it is convenient to represent the electrons that are contributed by different atoms by different symbols. For example, the formation of H2 can be depicted as... 

To represent the formation of bonds between atoms, it is convenient to use a system known as electron dot notation. In this notation, the symbol for an element is used to represent the nucleus of an atom of the element plus all the electrons except those in the outermost (valence) shell. The outermost electrons are represented by dots (or tiny circles or crosses). For example, the dot notations for the first 10 elements in the periodic table are as follows ... 

Chemical bonding usually involves only the outermost electrons of atoms, also called valence electrons. In Lewis dot representations, only the electrons in the outermost occupied r and p orbitals are shown as dots. Paired and unpaired electrons are also indicated. Table 7-1 shows Lewis dot formulas for the representative elements. All elements in a given group have the same outer-shell electron configuration. It is somewhat arbitrary on which side of the atom symbol we write the electron dots. We do, however, represent an electron pair as a pair of dots and an unpaired electron as a single dot. 

Electron configurations are often written to emphasize the outermost electrons. This is done by writing the symbol in brackets for the element with a full p subshell from the previous shell and adding the outer electron configuration onto that configuration. 

The symbol [Ne] represents the electron configuration of the ten electrons of neon, ls 2s 2p . Writing the electron configuration as [Ne]3s focuses attention on the outermost electron of the atom, which is the one largely responsible for how sodium behaves chemically. 

INTRODUCTION AND SECTION 8.1 In this chapter we have focused on the interactions that lead to the formation of chemical bonds. We classify these bonds into three broad groups ionic bonds, which result from the electrostatic forces that exist between ions of opposite charge covalent bonds, which result from the sharing of electrons by two atoms and metallic bonds, which result fiom a delocalized sharing of electrons in metals. The formation of bonds involves interactions of the outermost electrons of atoms, their valence electrons. The valence electrons of an atom can be represented by electron-dot symbols, called Lewis symbolSL The tendencies of atoms to gain, lose, or share their valence electrons often follow the octet ruie, which can be viewed as an attempt by atoms to achieve a noble-gas electron configuration. 

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. 

The electronic structure of an atom may be represented by an electron-dot symbol, in which the electrons of the outer shell (or outer octet) are represented by dots and the nucleus and inner electrons by the chemical symbol of the element. The electron-dot symbol of lithium, Li-, shows only the outermost electron, which is called the valence electron. 

The electrons are shown being introduced in sequence the first and second in the Kv orbital, the next two in the Is orbital, the next six in the 2p orbitals, and so on. The sequence is indicated by arrows. The symbol and atomic number of each element are shown adjacent to the outermost electron (least tightly held electron) in the neutral atom. 

As a simple example, an atom with only one unpaired electron, consider a ground state sodium atom (11 electrons). This has a full n — shell, a full n — 2 shell and the single outermost electron in a n = 3 i-orbital, i.e. I = 0. The fuU shells have zero spin and angular momenta and therefore do not contribute to the term symbol, which, since S = and L — 0,is Si/2 (read as doublet S one half). If the electron is excited into an n = 3 p-orbital, then since S = V2, L = 1 the spin and angular momenta can reinforce or oppose each other giving J = (2 or (2 to give two term symbols P3/2 and Pi/2 (read as doublet P three halves, doublet P one half) see Fig. 1.8 for a diagram of this case). These two levels with J = 1 ... 

The first two electrons in a given principal level are always in the s sublevel and are together (paired) in the same orbital, the spherical s orbital. Recalling Hund s rule from this same discussion, electrons in the p sublevel do not pair up until after all three orbitals get an electron. Lewis structures use the element symbol with dots around the symbol to characterize the outermost electron level of that element. If you imagine the symbol enclosed in a square, each of the four sides of the square represents an orbital. Thus one side of the square represents an s orbital and the other three sides represent p orbitals within the outermost level. See Figure 6.1. Which side we use to represent... 

In the symbol for the sodium ion, the ionic charge of 1+ is written in the upper right-hand comer, Na, where the 1 is understood. The sodium ion is smaller than the sodium atom because the ion has lost its outermost electron from the third energy level. The positively charged ions of metals are called cations (pronounced cat-eye-uns) and use the name of the element. 

Valence electrons When elements combine chemically, only the electrons in the highest principal energy level of each atom are involved. Therefore, these outermost electrons, called valence electrons, determine most of the chemical properties of an element. Later in your chemistry course, you will study the way in which elements form chemical bonds. Because bonding involves an atom s valence electrons, it is useful to be able to sketch a representation of an element s valence electrons. The American chemist G. N. Lewis devised the electron-dot structure to show an atom s valence electrons by writing dots around the symbol of the element. 

This idea is readily extended to simple molecules of compounds formed by nonmetal atoms. An example is the HF molecule. You will recall that a fluorine atom has the electron configuration ls22s22p5. ft has seven electrons in its outermost principal energy level (n = 2). These are referred to as valence electrons, in contrast to the core electrons filling the principal level, n = 1. If the valence electrons are shown as dots around the symbol of the element, the fluorine atom can be represented as... 

Fig. 1.8. Dalton s atoms and the electronic states in an atom. A, a chart in Dalton s A New System of Chemical Philosophy, published in 1808. In modern symbols, these atoms are 1, H 2, N 3, C 4, O 5, P 6, S 7, Mg 8, Ca 9, Na 10, K 11, Sr 12, Ba 13, Fe 14, Zn 15, Cu 16, Pb 17, Ag 18, Pt 19, Au 20, Hg. The major modem modification to Dalton s theory is that the atoms are divisible. The contour maps in B represent typical electronic states in atoms. The outermost contour on each map represents a density of 10 A The successive contours rcpre.sent an increase of a factor of 2. The regions with dashed-curve contours have opposite phases in the wavefunction from those with solid-curve contours.

Electrons in the outermost occupied shell of any atom may play a significant role in that atoms chemical properties, including its ability to form chemical bonds. To indicate their importance, these electrons are called valence electrons (from the Latin valentia, strength ), and the shell they occupy is called the valence shell. Valence electrons can be conveniently represented as a series of dots surrounding an atomic symbol. This notation is called an electron-dot structure or, sometimes, a Lewis dot symbol, in honor of the American chemist G. N. Lewis, who first proposed the concepts of shells and valence electrons. Figure 6.2 shows the electron-dot structures for the atoms important in our discussions of ionic and covalent bonds. (Atoms of elements in groups 3 through 12 form metallic bonds, which we ll study in Chapter 18.)... 

In the case of writing the electron distribution of the elements after neon, we can start with the [Ne] symbol and then write the electrons in the last (outermost) shell. 

Lewis Symbol or Electron Dot Symbol Such a symbol marks the number of electrons in the outermost shell of the element around the symbol of the element , e.g. 

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