Table 2.3 Periodic table of the naturally‐occurring elements displaying atomic symbols, atomic number (Z), average mass, ground state electron configuration, common valence states and electronegativity of each element.
Simplified periodic table of the elements showing symbols atomic numbers and mass numbers |
Simplified periodic table of the elements showing symbols and electron configurations |
Simplified periodic table of the elements electronegativities common and valence states |
2.2.2 Ionization
The periodic table not only organizes the elements into rows based on their electron properties, but also into vertical columns based upon their tendency to gain or lose electrons to become more stable (Table 2.3). Ideal atoms are electrically neutral because they contain the same numbers of positively charged protons and negatively charged electrons (p+ = e−). Many atoms are not electrically neutral; instead they are electrically charged particles called ions. The process by which they acquire their charge is called ionization (Box 2.1). In order for an ion to form, the number of positively charged protons and negatively charged electrons must become unequal. Cations are positively charged ions because they have more positively charged protons than negatively charged electrons (p+ > e−). Their charge is equal to the number of excess protons (p+ − e−). Cations form when electrons are lost from the electron cloud. Ions that have more negatively charged electrons than positively charged protons, such as the ion chlorine (Cl− ), will have a negative charge and are called anions. The charge of an anion is equal to the number of excess electrons (e− − p+). Anions form when electrons are added to the electron cloud during ionization.
Box 2.1 Ionization energy
Ionization energy (IE) is the amount of energy required to remove an electron from its electron cloud. Ionization energies are periodic as illustrated for 20 elements in Table B2.1.
The first ionization energy is the amount of energy required to remove one electron from the electron cloud; the second ionization energy is the amount required to remove a second electron and so forth. Ionization energies are lowest for electrons that are weakly held by the nucleus and higher for electrons that are strongly held by the nucleus or are in stable configurations. Ionization energies decrease down the periodic table because the most weakly held outer electrons are shielded from the positively charged nucleus by a progressively larger number of intervening electrons. Elements with relatively low first ionization energies are called electropositive elements because they tend to lose one or more electrons and become positively charged cations. Most elements with high first ionization energies are electronegative elements because they tend to add electrons to their electron clouds and become negatively charged anions. Since opposite charges tend to attract, you can imagine the potential such ions have for combining to produce other Earth materials. The arrangement of elements into vertical columns or groups within the periodic table helps us to comprehend the tendency of specific atoms to lose, gain or share electrons. For example, on the periodic table (see Table 2.3), column 2 (IIA) elements commonly exist as divalent (+2) cations because the first and second ionization energies are fairly similar and much lower than the third and higher ionization energies. This permits two electrons to be removed fairly easily from the electron cloud, but makes the removal of additional electrons much more difficult. Column 13 (IIIA) elements commonly exist as trivalent (+3) cations (see Table 2.3). These elements have somewhat similar first, second and third ionization energies, which are much smaller than the fourth and higher ionization energies. The transfer of electrons is fundamentally important in the understanding of chemical bonds and the development of mineral crystals.
Table B2.1 Ionization energies for hydrogen through calcium (units in kJ/mole).
Element | Ionization energy | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
First | Second | Third | Fourth | Fifth | Sixth | Seventh | Eighth | ||||||||
H | 1312 |
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