Covalent Bonding and Molecular Compounds

6.2 Covalent Bonding and Molecular Compounds

​Most chemicals that exist in living things are composed of molecules.

Multiple Choice

Carbon is very useful as the "building block" of larger molecules because

• It can bond with up to four other atoms at one time.

• It is highly reactive with water.

• It is very stable.

• One atom of carbon can make numerous double and triple bonds.

Many chemical compounds consist of MOLECULES.

• A neutral group of atoms that are held together by covalent bonds.

• A single molecule of a compound is capable of existing on its own.

Multiple Choice

What main characteristic separates molecules from other types of compounds?

• molecules are held together by transferring electrons

• molecules are held together by sharing electrons

• molecules are highly unstable

• molecules can't exist as individual units

Compounds are made of two or more atoms of different elements.

• Atoms can be bonded ionically (charge) or covalently (by sharing electrons)

• ​"All compounds are molecules but not all molecules are compounds"

All compounds have a chemical formula.

• Indicates the relative numbers of atoms of each kind in a compound.

Covalent compounds have a MOLECULAR FORMULA.

• Shows the types and numbers of atoms in a single molecule of a molecular compound (a covalent substance).

• "Molecular Compound" = "Covalent Compound"

Multiple Choice

According to the molecular formula for glucose, C₆H₁₂O₆, how many hydrogens are present in one molecule of glucose?

• 3

• 6

• 12

• none

​Summing it Up...

• ​Only covalently bonded atoms form "MOLECULES"

• ​All compounds are molecules but not all molecules are compounds.

• ​Compounds can be covalent OR ionic (we'll talk about ionic compounds next).

• ​All compounds have a chemical formula, but ONLY COVALENT COMPOUNDS have a MOLECULAR FORMULA.

Multiple Choice

True for False: "All covalent compounds are molecules, but not all covalent molecules are compounds"

• True

• False

Covalent bonds form from shared electrons.

• Atoms have lower potential energy when bonded (more stability

Multiple Choice

If two atoms have a "triple bond", how many PAIRS of electrons are being shared?

• 1 pair

• 2 pairs

• 3 pairs

• 4 pairs

Multiple Choice

If two atoms have a double bond, how many ACTUAL electrons are being shared?

• 2

• 3

• 4

• 5

Bond lengths and energy vary from molecule to molecule.

• Bond length is the average distance between two bonded atoms.

• Bond energy is the amt. of energy required to break a chemical bond.

Multiple Choice

The relationship between bond length and bond energy is...

• inversely proportional; as one increases the other decreases

• directly proportional; as one increases the other increases

Atoms tend to form bonds to follow the octet rule.

• A "full outer shell" means more stability/lower potential energy.

• H and He are exceptions to the octet rule.

Multiple Choice

Why are Hydrogen and Helium exceptions to the octet rule?

• They already have 8 valence electrons

• They already have a full outer shell

• They only have one orbital

• They are the boss

Valence electrons are involved in bonding.

• The group number can tell you how many valence electrons an atom has.

• Groups 1 and 2 have "1" and "2" e^- respectively.

• Group 13 has "3",, group 14 has "4", and so on through group 18...

Multiple Choice

Which electrons are involved in covalent bonds?

• inner electrons

• all electrons

• valence electrons

• reactive electrons

Transition metals vary in their number of valence electrons.

• Transition metals can "move" their valence electrons around, so we need to consider what they're bonding with.

• You'll be able to figure this out later...

Other exceptions to the octet rule...

• Boron typically achieves 6 valence e^-, and beryllium with 4.

• Highly electronegative atoms, like fluorine, oxygen, and chlorine, can have more than 8 valence e-

Dots are used to represent valence electrons in an electron-dot notation.

• Each dot represents an electron.

• A total of 4 PAIRS of electrons shows an octet

Multiple Choice

The single dots in a Lewis dot diagram represent

• shared electrons

• electron pairs

• potential bonding sites

• absolutely nothing meaningful

Lewis structures show atoms as they are bonded to each other.

• Dots are unpaired electrons

• Dashes are a shared pair of electrons

• Single bonds = 1 line = 1 PAIR of electrons

• Multiple bonds = more than 1 line

Multiple Choice

A Lewis structure with a total of three lines is sharing how many pairs of electrons?

• 1

• 2

• 3

• 6

Multiple Choice

Which electrons do you consider when building a Lewis structure?

• all of them

• only the valence electrons

• the inner electrons

• none of them

Resonance Structures

• "mirror" images of a molecule; when one diagram can't suffice.

• shown by a double-headed arrow between the structures.

A structural formula indicates the number, arrangement and bonds, but not the unshared pairs of electrons.

• more simple