AP Chemistry : Compounds and Molecules

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #1 :Types Of Chemical Bonds

What type of bond is present between the atoms of carbon dioxide?

Possible Answers:

Nonpolar covalent

Polar covalent

Ionic

Coordinate covalent

Correct answer:

Polar covalent

Explanation:

二氧化碳碳水化合物之间的双键n and oxygen molecules. Since there is a moderately large electronegativitiy difference between C and O, the bond can be described as polar covalent.

Though the bonds themselves are polar, the overall symmetry of the molecule means that carbon dioxide has a net zero dipole and is a nonpolar compound.

Example Question #81 :Compounds And Molecules

Which of the following describe a covalent bond?

Possible Answers:

Electrons are being shared

The metal accepts an electron

The nonmetal gives up an electron

None of these

Both metals give up an electron

Correct answer:

Electrons are being shared

Explanation:

In a covalent bond, electrons are shared between two nonmetals. If there is a metal in the compound, that is called an ionic compound, not a covalent compound. Ionic bonds involve the complete transfer of an electron from one species to another.

Example Question #1 :Types Of Chemical Bonds

What type(s) of bond(s) is/are present in the following molecule?

RbCl

Possible Answers:

complex ionic

ionic

covalent

network ionic

network covalent

Correct answer:

ionic

Explanation:

An ionic bond is a bond between a metal (Rb) and a nonmetal(Cl)

Example Question #1 :Types Of Chemical Bonds

What type of compound is?

Possible Answers:

Metallic

Ionic

Covalent

Polyatomic ion

Correct answer:

Ionic

Explanation:

Ionic compounds are formed between metals, which want to loose electrons, and nonmetals, which want to gain electrons. The sodium (Na) will completely transfer an electron to the chlorine (Cl), giving both atoms a complete octet without sharing electrons.

Covalent compounds generally form between two nonmetals that will both share electrons to complete their octets. Metallic compounds are built from only metals. Polyatomic ions will have a formal charge.

Example Question #1 :Ionic Bonding

Which of the following compounds is not held together by ionic bonds?

Possible Answers:

Correct answer:

Explanation:

Covalent bonds are formed when two nonmetals are bonded together. This covalent bond means that the electrons are shared by the two atoms in order to satisfy each atom's octet. There is very little difference in the electronegativities of the two atoms involved in the bond, so neither atom pulls the electrons closer to its nucleus.

Ionic bonds are formed between a metal and a nonmetal. Due to the dramatic difference between the electronegativities of metals and nonmetals, the electrons are pulled tightly to the nonmetal, and away from the metal nucleus. This results in each atom having a full octet, even though the electrons are not shared.

Carbon and oxygen are both nonmetals, so we would expect only covalent bonds in carbon dioxide.

Example Question #81 :Compounds And Molecules

Which of the following is not a characteristic of ionic compounds?

Possible Answers:

Comprised of atoms sharing electrons

High melting point

High boiling point

Good conductors of electricity in the aqueous state

Correct answer:

Comprised of atoms sharing electrons

Explanation:

Atoms share electrons in covalent bonds, not ionic. In ionic bonding, one or more electrons from an atom with a lower ionization energy are transferred to an atom with greater electron affinity.

Example Question #81 :Compounds And Molecules

Which of the following statements best describes ionic compounds?

Possible Answers:

3-D arrays of charged particles

Malleable compounds that lack structural stability

Formed when molecules share electrons

Neutral particles that donate electrons

Correct answer:

3-D arrays of charged particles

Explanation:

The definition of ionic compounds are three-dimensional arrays of atoms held together by strong ionic bonds. Ions are charged particles that have either gained or lost a certain number of electrons. They have great crystalline strength because of the strong electrostatic forces between the ions.

Example Question #1 :Intramolecular Force And Potential Energy

下面哪个选项包含(s)分子内hydrogen bonding?

I. NH3

II. HF

III. HCOH

IV. CH3CH2CH2OH

Possible Answers:

II and I

I, II, III, IV

II and IV

I only

I, II, IV

Correct answer:

I, II, IV

Explanation:

H bonding is when a H is bonded to either N, O, or F. In the third molecule, the O is only double-bonded to the C; it is not bonded to a single H. All other choices have a N, O, or F bonded to a H

Example Question #2 :Intramolecular Force And Potential Energy

Which of the following best explains hydrogen bonding?

Possible Answers:

The covalent bonds between other atoms are hydrogen are called hydrogen bonds

There are too many electrons in a solution, so H atoms interact with them

Electronegative atoms carry most of the electrons in the shared pairs when they are bonded to hydrogen

Hydrogen does not have any electrons

Correct answer:

Electronegative atoms carry most of the electrons in the shared pairs when they are bonded to hydrogen

Explanation:

Electronegative atoms disproportionately pull covalently bonded electrons toward themselves, which leaves hydrogen with partial positive character.

Example Question #1 :Intramolecular Force And Potential Energy

Hydrogen bonding can occur between which two molecules?

Possible Answers:

Methanol and water

Methane and water

Water and hydrogen gas

Hydrogen bonding can not occur between any of these combinations

Methanol and methane

Correct answer:

Methanol and water

Explanation:

为氢键发生必须有一个摩尔cule with a hydrogen bonded to either F,O,N. This is present in water and methanol which both have O-H bonds. There can be hydrogen bonding between two water molecules, and there can be hydrogen bonding between two methanol molecules. The key to this problem is recognizing that it is asking for a situation in which hydrogen bonding is occuring between two separate molecules.

Hydrogen bonding is the association of a hydrogen and one of the three most electronegative elements F,O,N of neighboring molecules. The hydrogen, because it is bonded to one of these elements, aquires a partially positive charge, F,O, or N develops a partially negative charge. The partially positive hydrogen will associate, not bond, with the F,O, or N of a seperate molecule. Remeber that hydrogen bonding is an intermolecular property, so it is occuring between separate molecules.

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