Chapter 8 - Chemistry

Intermolecular force

A force of attraction that occurs between molecules

Partial Charges

A less than full charge on part of a molecule, created by the unequal sharing of electrons. Partial charges are represented with the symbol delta (8+ for partial positive charge and 8- for partial negative charge.)

Electronegativity

A measure of the ability of an atom in a molecular substance to attract electrons to itself that are involved in a bond.

Use electronegativity to explain why some molecules are attracted to a charged wand.

Because of the difference in electronegativity of atoms in a molecule, some molecules have dipoles in which the electrons are attracted more to one end of the bond than the other. The molecule then acts like a miniature magnet, and the positive end of the molecule is attracted to a negatively charged wand.

What are nonpolar molecules with two identical atoms?

Diatomic molecules

Explain how electronegativity values help you to determine the polarity of a bond between two atoms.

Electronegativity values help determine the polarity of the bond between two atoms because they can be used to determine the tendency of an electron to be attracted to one atom rather than another atom.

What does polarity have to do with the smell of small molecules?

Polar molecules have properties that distinguish them from nonpolar molecules. Polar molecules dissolve in water and are attracted to other polar molecules

What does polarity have to do with smell?

Polar molecules have properties that distinguish them from nonpolar molecules. Polar molecules dissolve in water and are attracted to other polar molecules. Polar substances dissolve in the mucous membrane of the nose, whereas nonpolar substances are simply exhaled undissolved and undetected.

Why do some molecules smell while others do not?

Polarity is responsible for intermolecular attractions that affect many properties of molecules, including smell properties. Polar Molecules are attracted to a charged wand because they have partial charges distributed within the molecule. Non polar molecules are not attracted to a charged wand.

Smelling substances

Substances that are most likely to have a smell are molecular covalent compounds that form small to medium-sized polar molecules. Small and medium-sized molecules are most likely to travel to the nose because they are more likely to become gases. Polar compounds are more likely to have a smell because they interact better with receptor sites in the nose.

What generalizations can you make about smell and molecules?

The first requirement for a substance to be smelled is that it be in a gaseous form. The size of the molecule seems to be another important factor in predicting smell. Most medium-sized molecules will smell. Most large-sized molecules will not smell.

How can electronegativity be used to compare bonds?

The greater the electronegativity difference, the more polar the bond. The electrons in a polar bond tend to spend more time around the more electronegative atom. When the difference between the electronegativities of two bonded atoms is greater than about 2.1, the bond is considered ionic and one atom gives up an electron to the other atom, forming two ions.

How does electronegativity relate to the tendency to form negative ions?

The most electronegative atoms tend to attract electrons from other atoms, thereby making the atom partially negative.

If the bonds between atoms of a molecule are polar, what about the molecule as a whole unit?

To figure out which end of a molecule has a partial negative charge and which end has a partial positive charge, check the electronegativities of the atoms and the overall shape of the molecule.

What makes a nonpolar covalent bond?

When atoms with identical electronegativities bond together and the electrons are shared equally.

What makes a polar covalent bond?

When two different kinds of atoms bond together, they do not attract the bonding electrons equally. The electrons are attracted to the atom with greater electronegativity. The result is a polar covalent bond.

Do small molecules that are polar have smell?

Yes. And small molecules that are non-polar do not have smell.

Is hydrogen always partially positive when bonded to another atom?

No, hydrogen will have only a partial positive charge when it is bonded to an atom that has a greater electronegativity.

diatomic molecules

A molecule consisting of two atoms

Dipole

A molecule or covalent bond with a non-symmetrical distribution of electrical charge that makes the molecule or bond polar.

Polar Molecules

A molecule that has a negatively charged end and a positively charged end due to to electronegativity differences between the atoms and/or the asymmetry of its structure.

Non polar molecules

A molecule that is not attracted to an electrical charge. A molecule is nonpolar if each atom shares electrons equally or there is no net dipole in the molecule.

Why is carbon dioxide a nonpolar molecule even though its bonds are polar?

Although the two carbon-oxygen bonds of carbon dioxide are polar, the molecule itself has a linear shape, so the partial negative charges are on opposite sides of the molecule. These charges balance one another, so there is no net dipole.

What makes an electron transfer and an ionic bond?

If two atoms involved in a bond differ greatly in electronegativity.

What is the difference between a polar covalent bond and a nonpolar covalent bond?

In a polar covalent bond, the electron is attracted more by one atom than by the other, so one of the atoms has a partial negative charge and the other has a partial positive charge. In a nonpolar covalent bond, in which the two atoms share the electrons equally, there are no partial charges.