2.7 Ions and Ionic Compounds


The nucleus of an atom is unchanged by plain chemical processes, yet atoms have the right to readily get or lose electrons. If electron are removed from or added to a neutral atom, a fee particle referred to as an ion is formed. An ion with a optimistic charge is called a cation (pronounced CAT-ion); a negatively charged ion is referred to as an anion (AN-ion). The salt atom, because that example, which has 11 protons and also 11 electrons, easily loses one electron. The result cation has actually 11 protons and also 10 electrons, so it has a net charge of

*
The net charge on an ion is stood for by a superscript;
*
*
and
*
median a net fee resulting from the lose of one, two, or three electrons, respectively. The superscripts
*
*
and also
*
represent net charges result from the get of one, two, or 3 electrons, respectively. The formation of the
*
ion indigenous an Na atom is displayed schematically together follows:


*


Chlorine, v 17 protons and 17 electrons, often gains one electron in chemical reactions, creating the

*
ion.

You are watching: What is the charge on the most stable ion of each of the following elements?


*


In general, steel atoms often tend to lose electrons to kind cations, vice versa, nonmetal atoms tend to obtain electrons to kind anions.


SAMPLE practice 2.7

Give the chemistry symbols, consisting of mass numbers, for the adhering to ions: (a) The ion v 22 protons, 26 neutrons, and also 19 electrons; (b) the ion of sulfur that has 16 neutrons and also 18 electrons.

Solution

(a) The variety of protons (22) is the atomic variety of the element, for this reason the aspect is Ti (titanium). The mass number of this isotope is

*
(the sum of the protons and neutrons). Due to the fact that the ion has three much more protons than electrons, it has actually a net charge of
*
Thus, the symbol because that the ion is
*

(b) By referring to a periodic table or table that elements, we check out that sulfur (symbol S) has an atomic number of 16. Thus, each atom or ion of sulfur has actually 16 protons. We space told the the ion likewise has 16 neutrons, so the mass variety of the ion is

*
due to the fact that the ion has actually 16 protons and also 18 electrons, that net charge is
*
Thus, the finish symbol for the ion is
*

In general, us will focus on the network charges of ions and ignore your mass numbers unless the scenarios dictate that we specify a particular isotope.

PRACTICE EXERCISE

How many protons and electrons go the

*
ion possess?

Answer: 34 protons and also 36 electron


In addition to straightforward ions such as Na+ and Cl-, there are polyatomic ions such as NO3- (nitrate ion) and also SO42- (sulfate ion). These ion consist of atoms joined as in a molecule, however they have a net optimistic or negative charge. We will think about further instances of polyatomic ion in ar 2.8.

The chemical properties of ion are very different from those the the atom from i beg your pardon they room derived. The distinction is favor the adjust from Dr. Jekyll to Mr. Hyde: back the body may be essentially the very same (plus or minus a few electrons), the behavior is lot different.

Predicting Ionic Charges

Many atoms get or lose electrons so regarding end up through the same number of electrons together the noble gas closest come them in the periodic table. The members the the noble-gas family are chemically very nonreactive and kind very few compounds. We could deduce the this is due to the fact that their electron kinds are really stable. Adjacent elements can acquire these exact same stable kinds by losing or acquiring electrons. Because that example, ns of one electron indigenous an atom of sodium leaves it through the same variety of electrons together the neutral neon atom (atomic number 10). Similarly, as soon as chlorine gains an electron, it ends up v 18, the same as argon (atomic number 18). We will use this an easy observation to explain the development of ion in chapter 8, whereby we talk about chemical bonding.

The routine table is an extremely useful because that remembering the charges of ions, particularly those that the elements on the left and also right sides of the table. As figure 2.22 shows,


*

Figure 2.22 fees of some typical ions uncovered in ionic compounds. An alert that the steplike line the divides steels from nonmetals likewise separates cations native anions.


SAMPLE practice 2.8

Predict the charges meant for the most stable ions of barium and also oxygen.

Solution

We will certainly assume that these elements form ions that have the same number of electrons as the nearest noble-gas atom. From the periodic table, barium has actually atomic number 56. The nearest noble gas is xenon, atomic number 54. Barium can attain a stable setup of 54 electrons by losing two that its electrons, developing the

*
cation.

Oxygen has actually atomic number 8. The nearest noble gas is neon, atomic number 10. Oxygen can obtain this steady electron setup by acquiring two electrons, thereby forming the

*
anion.

PRACTICE EXERCISE

Predict the fee of the most stable ion that aluminum.

Answer: 3+


The periodic table is really useful because that remembering the fees of ions, particularly those that the elements on the left and also right political parties of the table. As figure 2.22 shows, the charges of these ions relate in a simple method to their positions in the table. ~ above the left side of the table, because that example, the group 1A aspects (the alkali metals) type 1+ ions, and also the group 2A facets (the alkaline earths) form 2+ ions. Top top the various other side the the table the group 7A facets (the halogens) type 1- ions, and also the group 6A elements form 2- ions. As we will see later on in the text, many of the other groups do not lend themselves to such simple rules.

Ionic Compounds

A great deal of chemical activity involves the transport of electrons between substances. Ions kind when one or an ext electrons transfer from one neutral atom come another. Number 2.23 shows that once elemental sodium is permitted to react through elemental chlorine, an electron move from a neutral salt atom to a neutral chlorine atom. We space left through an Na+ ion and also a Cl- ion. Objects the opposite fee attract, however, so the Na+ and the Cl- ions bind together to form the compound sodium chloride (NaCl), which us know better as common table salt. Sodium chloride is an instance of one ionic compound, a compound that contains both positively and negatively fee ions.


*

Figure 2.23 (a) The carry of an electron native a neutral Na atom to a neutral Cl atom leads to the development of one Na+ ion and a Cl- ion. (b) setup of these ion in solid salt chloride (NaCl) is pictured in ~ the right.


We can often tell even if it is a link is ionic (consisting that ions) or molecule (consisting that molecules) native its composition. In general, cations are metal ions, conversely, anions space nonmetal ions. Consequently, ionic compounds are normally combinations the metals and also nonmetals, as in NaCl. In contrast, molecular compounds are generally composed of nonmetals only, as in H20.


SAMPLE practice 2.9

Which that the adhering to compounds would certainly you intend to it is in ionic:

*
*
*
*

Solution

We would certainly predict that

*
and
*
are ionic compounds since they are composed that a metal combined with a nonmetal. The other two compounds, composed completely of nonmetals, room predicted (correctly) come be molecule compounds.

PRACTICE EXERCISE

Which the the complying with compounds room molecular:

*
FeS,
*
*

Answer: CBr4 and P4O6


The ions in ionic compounds space arranged in three-dimensional structures. The setup of Na+ and also Cl- ion in NaCl is presented in figure 2.23. Because there is no discrete molecule the NaCl, we are able come write just an empirical formula for this substance. In fact, only empirical formulas deserve to be created for most ionic compounds.

We can readily create the empirical formula because that an ionic compound if we recognize the dues of the ions of which that is composed. Chemistry compounds are always electrically neutral. Consequently, the ions in one ionic compound constantly occur in together a proportion that the total positive charge amounts to the total negative charge. Thus, over there is one Na+ come one Cl- (giving NaCl), one Ba2+ to 2 Cl- (giving BaCl2), and so forth.

See more: How Many Protons Does Zinc Have, How Many Neutrons, Protons, And Electrons In Zinc

As you think about these and also other examples, girlfriend will watch that if the dues on the cation and anion are equal, the subscript on each ion will be 1. If the charges space not equal, the charge on one ion (without the sign) will come to be the subscript top top the other ion. For example, the ionic compound developed from Mg (which creates Mg2+ ions) and also N (which forms N3- ions) is Mg3N2:

formula come come


SAMPLE exercise 2.10

What are the empirical recipe of the compounds developed by (a)

*
and
*
ions; (b)
*
and
*
ions; (c)
*
and
*
ions?

Solution

(a) 3

*
ion are compelled to balance the charge of one
*
ion. Thus, the formula is
*

(b) 2

*
ions are compelled to balance the charge of three
*
ion (that is, the total positive fee is
*
and the total an adverse charge is
*
). Thus, the formula is
*

(c) 2

*
ions are needed to balance the fee of one
*
hence the formula is
*
In this case the formula because that the entire polyatomic ion
*
must be attached in bracket so that it is clear that the subscript 2 applies to every the atom of that ion.

PRACTICE EXERCISE

Write the empirical formulas for the compounds developed by the complying with ions: (a)

*
and also
*
(b)
*
and
*
(c)
*
and also
*