Table salt, ionic bonds

The electronegativity of sodium and chlorine differ by 2.23, whereas the difference between hydrogen and oxygen is only 1.24 (see Table 7.1). As a general rule, molecules made up of two atoms with electronegativity differences greater than 2.0 form ionic bonds. Molecules whose atoms have electronegativity differences of less than 2.0 form covalent bonds. Ionic-bonded salt and covalent-bonded water conform to that rule. 

Chlorine gas is very reactive, and causes horrific bums to the eyes and throat see p. 243. The two atoms are held together by means of a single, non-polar covalent bond. CI2 has a yellow-green colour and, for a gas, is relatively dense at s.t.p. Conversely, table salt (sodium chloride) is an ionic solid comprising Na+ and Cl- ions, held together in a three-dimensional array. What is the reason for their differences in behaviour ... 

The stability of such HCP is not high. For instance, although the heparin (ionic bonds) — ternary ammonium salts (covalent bonds) — polypropylene associate is not actually affected by distilled water, the 3 hours storage of the product in blood plasma reduces the surface concentration of heparin to 30% of its initial value65. It is noteworthy that heparin is very effectively eluted by solutions of y-globuline (Table 7)65>. 

A common example of an ionic solid is table salt (NaCl). Table salt is created when one atom of sodium (Na) creates an ionic bond with one atom of chlorine (Cl). Sodium loses its one outer electron (becoming a cation, Na+) while chlorine takes this electron (becoming an anion, Cl-). The Na+ cation bonds with the Cl- anion to form NaCl, common table salt. 

In Fig. 3, a solid line ties covalent bond and ionic bond to another. This is to show that both the covalently bonded and the ionic bonded electrons are both bosons. And quantum-mechanically they are equivalent to one another. At two extremity, i.e., 100% of covalent bond can be represented by a material known as diamond, whereas 100% of ionic bond can be represented by a material known as table-salt, Na(+)C1(-). All the organic and inorganic material in this universe can be assigned between these two extremities. The difference, from one material to another, lies only in terms of the percentage of covalency or ionicity. 

Ionic crystals consist of repeating patterns of oppositely charged ions, as shown in Figure 8.9. What happens when an ionic compound comes in contact with water The negative end of the dipole on some water molecules attracts the cations on the surface of the ionic crystal. At the same time, the positive end of the water dipole attracts the anions. These attractions are known as ion-dipole attractions attractive forces between an ion and a polar molecule. If ion-dipole attractions can replace the ionic bonds between the cations and anions in an ionic compound, the compound will dissolve. Generally an ionic compound will dissolve in a polar solvent. For example, table salt (sodium chloride, NaCl) is an ionic compound. It dissolves well in water, which is a polar solvent. 

Some of the halides of the alkaline earth metals have a similar identity problem. Calcium chloride and magnesium chloride have melting points almost as high as that of sodium chloride. Those compounds are clearly held together by ionic bonds. Beryllium chloride, on the other hand, melts at about half the temperature of table salt. And it boils at 520°C compared to salt s 1,465°C. The differences in properties are due to the partially covalent bond formed between beryllium and chlorine. 

One feature of metals is well known. Metals tend to lose electrons to nonmetals in a chemical reaction. That is, they tend to have lower electronegativities than nonmetals. This is obvious in compounds formed from metals at the far left of the periodic table and nonmetals from the far right. Sodium (a metal) clearly loses an electron to chlorine (a nonmetal) forming an ionic bond. The resulting compound—table salt—is a water-soluble, white... 

But the nature of the compounds formed when the metal and nonmetal are closer to the center of the periodic table is less obvious. Their electronegativities are closer together. And the electronegativity difference between the atoms in a compound determines the nature of the bond. Recall that differences of 1.7 or more result in ionic bonds atoms with differences less than 1.7 form bonds with some covalent character. Lead sulfide (PbS) is an example of such a compound. Lead has an electronegativity of 1.9 sulfur is 2.5. The difference of 0.6 is less than 1.7, so the bond between them should have some covalent character. Like sodium chloride, lead sulfide is a crystalline compound. However, it is dark and shiny, quite unlike salt. It is also insoluble in water, which indicates a high degree of covalency in the lead-sulfur bond, just as one would expect. 

Some crystals are ionic, that is, long networks of ions held together by ionic attractions. Sodium chloride, table salt, is an ionic solid. In crystals of sodium chloride, a sodium ion is surrounded by six chlorine ions— one on top, one on the bottom, and one at each compass point—and each chloride ion is surrounded by six sodium ions in the same manner. Crystals of sugar, on the other hand, are held together by intermolecular attractions. They fit together for optimum balance of attraction and repulsion so that a quite orderly crystalline structure results. Pure metals are stacks of identical atoms so the bonding between one pair cannot be any different than the bonding between the next pair. Consequently, it is impossible to... 

The force of attraction between the l-i- charge on the sodium cation and the 1- charge on the chloride anion creates the ionic bond in sodium chloride. Recall that sodium chloride is the scientific name for table salt. Chemists call table salt by its scientific name because the word salt can actually be used to describe any one of thousands of different ionic compounds. Other salts that are commonly found in a laboratory include potassium chloride, magnesium oxide, and calcium iodide. 

Recall that the smallest crystal of table salt that you could see contains many billions of sodium and chloride ions all held together by ionic bonds. However, if you could look closely enough into the salt, all you would see are many Na" and Cl ions all bonded together to form a crystal. There are no NaCl molecules. 

You ve probably noticed how similar table salt, an ionic solid, and table sugar, a covalent solid, are in appearance. But if you heat salt on the stove, it won t melt, even if the temperature is high. Sugar, on the other hand, melts at a relatively low temperature. Does type of bonding affect properties ... 

Bond Formation The positive sodium ion and the negative chloride ion are strongly attracted to each other. This attraction, which holds the ions close together, is a type of chemical bond called an ionic bond. In Figure 13, sodium and chloride ions form an ionic bond. The compound sodium chloride, or table salt, is formed. A compound is a pure substance containing two or more elements that are chemically bonded. 

Perhaps the most common example of an ionically bonded substance is NaCl, or table salt. In this, the sodium (Na) atom gives up an electron to the much more electronegative chlorine (Cl) atom, and the two atoms become ions, Na and Cl. The electrostatic bonding force between the two oppositely charged ions extends outside the local area attracting other ions to form giant crystal structures. For this reason most ionically bonded materials are solid at room temperature. 

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