Define ionic and also molecular (covalent) compoundsPredict the type of compound created from elements based ~ above their ar within the periodic tableDetermine recipe for straightforward ionic compounds

In simple chemical reactions, the nucleus of every atom (and therefore the identification of the element) remains unchanged. Electrons, however, can be added to atoms by move from other atoms, lost by move to various other atoms, or shared with other atoms. The transfer and also sharing the electrons amongst atoms administrate the chemistry that the elements. Throughout the formation of part compounds, atoms get or lose electrons, and kind electrically charged particles referred to as ions (Figure 1).

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Figure 1. (a) A salt atom (Na) has actually equal numbers of protons and also electrons (11) and is uncharged. (b) A sodium cation (Na+) has actually lost an electron, so it has actually one an ext proton (11) than electrons (10), providing it an overall positive charge, signified by a superscripted plus sign.

You have the right to use the periodic table come predict even if it is an atom will kind an anion or a cation, and you can frequently predict the fee of the result ion. Atoms of plenty of main-group steels lose enough electrons to leave them v the same number of electrons together an atom of the coming before noble gas. Come illustrate, an atom of an alkali metal (group 1) loses one electron and forms a cation with a 1+ charge; one alkaline earth metal (group 2) loses two electrons and forms a cation v a 2+ charge, and also so on. Because that example, a neutral calcium atom, with 20 protons and also 20 electrons, readily loses two electrons. This outcomes in a cation v 20 protons, 18 electrons, and a 2+ charge. It has actually the same variety of electrons together atoms the the preceding noble gas, argon, and is symbolized Ca2+. The surname of a steel ion is the exact same as the name of the metal atom native which the forms, therefore Ca2+ is referred to as a calcium ion.

When atoms of nonmetal elements type ions, they usually gain enough electrons to offer them the same number of electrons as an atom the the following noble gas in the routine table. Atoms of group 17 obtain one electron and type anions v a 1− charge; atom of team 16 get two electron and kind ions v a 2− charge, and so on. Because that example, the neutral bromine atom, through 35 protons and 35 electrons, can get one electron to carry out it through 36 electrons. This outcomes in an anion v 35 protons, 36 electrons, and also a 1− charge. It has actually 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 standing of noble gas electron number reflected in this predictive rules for ion formation is provided in a later chapter of this text.)

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

Figure 2. Some aspects exhibit a constant pattern that ionic charge as soon as they type ions.

Example 1

Composition of IonsAn ion uncovered in some compounds provided as antiperspirants contains 13 protons and 10 electrons. What is that is symbol?

SolutionBecause the variety of protons continues to be unchanged as soon as an atom develops an ion, the atomic variety of the element must be 13. Knowing this lets us usage the regular table to recognize the aspect as Al (aluminum). The Al atom has actually lost 3 electrons and also thus has actually three much more positive dues (13) 보다 it has actually electrons (10). This is the aluminum cation, Al3+.

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

Example 2

Formation the IonsMagnesium and nitrogen reaction to form an ionic compound. Guess which develops an anion, which forms a cation, and the charges of each ion. Create the symbol because that each ion and also name them.

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

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

Check your LearningAluminum and carbon react to kind an ionic compound. Guess which forms an anion, which forms a cation, and the dues of every ion. Write the symbol for each ion and also name them.


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

The ions that us have questioned so much are dubbed monatomic ions, that is, they are ions developed from just one atom. We additionally find plenty of polyatomic ions. These ions, i m sorry act as discrete units, are electrically fee molecules (a group of bonded atoms with an as whole charge). Several of the much more important polyatomic ions are noted in Table 6. Oxyanions are polyatomic ions that contain one or much more oxygen atoms. At this point in your research of chemistry, you have to memorize the names, formulas, and also charges that the most usual polyatomic ions. Due to the fact that you will usage them repeatedly, they will certainly soon end up being familiar.

NameFormulaRelated AcidFormula
ammonium extNH_4^;;+
hydronium extH_3 extO^+
oxide extO_2^;;-
peroxide extO_2^;;2-
hydroxide extOH^-
acetate extCH_3 extCOO^-acetic acid extCH_3 extCOOH
cyanide extCN^-hydrocyanic acid extHCN
azide extN_3^;;-hydrazoic acid extHN_3
carbonate extCO_3^;;2-carbonic acid extH_2 extCO_3
bicarbonate extHCO_3^;;-
nitrate extNO_3^;;-nitric acid extHNO_3
nitrite extNO_2^;;-nitrous acid extHNO_2
sulfate extSO_4^;;2-sulfiric acid extH_2 extSO_4
hydrogen sulfate extHSO_4^;;-
sulfite extSO_3^;;2-sulfurous acid extH_2 extSO_3
hydrogen sulfite extHSO_3^;;-
phosphate extPO_4^;;3-phosphoric acid extH_3 extPO_4
hydrogen phosphate extHPO_4^;;2-
dihydrogen phosphate extH_2 extPO_4^;;-
perchlorate extClO_4^;;-perchloric acid extHClO_4
chlorate extClO_3^;;-chloric acid extHClO_3
chlorite extClO_2^;;-chlorous acid extHClO_2
hypochlorite extClO^-hypochlorous acid extHClO
chromate extCrO_4^;;2-chromic acid extH_2 extCr_2 extO_4
dichromate extCr_2 extO_7^;;2-dichromic acid extH_2 extCr_2 extO_7
permanganate extMnO_4^;;-permanganic acid extHMnO_4
Table 6. typical Polyatomic Ions

Note that there is a system for naming some polyatomic ions; -ate and -ite space suffixes designating polyatomic ion containing much more or under oxygen atoms. Per- (short for “hyper”) and also hypo- (meaning “under”) are prefixes definition more oxygen atoms 보다 -ate and also fewer oxygen atoms 보다 -ite, respectively. Because that example, perchlorate is ClO4−, chlorate is ClO3−, chlorite is ClO2− and also hypochlorite is ClO−. Unfortunately, the variety of oxygen atoms corresponding to a given suffix or prefix is not consistent; for example, nitrate is NO3− while sulfate is SO42−. This will be extended in an ext detail in the next module top top nomenclature.

The nature of the attractive pressures that organize atoms or ions together within a link is the basis for classifying chemistry bonding. As soon as electrons are transferred and ions form, ionic bonds result. Ionic bonds space electrostatic forces of attraction, the is, the attractive pressures experienced in between objects that opposite electrical charge (in this case, cations and also anions). As soon as electrons space “shared” and also molecules form, covalent bonds result. Covalent bonds room the attractive forces in between the positively charged nuclei of the external inspection atoms and also one or an ext pairs of electrons that room located in between the atoms. Compounds are classified together ionic or molecule (covalent) ~ above the basis of the bonds present in them.

Ionic Compounds

When an facet composed that atoms the readily lose electrons (a metal) reacts through an element composed the atoms the readily gain electrons (a nonmetal), a move of electrons typically occurs, creating ions. The compound developed by this transport is stabilized through the electrostatic attractions (ionic bonds) between the ions of the contrary charge present in the compound. Because that example, as soon as each salt atom in a sample that sodium metal (group 1) offers up one electron to kind a sodium cation, Na+, and also each chlorine atom in a sample of chlorine gas (group 17) accepts one electron to kind a chloride anion, Cl−, the resulting compound, NaCl, is created of sodium ions and chloride ions in the proportion of one Na+ ion because that each Cl− ion. Similarly, each calcium atom (group 2) can provide up 2 electrons and transfer one to every of two chlorine atoms to type CaCl2, i beg your pardon is created of Ca2+ and Cl− ions in the proportion of one Ca2+ ion to 2 Cl− ions.

A compound that has ions and is held together by ionic bonds is referred to as an ionic compound. The routine table can aid us recognize plenty of of the compound that space ionic: once a metal is an unified with one or more nonmetals, the compound is normally ionic. This guideline works well because that predicting ionic compound formation for many of the compounds typically encountered in an introduce chemistry course. However, it is not constantly true (for example, aluminum chloride, AlCl3, is no ionic).

You can regularly recognize ionic compounds since of your properties. Ionic compounds space solids that commonly melt at high temperatures and also boil at even greater temperatures. Because that example, salt chloride melts in ~ 801 °C and boils at 1413 °C. (As a comparison, the molecular link water melts in ~ 0 °C and boils at 100 °C.) In solid form, one ionic link is not electrically conductive since its ions are unable to circulation (“electricity” is the flow of fee particles). Once molten, however, it can conduct electricity because its ions are able come move freely through the liquid (Figure 3).

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Figure 3. sodium chloride melts at 801 °C and also conducts electrical power when molten. (credit: change of work-related by mark Blaser and also Matt Evans)