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Which of the following pairs of elements is most likely to form an ionic compound?

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Which of the following pairs of elements is most likely to form an ionic compound?

Give it up Brooke. And by the way, there are no 100% ionic compounds.

This is a tricky concept because there is not a clear distinction between ionic and covalent bonds and between ionic and covalent compounds. “Ionic” and “covalent” exist on a continuum. Most bonds have characteristics of both ionic and covalent bonds.

In fact there are NO 100 percent ionic compounds. Even the bonds in CsF which have the greatest electronegativity difference (DEN) are 8 percent covalent.

More chemical bonds are covalent than are ionic. All bonds like along a continuum between ionic and covalent and have some characteristics of both. We choose an arbitrary point (where the electronegativity difference is above 2.0) to say that a bond is predominately ionic.

It is possible to compute the percent ionic character in a bond with the following formula:

percent ionic character = 100(1 – e^(-DEN^2/4) )

There are many folks who still don’t understand that bonding cannot be reduced to either “ionic” or “covalent. Keep in mind that there are NO compounds which are completely ionic. Actual chemical bonds lie along a continuum between covalent and ionic. Even the most ionic of bonds (Cs-F) is not completely ionic (it is 8 percent covalent) and share electrons to a certain degree.

Therefore, it really doesn’t make sense to try to peg a bond as either “ionic” or “covalent”. What does make sense is to try to place the bond somewhere along the continuum. The key is to look at the electronegativity differences. The greater the electronegativity difference, the greater the percent ionic character.

For instance, in benzoic acid there are C-O bonds which are quite covalent and O-H bonds which are also very covalent, as well as C-H bonds which are almost 100 percent covalent.

In KCl the bonds are very polar covalent. The electronegativity difference is (3.16-0.82 = 2.34) great enough to say that the bonds behave as if they were ionic (yet the percent ionic character is 75 percent ionic, or 25 percent covalent).

Sodium sulfate also has a high percent ionic character, while sucrose has bonds which are much more covalent in nature (it has the same bonds as does benzoic acid).

Sometimes people think that if they dissolve the compound in water and the solution conducts electricity that the compound will be ionic. This only works part of the time. Lots of molecular compounds with covalent bonds will dissolve in water to produce ions which will make the solution conduct electricity. So this turns out to be an ineffective test for ionic vs covalent compounds. The best example of why this doesn’t work in hydrochloric acid. Hydrochloric acid is produced with molecular HCl gas, with covalent bonds, dissolves in water to produce hydrogen ions and chloride ions. There are many other compounds which will produce ions in solution, but which have predominately covalent bonds.

A better test that involves conductivity is to melt the compound. If the molten substance conducts electricity then there is a greater likelihood that the compound contains ions, and has ionic bonds.

In fact, the oxidation state of an element will determine how ionic or covalent the bonds are. Consider permanganate ion, MnO4-. In permanganate the bonds are much more covalent than the bonds between Mn and Cl in MnCl2 even though oxygen is more electronegative than chlorine.

Sometimes people will try to use melting point as an indicator of ionic or covalent bonds. The melting point is determined by intermolecular forces, not the type of bonding within the molecule. In fact the substance with the highest melting point, diamond, is composed of purely covalent bonds.

The bottom line is that the type of bonding is not as clear cut as some teachers (who aren’t chemists) try to make it out to be. To determine the predominate type of bonding you really need to look at a variety of factors including dipole moment, bond energy, electronegativity difference, and whether the compound forms discrete molecules or exists as a network solid.

2. Which pair of elements will likely form an ionic bond?

2. Which pair of elements will likely form an ionic bond? – Which of the following chemical formulas correctly represents 2 molecules of silver bromide? 2AgBr C. Ag2Br2 Ag(Br)2 D. 2Ag2Br2 6. What is the What is the correct formula for the compound lithium oxide? 9. The compound formed from the elements calcium and chlorine is known as Chlorine…Which of the following pairs of elements and valence electrons is incorrect? Which of the following does not have a noble gas electron configuration? (or Which of the following is not (c) four single bonds around the central carbon atom. (d) two equivalent resonance forms.11) Which of the following compounds would you expect to be ionic? The charge of 13) Which pair of elements is most likely to form an ionic the ion is -1. compound with each other?

Sample Questions – Chapter 7 – Which are likely to be molecular? (a) SiCl4 — Molecular(b) LiF– Ionic(c) BaCl2– Ionic(d) B2H6 — Molecular(e) KCl– Ionic(f) C2H4– Molecular(Reference: Chang 2.49) 9.What is the l.CuSO4⋅ 5H2O – Copper (II) Sulphate Monohydrate 11. Write the formulas for the following compounds: (18 points) 12.1.Ionic Compounds Often Have High Melting and Boiling Points The attraction between cations and anions is often very strong and hard to break. Mg+2 O-2 c. lithium oxide Li+1 Li2O O-2 d. calcium fluoride -1 +2 F Ca CaF2 # 20 Which pairs of elements are likely to form ionic compounds? a. ClThe three ions would adhere (bond) to each other by the positive/negative attraction between the ions. Ionic bonds occur between metals and non-metals on the periodic table. Turn to your periodic table and examine the three columns headed by Li (ignore hydrogen, if it is there), Be, and B…

Sample Questions - Chapter 7

ANSWERS_ionic-bonding-and-ionic-compounds… – Which of the following pairs of elements are likely to form ionic compounds? Check all that apply. sodium and potassium nitrogen and iodine potassium and sulfur chlorine and bromine helium and oxygen anocium and chlorine.When searching for pairs of elements that will form an ionic bond, one must be a metal and one must be a nonmetal. Importantly, noble gases, although nonmetals, do not form ionic bonds.Arrange the following compounds in order of increasing solubility in water: * O2 * LiCl * Br2 * CH3OH Like dissolves like; that is, polar compounds usually are soluble in water A.Li and S B.O and S C.Al and O d.F and Cl e.I and K F.H and N Which of the following pairs of elements will not form ionic.

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