Chapter 2.2: Atoms Bond to Form Molecules

Flashcards from Chapter 2.2 of Principles of Life, 3rd Edition.

Chemical bond

An attraction between two atoms

Covalent bond

Strong bonds that result from the sharing of electrons

• Forms when two atoms attain more stable configurations by sharing one or more pairs of electrons

• Represented in structural formulas by lines drawn between the bonded atoms

• Electronegativities cannot be too dissimilar; most common biological molecules have similar electronegativities and form covalent bonds if needed

Orientation

Property of covalent bonds where the length of a covalent bond between a given two elements is the same, and where the angle of each covalent bond with respect to others is also the same

Bond strength

Depends on the atoms involved to determine if a reaction will form

Nonpolar covalent bond

A type of covalent bond that occurs when atoms are shared about equally with the “pull” of each nucleus on the electrons not having a large delta (under a 0.5 difference)

Polar covalent bond

A type of covalent bond where electrons are unequally shared between the two atoms, in a slight charge difference

• Seen in H₂O, with electrons pulled closer to oxygen due to greater electronegativity

Dipole

A separation of opposite electric charges, such as those in a polar covalent bond

Dipole-dipole interactions

Where a compound can be attracted to slightly oppositely charged atoms in other bonds, creating a weak bond

Ionic bond

Strong bonds that result from the transfer of atoms to another configuration

• Occurs between high and low electronegative atoms, creating oppositely-charged ions (greater than 2 difference)

• These tend to form crystal lattices with regular, recurring arrangement of the anions and cations (like in table salt)

• They also often dissolve in water, rendering the strength irrelevant

Ion

An atom that gains or loses one or more electrons

Cation

The positively charged ion that lost one or more electrons

Anion

The negatively charged ion that gained one or more electrons

Molecule

This is formed when two or more atoms join together chemically

Compound

A molecule formed by at least two different elements

Hydrogen bond

A weak bond caused by electrostatic attractions between slightly-positively charged H and slightly-negatively charged O or N atoms

• This is an example of a dipole-dipole interaction

• Many can form within one molecule or between molecules, adding strength and determining molecular shape in some cases

van der Waals interactions

Transient electrostatic attraction between two atoms, each of which is in a nonpolar covalent bond

• Very small dipoles may form here because of minute asymmetries in electron orbit, which can induce a temporary dipole if close enough