Covalent Bonding

Remember… Atoms want to be stable so they will obey the octet rule. The octet rule states that atoms gain, lose, and share valence electrons to achieve an outer octet of 8 valence electrons. When forming ionic compounds, metals transfer valence electrons to nonmetals until all atoms obey the octet rule.

Atoms in covalent compounds share valence electrons until all atoms obey the octet rule. Atoms involved in covalent bonding are nonmetals and some metalloids. Def: Covalent bond forms when atoms share valence electrons. Def: A molecule forms when 2 or more atoms are covalently bonded.

Lewis Symbols

Bonding Electrons that are paired will not share to form bonds. Single, unpaired electrons will share to form covalent bonds. What kinds of bonds can these atoms make?

Bonding So, if carbon can make 4 bonds, let’s combine it with F. Since carbon can make two sets of two bonds, lets combine it with oxygen.

Let’s look at some of the molecules you made. These are called Lewis dot structures or dot structures.

Definitions Def. Single covalent bond forms when 2 atoms share 2 electrons. Def. Double covalent bond forms when 2 atoms share 4 electrons. Def. Triple covalent bond forms when 2 atoms share 6 electrons.

Some atoms bond with themselves to form diatomic molecules. Formula Name H2 Hydrogen Cl2 Chlorine N2 Nitrogen Br2 Bromine O2 Oxygen I2 Iodine F2 Fluorine

Lewis Structures for Diatomic Molecules

Lengths & Strengths of Covalent Bonds Single bond C C Double bond C C Triple bond C C  

Bonds and Energy When bonds form or break, energy is involved. When bonds form, the molecule that forms is more stable than the atoms it is made of. That means that, when the bond forms, energy is released. When energy is released, it is called an exothermic reaction

Bonds and Energy When bonds break, energy is required to break the bond. That means that energy must be absorbed for the bond to break. This is an endothermic reaction when energy is absorbed.

Naming Binary Covalent/Molecular Compounds. Covalent compounds are also called molecular compounds. They are named using prefixes to indicate how many of each element is included.

Prefixes *Only mono- is NOT used with the name of the first element in the compound. Number of Atoms Prefix 1 mono- 5 penta- 8 octa- 2 di- 6 hexa- 9 nona- 3 tri- 7 hepta- 10 deca- 4 tetra-  

Practice Naming Covalent Compounds SO3 P4O10 B2F6 N2O5

Formula Writing of Covalent Compounds Carbon tetrachloride Diphosphorus trioxide Dinitrogen monoxide Chlorine trifluoride

Acids Acids are compounds that, when dissolved in water, produce hydrogen ion (H+). There are two common types of acids – binary and oxyacids/oxoacids.

Binary Acids Binary acids contain hydrogen and 1 type of nonmetal and follow this naming rule: Hydro _______ ic acid Formula Name HF Hydrofluoric acid HCl Hydrochloric acid HBr Hydrobromic acid HI Hydroiodic acid H2S Hydrosulfuric acid

Oxyacids Oxyacids contain hydrogen and a polyatomic acid The naming rule is: if the polyatomic ion ends in –ate, the acid name ends in –ic. If the polyatomic ion ends in –ite, the acid name ends in –ous. Add one hydrogen to the front of the acid for each NEGATIVE charge.

Polyatomic ion formula Oxyacids Polyatomic ion formula Polyatomic ion name Oxyacid Name Oxyacid formula NO3- Nitrate Nitric acid HNO3 SO42- H2CO3 BrO2- Acetate Phosphorous acid

Ways to Represent Covalent Compounds

Definitions Def: Bonding pairs of electrons are electrons shared between atoms. Def: Lone pairs of electrons are electrons located on an atoms and not shared with another atom. Def: Resonance structures are different dot structures needed to correctly represent a molecule. Def: Formal charge is the charge assigned to an atom in a molecule based on arrangement of valence electrons.

Creating Dot Structures The Steps. Count the total number of valence electrons available for bonding. 2. Arrange the atoms with one central atom. This will be the one with the lowest electronegativity. 3. Place a pair of electrons (bond) between each pair of atoms. 4. Use remaining electrons to complete octets on atoms. 5. Any electrons left are lone pairs. Pace them where needed to complete octets.