A "normal" atom is one whose electric charge is neutral; that is, it has the same number of negatively charged electrons and positively charged protons, so the total charge is zero. However, when this atom loses or gains electrons, it acquires an electrical charge. Positive ions (cations) and negative ions (anions) can join together to form ionic compounds that, again, have a neutral electrical charge. To name ionic compounds, strict rules must be followed. This way, after learning them, you can always write the chemical formula of the compound.
In case you know the formula of an ionic compound and want to know what its name is in words, you can read about how to name ionic compounds instead.
Steps
Method 1 of 3: Write Formulas for Simple Binary Compounds
Step 1. Identify a binary compound
The simplest ionic compounds are those that are made up of exactly two elements, one metallic and one non-metallic. The compound must always be named by writing the names of the two elements and adding the suffix "uro" to the name of the nonmetal (except when the nonmetal is oxygen, in which case it must be written as "oxide").
- Some examples of simple binary ionic compounds are potassium oxide and sodium phosphide.
- In case the suffix "uro" does not come after the name of a single element, you should investigate what the instructions are for polyatomic ions. For example, "oxide" is a simple oxygen ion, while "hydroxide" and "peroxide" are polyatomic ions.
Step 2. Find both elements on the periodic table
The second element in the name refers to the metal ion (the cation positively charged). You can find this element on the left side of the periodic table. The first element, which has the suffix "uro", is a non-metallic ion (the anion negatively charged). You can find it on the right side of the periodic table.
For example, potassium oxide is a combination of potassium (whose chemical symbol is K and its atomic number is 19) and oxygen (symbol O, atomic number 8). Note that the suffix "gone" in this case is not part of the element name. Therefore, you only have to look for an element that begins in the same way ("ox", in this case)
Step 3. Find the charge of each ion
In the case of simple compounds, it is easy to predict the charge of each of the ions. The elements in each particular column of the periodic table always form ions that have the same charge:
- The elements Li, Na, K, Rb and Cs of group 1 acquire a charge of 1+ (which is written as just +).
- The elements Mg, Ca, Sr and Ba of group 2 acquire a charge of 2+.
- Element Al of group 13 acquires a charge of 3+.
- The elements N and P of group 15 acquire a charge of 3-.
- The elements O and S of group 16 acquire a charge of 2-.
- The elements F, Cl, Br ex I of group 17 acquire a charge of 1- (which is written as -).
Step 4. Balance the loads
Ionic compounds are held together by electrical forces, which attract positive and negative ions to each other. The ionic compound, as a whole, is electrically neutral, which means that its total charge is zero. (If it had a different charge, it would attract another atom.) You must find the number of atoms of each element that join together to "cancel" the charge of the other element and make the compound neutral.
-
For example, potassium oxide is made up of potassium ions K + { displaystyle K ^ {+}}
y oxígeno O2−{displaystyle O^{2-}}
, lo que significa que dos iones de potasio (cuya carga total es de 2+) equilibran la carga de un ion de oxígeno (cuya carga es de 2-).
- Este es un atajo: la carga del primer ion (sin importar los signos + o -) te brinda información sobre la cantidad de átomos del segundo ion y viceversa. Por ejemplo, el fluoruro de aluminio está conformado por los iones Al3+{displaystyle Al^{3+}}
y F−{displaystyle F^{-}}
. Al3+{displaystyle Al^{3+}}
tiene una carga de 3, por lo que hay 3 átomos de F−{displaystyle F^{-}}
. F−{displaystyle F^{-}}
tiene una carga de 1, por lo que hay 1 átomo de Al3+{displaystyle Al^{3+}}
Step 5. Write your answer in the form of a chemical formula
Write both chemical symbols starting with the second element in the name (metal first, then nonmetal). After each of them, you must write the number of atoms in the form of a subscript (asi { displaystyle _ {asi}}
). En caso de que haya exactamente un átomo de un elemento, no es necesario escribir un número. Tampoco debes escribir las cargas.
- Por ejemplo, el óxido de potasio tiene dos átomos de potasio y uno de oxígeno, por lo que su fórmula química es K2O{displaystyle K_{2}O}
- El fluoruro de aluminio tiene un átomo de aluminio y tres de fluoruro, por lo que su fórmula química es AlF3{displaystyle AlF_{3}}
Step 6. Simplify if possible
The formulas of ionic compounds are always written with the minimum number of atoms that are necessary. In case it is possible to balance the charges with fewer atoms, you should rewrite the formula. This process is the same as the reduction of fractions.
-
For example, barium sulfide is made up of the ions Ba2 + { displaystyle Ba ^ {2+}}
y S2−{displaystyle S^{2-}}
. Mediante el atajo mencionado anteriormente, la carga del ion de bario (2) es igual a la cantidad de iones de sulfuro, mientras que la carga del ion de sulfuro (2) es igual a la cantidad de iones de bario. De esta forma, obtenemos la fórmula Ba2S2{displaystyle Ba_{2}S_{2}}
. Sin embargo, no se necesitan tantos átomos para equilibrar las cargas, por lo que puedes escribir ambos números como una fracción y simplificarla: 2 atomos de bario2 atomos de azufre=11{displaystyle {frac {2\ atomos\ de\ bario}{2\ atomos\ de\ azufre}}={frac {1}{1}}}
. Por tanto, la fórmula correcta es BaS{displaystyle BaS}
Método 2 de 3: Compuestos binarios con metales de transición
Step 1. Find the Roman numeral in the compound name
Most of the elements found in "block d" of the periodic table (groups 3 through 12) are considered transition metals. Unlike what happens with the other elements, these can form ions of various types. If a transition metal is part of an ionic compound, a Roman numeral is included to specify the ion that makes it up.
For example, sometimes copper forms an ion with a +1 charge and sometimes with a +2 charge. The ionic compounds copper (I) chloride and copper (II) chloride are different. The Roman numeral indicates which is the copper ion that is part of that compound
Step 2. Find the charge of the cation
The second word in the compound's name represents the metal ion or cation, which always has a positive charge. You just have to add the Roman numeral as a positive charge to the name of the element:
-
For example, copper (II) chloride contains the cation Cu2 + { displaystyle Cu ^ {2+}}
, ya que el número romano II quiere decir 2.
Step 3. Find the charge of the anion
The first word of the compound name represents the anion; that is, the negatively charged ions that are formed from non-metallic elements. Elements of this type can only form one ion. Therefore, to find out what the charge of that ion is, you can look it up in a chemistry textbook or website, or memorize the rules mentioned above for groups.
-
For example, the ion of chlorine is called chloride. Chlorine, like the like elements in Group 17, forms ions with a charge of -1, which is written as Cl - { displaystyle Cl ^ {-}}
Step 4. Balance the loads
This is the same process for all ionic compounds. The total positive charge of the cations must always balance the total negative charge of the anions and the net charge of the ionic compound is always zero.
-
If you want to balance a 2+ charge of an ion of Cu2 + { displaystyle Cu ^ {2+}}
, serán necesarios dos iones de Cl−{displaystyle Cl^{-}}
(dos iones x una carga de -1 por ion = -2). De esta forma, obtienes un compuesto iónico cuya carga neta es de +2 -2 = 0.
Step 5. Write the chemical formula
As always, you should write the number of atoms as a subscript after the element symbol. There is no need to write the charges in the final formula.
-
Copper (II) chloride has one atom of copper and two of chlorine. Therefore, its formula is CuCl2 { displaystyle CuCl_ {2}}
Método 3 de 3: Compuestos con iones poliatómicos
Step 1. Understand polyatomic ions
Sometimes several elements can come together and form an ion. This ion can then combine with another to form a compound. For example, OH − 1 { displaystyle OH ^ {- 1}}
es un ion poliatómico que está conformado por iones de oxígeno e hidrógeno. Cada ion poliatómico tiene un nombre especial. Por ejemplo, al ion OH−1{displaystyle OH^{-1}}
it is called
-
OH − 1 { displaystyle OH ^ {- 1}}
, which contains two oxygen atoms but whose total charge is -2. (This is not the same as oxide, ion" estándar"="" de="" oxígeno,="" el="" cual="" tiene="" un="" solo="" átomo="" con="" una="" carga="" de=" />
Step 2. Find the chemical formula for the polyatomic ion
The first word of the ionic compound name represents the polyatomic ion. Therefore, you must search for this word (but not the full name of the compound) to find the formula for the polyatomic ion. You can also memorize several common polyatomic ions:
-
cyanide: CN - { displaystyle CN ^ {-}}
(un átomo de carbono y uno de nitrógeno con una carga total de -1)
- hidróxido: OH−{displaystyle OH^{-}}
- nitrato: NO3−{displaystyle NO_{3}^{-}}
- nitrito: NO2−{displaystyle NO_{2}^{-}}
- peróxido: O22−{displaystyle O_{2}^{2-}}
- sulfato: SO42−{displaystyle SO_{4}^{2-}}
- sulfito: SO32−{displaystyle SO_{3}^{2-}}
(un átomo de nitrógeno y tres de oxígeno con una carga total de -1)
Step 3. Find the charge of the other ion
The other ion in the compound is usually a simple one-atom ion. To find its load, you can do it in the same way as for any problem.
-
For example, magnesium hydroxide contains a magnesium cation. This element belongs to group 2 and forms the ion Mg2 + { displaystyle Mg ^ {2+}}
Step 4. Balance the charges of both ions
All ionic compounds have a net total charge of zero. You must find what is the minimum amount of positive and negative ions that perfectly balance the opposite charge. Don't forget that a polyatomic ion makes up a single ion, so you can't divide it into parts.
-
For example, if you want to balance OH − 1 { displaystyle OH ^ {- 1}}
y Mg2+{displaystyle Mg^{2+}}
, debes comparar las cargas. Para equilibrar una carga de 2+ se necesitan dos cargas de -1, por lo que habrá dos iones de hidróxido y uno de magnesio.
Step 5. Write the formula
If you want to denote that there is more than one polyatomic ion, you must put that part of the formula in parentheses. Then write the number of atoms in the form of a subscript after the closing parentheses.
-
For example, the chemical formula for magnesium hydroxide is Mg (OH) 2 { displaystyle Mg (OH) 2}
- No es necesario incluir las cargas de los iones.
Consejos
- Existen dos metales de transición que son más coherentes que los demás y solo forman un tipo de ion. La plata siempre forma el ion Ag+{displaystyle Ag^{+}}
y el zinc siempre forma el ion Zn2+{displaystyle Zn^{2+}}
. Therefore, since there is only one possible type of ion, it is not necessary to use a Roman numeral for compounds containing these elements. </li>
<li> You may see compound names with the suffixes in outdated or outdated textbooks" oso"="" e="" "ico"="" en="" lugar="" del="" nombre="" regular="" de="" un="" metal="" de="" transición="" y="" su="" número="" romano.="" la="" versión="" con="" el="" sufijo="" "oso"="" siempre="" hace="" referencia="" al="" ion="" con="" la="" carga="" menor,="" mientras="" que="" la="" versión="" con="" el="" sufijo="" "ico"="" hace="" referencia="" al="" ion="" con="" la="" carga="" mayor.="" por="" ejemplo,="" a="" los="" iones="" cromo="" (ii)="" y="" cromo="" (iii)="" se="" les="" solía="" llamar="" "cromoso"="" y="" "crómico",=" />