MCAT Physical : Ionic Bonds

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #1 : Ionic Bonds

What type of bond is formed in potassium iodide?

Possible Answers:

Polar covalent bond

Polar ionic bond

Ionic bond

Nonpolar covalent bond

Correct answer:

Ionic bond

Explanation:

Potassium iodide (KI) forms an ionic bond. Potassium and iodine have very different electronegativities. The two atoms would form an ionic bond since ionic bonds form between atoms with a large difference in electronegativity (difference>1.7 using the Pauling scale will result in an ionic bond). 

Example Question #2 : Ionic Bonds

Which of the following compounds contain an ionic bond?

Possible Answers:

Correct answer:

Explanation:

Ionic bonds are bonds in which there is a complete transfer of electrons between two elements. They are formed between two elements with a large difference in electronegativity, like a metal and nonmetal. Molecules with similar electronegativities share their electrons and form covalent bonds.

Because bromine has a much higher electronegativity than potassium, it will fully take an electron from potassium to form a complete octet, leaving potassium also with a complete octet.

, , and all form covalent bonds and share electrons between the atoms of the molecule.

Example Question #3 : Ionic Bonds

The electronegativities of certain elements are given below:

Which of the following compounds is most ionic in character?

Possible Answers:

Correct answer:

Explanation:

The degree of ionic character of a compound is determined by comparing the electronegativities of the species involved. The greater the difference in electronegativity, the more ionic the compound.

Here the greatest arithmetic difference is found in yttrium trichloride.

Example Question #4 : Ionic Bonds

Which of the following is the correct name for the compound  ?

Possible Answers:

Potassium oxide

Potassium monoxide

Potassium (II) oxide

Potassium (I) oxide

Dipotassium monoxide

Correct answer:

Potassium oxide

Explanation:

The compound  contains a metal (potassium) and a nonmetal (oxygen), so it is an ionic compound, with no transition metals. To name an ionic compound, the following rules apply:

- the metal component's name does not change, regardless of quanitiy or charge

- the non-metal component's name ends in -ide, and has no prefix 

- if the metal is a transition metal, the metal's charge is specified with a Roman numeral

Using these rules, the correct name is potassium oxide.

Example Question #5 : Ionic Bonds

Which of the following most accurately describes an ionic bond?  

Possible Answers:

An attractive force exists between a cation, which has gained electrons, and an anion, which has lost electrons.

An attractive force exists between two atoms that have one or more of the same electrons in valence shells.

An attractive force exists between a cation, which has lost electrons, and an anion, which has gained electrons.

Positive and negative poles form on a molecule that is made of two nonmetals with different electronegativities.

Correct answer:

An attractive force exists between a cation, which has lost electrons, and an anion, which has gained electrons.

Explanation:

An ionic bond is an electrostatic force between a positively charged cation (formed when electrons are lost) and a negatively charged anion (formed when electrons are gained). While one answer choice mentions positive and negative, it is actually a description of a polar covalent bond. The easiest way to recognize this is the fact that it specifies a bond between two nonmetals. A metal in generally a component of an ionic compound.

Example Question #6 : Ionic Bonds

Which of the statements are true about ionic compounds?

Possible Answers:

They are formed by molecules that equally share electrons

They are non-polar

Water is an example of an ionic compound

They are 3D arrays of charged molecules

Correct answer:

They are 3D arrays of charged molecules

Explanation:

Ionic compounds are made of atoms that are held together by ionic bonds. These bonds allow charged particles that have very different electronegativities to stick together, forming 3D crystals. For example, potassium and bromine form potassium bromide, an anti-convulsant. The electrons are shared very disproportionately between the positive and negatively charged particles, with the all the electrons located on the more electronegative atom. Ionic compounds are not non-polar because non-polar is used to describe a molecule whereas ionic compounds are not molecules. Water is an example of a polar molecule but is not an ionic compound since The hydrogens and oxygen share their electrons.

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