Nonmetals tend to gain electrons in order to achieve a full outer shell, so they are said to have high electronegativities.
Alkaline metals, for example, would find it much easier to lose electrons than gain electrons, so they are not very electronegative. On the other hand, halogens such as chlorine only need to gain one electron to form a full outer shell. This is much easier than losing seven electrons instead.
When it comes to transition metals it is a little more complicated, but like many other metals, they also have low electronegativities.
Transition metals have #(n-1)d# and #ns# orbitals which have many electrons similar in energy, meaning that it is sometimes easy for many of those electrons to be lost. This is also the reason why metals have a high electrical conductivity (i.e. their electrons are can easily move from atom to atom).
Answer
Verified
Hint: Ionic compounds are molecules that form through the gain and loss of electrons. A metal atom that loses an electron takes on a positive electric charge; a non-metal that gains an electron becomes negatively charged. Because opposite charges attract, the two atoms stick together, forming a strong, stable chemical bond.
Complete answer:
Elements can gain or lose electrons in order to attain their nearest noble gas configuration. Formation of ions for completion of
octet helps them gain stability. In a reaction between metals and nonmetals, metals generally lose electrons to complete their octet and non-metals gain electrons to complete their octet.
Metal atoms lose electrons from their outer shell when they form ions: the ions are positive, because they have more protons than electrons. The ions formed have full outer shells. The ions have the electronic structure of a noble gas (group zero element), with a full outer shell.
Nonmetals are further to
the right on the periodic table, and have high ionization energies and high electron affinities, so they gain electrons relatively easily, and lose them with difficulty. They also have a larger number of valence electrons, and are already close to having a complete octet of eight electrons.
Note:
Metals are good conductors of heat and electricity, and are malleable and ductile. Most of the metals are solids at room temperature, with a characteristic silvery shine (except for
mercury, which is a liquid). Nonmetals are (usually) poor conductors of heat and electricity, and are not malleable or ductile; many of the elemental nonmetals are gases at room temperature, while others are liquids and others are solids.
Learning Objectives
Most atoms do not have eight electrons in their valence electron shell. Some atoms have only a few electrons in their outer shell, while some atoms lack only one or two electrons to have an octet. 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. 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. Positively charged ions are called cations. Most metals become cations when they make ionic compounds.
Cations
A neutral sodium atom is likely to achieve an octet in its outermost shell by losing its one valence electron.
\[\ce{Na \rightarrow Na^{+} + e^{-}} \nonumber \]
The cation produced in this way, Na+, is called the sodium ion to distinguish it from the element. The outermost shell of the sodium ion is the second electron shell, which has eight electrons in it. The octet rule has been satisfied. Figure \(\PageIndex{1}\) is a graphical depiction of this process.
Anions
Some atoms have nearly eight electrons in their valence shell and can gain additional valence electrons until they have an octet. When these atoms gain electrons, they acquire a negative charge because they now possess more electrons than protons. Negatively charged ions are called anions. Most nonmetals become anions when they make ionic compounds.
A neutral chlorine atom has seven electrons in its outermost shell. Only one more electron is needed to achieve an octet in chlorine’s valence shell. (In table salt, this electron comes from the sodium atom.)
\[\ce{e^{-} +Cl -> Cl^{-}} \nonumber \]
In this case, the ion has the same outermost shell as the original atom, but now that shell has eight electrons in it. Once again, the octet rule has been satisfied. The resulting anion, Cl−, is called the chloride ion; note the slight change in the suffix (-ide instead of -ine) to create the name of this anion. Figure \(\PageIndex{2}\) is a graphical depiction of this process.
The names for positive and negative ions are pronounced CAT-eye-ons and ANN-eye-ons, respectively.
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. Thus, the periodic table becomes a tool for remembering the charges on many ions. For example, all ions made from alkali metals, the first column on the periodic table, have a 1+ charge. Ions made from alkaline earth metals, the second group on the periodic table, have a 2+ charge. On the other side of the periodic table, the next-to-last column, the halogens, form ions having a 1− charge. Figure \(\PageIndex{3}\) shows how the charge on many ions can be predicted by the location of an element on the periodic table. Note the convention of first writing the number and then the sign on a ion with multiple charges. The barium cation is written Ba2+, not Ba+2.