Define ionic and molecular (covalent) compoundsPredict the type of compound developed from facets based on their place within the periodic tableDetermine formulas for straightforward ionic compounds

In plain chemical reactions, the nucleus of every atom (and therefore the identification of the element) stays unchanged. Electrons, however, can be added to atom by deliver from various other atoms, shed by move to various other atoms, or shared with various other atoms. The transfer and sharing the electrons among atoms govern the chemistry that the elements. During the formation of part compounds, atoms acquire or lose electrons, and type electrically charged particles referred to as ions (Figure 1).

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Figure 1. (a) A sodium atom (Na) has equal number of protons and electrons (11) and also is uncharged. (b) A sodium cation (Na+) has actually lost one electron, for this reason it has one much more proton (11) 보다 electrons (10), offering it an all at once positive charge, signified by a superscripted plus sign.

You can use the routine table to predict even if it is an atom will kind an anion or a cation, and also you can often predict the fee of the resulting ion. Atoms of numerous main-group steels lose enough electrons to leaving them with the same variety of electrons as an atom the the preceding noble gas. To illustrate, an atom of one alkali steel (group 1) loser one electron and forms a cation v a 1+ charge; an alkaline earth metal (group 2) loses two electrons and also forms a cation v a 2+ charge, and also so on. For example, a neutral calcium atom, with 20 protons and 20 electrons, easily loses 2 electrons. This results in a cation v 20 protons, 18 electrons, and also a 2+ charge. It has the same variety of electrons as atoms of the preceding noble gas, argon, and also is symbolized Ca2+. The name of a metal ion is the very same as the surname of the metal atom from which that forms, so Ca2+ is referred to as a calcium ion.

When atom of nonmetal elements form ions, they usually gain sufficient electrons to give them the same variety of electrons as an atom of the next noble gas in the regular table. Atoms of group 17 gain one electron and form anions through a 1− charge; atoms of team 16 get two electron and form ions through a 2− charge, and also so on. For example, the neutral bromine atom, through 35 protons and also 35 electrons, can gain one electron to provide it through 36 electrons. This results in an anion with 35 protons, 36 electrons, and also a 1− charge. It has the same variety of electrons as atoms of the following noble gas, krypton, and also is symbolized Br−. (A conversation of the theory sustaining the favored condition of noble gas electron numbers reflected in this predictive rules because that ion formation is listed in a later on chapter the this text.)

Note the usefulness the the routine table in predicting most likely ion formation and also charge (Figure 2). Relocating from the far left to the best on the periodic table, main-group facets tend to form cations with a charge equal to the team number. The is, team 1 elements form 1+ ions; team 2 elements kind 2+ ions, and also so on. Moving from the far right come the left top top the periodic table, aspects often form anions with a an adverse charge equal to the variety of groups relocated left indigenous the noble gases. Because that example, team 17 aspects (one group left the the noble gases) type 1− ions; group 16 elements (two teams left) form 2− ions, and also so on. This trend have the right to be offered as a overview in plenty of cases, yet its predictive worth decreases when relocating toward the facility of the routine table. In fact, transition metals and also some other metals often exhibit variable charges that space not predictable by their location in the table. Because that example, copper can type ions through a 1+ or 2+ charge, and iron can type ions with a 2+ or 3+ charge.

Figure 2. Some aspects exhibit a consistent pattern the ionic charge as soon as they type ions.

Example 1

Composition the IonsAn ion uncovered in part compounds provided as antiperspirants has 13 protons and 10 electrons. What is that symbol?

SolutionBecause the number of protons continues to be unchanged when an atom forms an ion, the atomic variety of the element must be 13. Understanding this allows us usage the periodic table to identify the aspect as Al (aluminum). The Al atom has actually lost 3 electrons and thus has actually three more positive fees (13) 보다 it has electrons (10). This is the aluminum cation, Al3+.

Check her LearningGive the symbol and also name for the ion with 34 protons and 36 electrons.

Example 2

Formation the IonsMagnesium and nitrogen reaction to kind an ionic compound. Suspect which creates an anion, which develops a cation, and also the charges of each ion. Compose the symbol for each ion and also name them.

SolutionMagnesium’s place in the periodic table (group 2) tells us that it is a metal. Metals kind positive ion (cations). A magnesium atom must shed two electron to have the very same number electrons together an atom the the ahead noble gas, neon. Thus, a magnesium atom will type a cation v two under electrons 보다 protons and also a charge of 2+. The symbol for the ion is Mg2+, and it is referred to as a magnesium ion.

Nitrogen’s place in the periodic table (group 15) reveals that it is a nonmetal. Nonmetals kind negative ion (anions). A nitrogen atom must gain three electron to have actually the same variety of electrons together an atom the the adhering to noble gas, neon. Thus, a nitrogen atom will kind an anion with three more electrons 보다 protons and also a fee of 3−. The symbol for the ion is N3−, and it is dubbed a nitride ion.

Check your LearningAluminum and carbon reaction to type an ionic compound. Suspect which creates an anion, which forms a cation, and also the dues of each ion. Write the symbol for each ion and also name them.


Al will type a cation v a charge of 3+: Al3+, an aluminum ion. Carbon will kind an anion with a charge of 4−: C4−, a carbide ion.

The ions that we have disputed so much are called monatomic ions, that is, they space ions created from only one atom. We likewise find countless polyatomic ions. This ions, i m sorry act together discrete units, are electrically charged molecules (a group of external inspection atoms through an overall charge). Few of the much more important polyatomic ions are noted in Table 6. Oxyanions space polyatomic ion that save on computer one or more oxygen atoms. At this suggest in your research of chemistry, you need to memorize the names, formulas, and also charges that the most common polyatomic ions. Because you will use them repeatedly, they will soon become familiar.

NameFormulaRelated AcidFormula
acetate\textCH_3\textCOO^-acetic acid\textCH_3\textCOOH
cyanide\textCN^-hydrocyanic acid\textHCN
azide\textN_3^\;\;-hydrazoic acid\textHN_3
carbonate\textCO_3^\;\;2-carbonic acid\textH_2\textCO_3
nitrate\textNO_3^\;\;-nitric acid\textHNO_3
nitrite\textNO_2^\;\;-nitrous acid\textHNO_2
sulfate\textSO_4^\;\;2-sulfiric acid\textH_2\textSO_4
hydrogen sulfate\textHSO_4^\;\;-
sulfite\textSO_3^\;\;2-sulfurous acid\textH_2\textSO_3
hydrogen sulfite\textHSO_3^\;\;-
phosphate\textPO_4^\;\;3-phosphoric acid\textH_3\textPO_4
hydrogen phosphate\textHPO_4^\;\;2-
dihydrogen phosphate\textH_2\textPO_4^\;\;-
perchlorate\textClO_4^\;\;-perchloric acid\textHClO_4
chlorate\textClO_3^\;\;-chloric acid\textHClO_3
chlorite\textClO_2^\;\;-chlorous acid\textHClO_2
hypochlorite\textClO^-hypochlorous acid\textHClO
chromate\textCrO_4^\;\;2-chromic acid\textH_2\textCr_2\textO_4
dichromate\textCr_2\textO_7^\;\;2-dichromic acid\textH_2\textCr_2\textO_7
permanganate\textMnO_4^\;\;-permanganic acid\textHMnO_4
Table 6. common Polyatomic Ions

Note that there is a mechanism for naming some polyatomic ions; -ate and also -ite room suffixes designating polyatomic ion containing much more or under oxygen atoms. Per- (short because that “hyper”) and hypo- (meaning “under”) room prefixes meaning more oxygen atoms 보다 -ate and also fewer oxygen atoms than -ite, respectively. Because that example, perchlorate is ClO4−, chlorate is ClO3−, chlorite is ClO2− and also hypochlorite is ClO−. Unfortunately, the number of oxygen atoms corresponding to a offered suffix or prefix is no consistent; for example, nitrate is NO3− while sulfate is SO42−. This will be covered in more detail in the next module ~ above nomenclature.

The nature that the attractive forces that hold atoms or ions with each other within a compound is the basis because that classifying chemical bonding. When electrons are transferred and also ions form, ionic bonds result. Ionic bonds room electrostatic pressures of attraction, the is, the attractive forces experienced between objects the opposite electrical charge (in this case, cations and anions). Once electrons space “shared” and molecules form, covalent bonds result. Covalent bonds are the attractive forces in between the positively charged nuclei that the bonded atoms and also one or much more pairs of electron that space located in between the atoms. Compounds are classified together ionic or molecule (covalent) on the communication of the bonds existing in them.

Ionic Compounds

When an element composed the atoms that readily lose electrons (a metal) reacts through an facet composed of atoms that readily get electrons (a nonmetal), a transfer of electrons commonly occurs, producing ions. The compound formed by this transport is stabilized through the electrostatic attractions (ionic bonds) in between the ions of opposite charge existing in the compound. Because that example, when each salt atom in a sample the sodium metal (group 1) provides up one electron to type a sodium cation, Na+, and also each chlorine atom in a sample that chlorine gas (group 17) accepts one electron to kind a chloride anion, Cl−, the resulting compound, NaCl, is written of sodium ions and chloride ions in the ratio of one Na+ ion because that each Cl− ion. Similarly, each calcium atom (group 2) can offer up 2 electrons and transfer one to each of 2 chlorine atom to form CaCl2, which is composed of Ca2+ and also Cl− ion in the proportion of one Ca2+ ion to two Cl− ions.

A link that includes ions and is hosted together through ionic bonds is referred to as an ionic compound. The regular table can aid us recognize numerous of the compound that room ionic: as soon as a steel is combined with one or much more nonmetals, the compound is usually ionic. This reminder works well because that predicting ionic compound formation for many of the compounds commonly encountered in an introductory chemistry course. However, it is not always true (for example, aluminum chloride, AlCl3, is not ionic).

You can often recognize ionic compounds due to the fact that of their properties. Ionic compounds are solids that typically melt in ~ high temperatures and boil in ~ even greater temperatures. For example, sodium chloride melts at 801 °C and boils in ~ 1413 °C. (As a comparison, the molecular compound water melts at 0 °C and boils in ~ 100 °C.) In hard form, one ionic link is not electrically conductive due to the fact that its ions are unable to flow (“electricity” is the circulation of fee particles). As soon as molten, however, it deserve to conduct electricity because its ions are able come move easily through the liquid (Figure 3).

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Figure 3. sodium chloride melts in ~ 801 °C and also conducts electrical energy when molten. (credit: modification of occupational by note Blaser and also Matt Evans)