Its first two shells are full, and the remaining shells are empty. Helium, for instance, has a completely full inner shell, and all of its other shells are completely empty. These elements, called the noble gases, are happy just the way they are. Thus, elements toward the left side of the periodic table ( metals) tend to give away valence electrons, while elements toward the right side ( non-metals) tend to collect them. On the other hand, elements toward the right side of the periodic table, like oxygen and fluorine, find it easier to fill their shells (by adding an extra electron or two) rather than getting rid of their many valence electrons. Giving away two is much easier than collecting sixteen, of course, so calcium strongly prefers to give its two valence electrons away. Well, you don’t have to be a lithium atom to know that giving one electron away is much easier than begging your friends for seven of theirs! Similarly, the element calcium (the second element in the fourth row) could either give away its two valence electrons to empty its fourth shell, or collect sixteen more to fill that shell. To avoid the disgrace of having a partly-filled shell, lithium could either give away its valence electron (thereby emptying its second shell) or collect seven more (to fill that shell, which can hold eight). These elements are eager to give away that valence electron in a chemical reaction. It’s a noble gas, so it has no partly-filled shells and therefore no valence electrons.Ītoms of hydrogen and the alkali metals, which are listed in the first column of the periodic table, each have one valence electron. How many valence electrons does neon have? None. Since it’s the first element in its row, it has just one valence electron. How many valence electrons does sodium have? Sodium is the first element in the third row. (Notice that a number of columns are skipped when counting across the second row, because those columns don’t have any elements for this row.) Since it is the sixth element in its row, it has six valence electrons. The barium cation is written Ba 2+, not Ba +2.How many valence electrons does an oxygen atom have? Oxygen is the sixth element in the second row. Note the convention of first writing the number and then the sign on a multiply charged ion. Figure 3.3 “Predicting Ionic Charges” shows how the charge on many ions can be predicted by the location of an element on the periodic table. On the other side of the periodic table, the next-to-last column, the halogens, form ions having a 1− charge. Ions made from alkaline earth metals, the second group on the periodic table, have a 2+ charge. For example, all ions made from alkali metals, the first column on the periodic table, have a 1+ charge. Thus, the periodic table becomes a tool for remembering the charges on many ions. In many cases, elements that belong to the same group (vertical column) on the periodic table form ions with the same charge because they have the same number of valence electrons. In macroscopic samples of sodium chloride, there are billions and billions of sodium and chloride ions, although there is always the same number of cations and anions. The number of electrons lost by the sodium atom (one) equals the number of electrons gained by the chlorine atom (one), so the compound is electrically neutral. Notice that there are no leftover electrons. The resulting combination is the compound sodium chloride. With two oppositely charged ions, there is an electrostatic attraction between them because opposite charges attract. On the right, the chloride ion has 18 electrons and has a 1− charge. Most nonmetals become anions when they make ionic compounds.įigure 3.2 The Formation of a Chlorine Ion. On the left, the chlorine atom has 17 electrons. Negatively charged ions are called anions. When these atoms gain electrons, they acquire a negative charge because they now possess more electrons than protons. Some atoms have nearly eight electrons in their valence shell and can gain additional valence electrons until they have an octet. Most metals become cations when they make ionic compounds. Positively charged ions are called cations. Atoms that lose electrons acquire a positive charge as a result because they are left with fewer negatively charged electrons to balance the positive charges of the protons in the nucleus. In cases where an atom has three or fewer valence electrons, the atom may lose those valence electrons quite easily until what remains is a lower shell that contains an octet. Some atoms have only a few electrons in their outer shell, while some atoms lack only one or two electrons to have an octet. Most atoms do not have eight electrons in their valence electron shell.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |