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Covalent Bonding

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Electrons that are shared by atoms are called bonding pairs.
Electrons that are not shared by atoms but belong to a particular atom are called lone pairs.
Also known as nonbonding pairs
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- The top and bottom electrons on the O atom are lone pairs

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When two atoms share one pair of electrons, the result is called a single covalent bond.
Two electrons
One atom may use more than one single bond to fulfill its octet.
To different atoms + H only duet

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When two atoms share two pairs of electrons, the result is called a double covalent bond.
Four electrons between the two atoms
- Example: O2
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Elements that can double-bond with each other and themselves are C, N, O, S, and P

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When two atoms share three pairs of electrons, the result is called a triple covalent bond.
Six electrons between the two atoms
- Example: N2
Elements that can triple-bond with each other and themselves are C, N, O, and S.

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Lewis theory
implies that some combinations should be stable, whereas others should not. + Stable combinations result in “octets.”
allows us to predict the formulas of molecules of covalently bonded substances. + Hydrogen and the halogens are all diatomic molecular elements, as predicted by Lewis theory. + Oxygen generally forms either two single bonds or a double bond in its molecular compounds.
- There are some stable compounds in which oxygen has one single bond and another in which it has a triple bond, but it still has an octet.

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Lewis theory of covalent bonding
implies that the attractions between atoms are directional. + The shared electrons are most stable between the bonding atoms.
predicts that covalently bonded compounds will be found as individual molecules. + Rather than an array like ionic compounds
- Compounds of nonmetals are made of individual molecule units.

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Molecular compounds are composed of two or more nonmetals.
The formula for a molecular compound cannot readily be determined from its constituent elements because the same combination of elements may form many different molecular compounds, each with a different formula.
Nitrogen and oxygen form all of the following unique molecular compounds:
- NO, NO2, N2O, N2O3, N2O4, and N2O5.

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Names of Molecular Compounds:
Write the name of the element with the smallest group number first.
If the two elements lie in the same group, then write the element with the greatest row number first.
The prefixes given to each element indicate the number of atoms present.

If there is only one atom of the first element in the formula, the prefix mono- is normally omitted

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Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule

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Molar mass in combination with Avogadro’s number can be used to determine the number of atoms in a given mass of the element.
Use molar mass to convert to the amount in moles. Then use Avogadro’s number to convert to number of molecules. +

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How many H atoms are in 72.5 g of C3H8O ?
Mass percent composition of an element in a compound =
- n is the number of moles of the element in 1 mole of the compound
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What is the mass percent of Ca in CaCl2
CaCl2 (Ca = 40.08, Cl = 35.45)

term	Definition
bonding pairs	Electrons that are shared by atoms
lone pairs (nonbonding pairs)	Electrons that are not shared by atoms but belong to a particular atom
single covalent bond	when two atoms share one pair of electrons
double covalent bond	when two atoms share two pairs of electrons
triple covalent bond	when two atoms share three pairs of electrons