Chapter 8 Covalent Bonding

Sharing is Caring The atoms held together by sharing electrons are joined by a Covalent Bond.

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

Molecules and Molecular Compounds Molecule is a neutral group of atoms joined together by covalent bonds. Diatomic molecule is a molecule consisting of two atoms. A compound composed of molecules is called a molecular compound.

Properties Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds. Many are gases or liquids at room temperature. Most are formed from atoms of two or more nonmetals.

Molecular Formulas A molecular formula is the chemical formula of a molecular compound. It shows how many atoms of each element a molecule contains. CO2 Carbon Dioxide 1 Carbon Atom 2 Oxygen Atoms

Ionic Vs. Covalent Bond

So what are covalent bonds?

In covalent bonding, atoms still want to achieve a noble gas configuration (the octet rule).

But rather than losing or gaining electrons, In covalent bonding, atoms still want to achieve a noble gas configuration (the octet rule). But rather than losing or gaining electrons, atoms now share an electron pair.

The shared electron pair is called a bonding pair In covalent bonding, atoms still want to achieve a noble gas configuration (the octet rule). But rather than losing or gaining electrons, atoms now share an electron pair. The shared electron pair is called a bonding pair

Chlorine forms a covalent bond with itself Cl2

How will two chlorine atoms react? Cl Cl

Cl Cl Each chlorine atom wants to gain one electron to achieve an octet

Cl Cl do to achieve an octet? What’s the solution – what can they Neither atom will give up an electron – chlorine is highly electronegative. What’s the solution – what can they do to achieve an octet?

Cl Cl do to achieve an octet? What’s the solution – what can they Neither atom will give up an electron – chlorine is highly electronegative. What’s the solution – what can they do to achieve an octet?

Cl Cl octet

Cl Cl octet circle the electrons for each atom that completes their octets

Cl Cl The octet is achieved by each atom sharing the electron pair in the middle circle the electrons for each atom that completes their octets

Cl Cl The octet is achieved by each atom sharing the electron pair in the middle circle the electrons for each atom that completes their octets

Cl Cl This is the bonding pair circle the electrons for each atom that completes their octets

Cl Cl It is a single bonding pair circle the electrons for each atom that completes their octets

Cl Cl It is called a SINGLE BOND circle the electrons for each atom that completes their octets

Single bonds are abbreviated Cl Cl Single bonds are abbreviated with a dash circle the electrons for each atom that completes their octets

This is the chlorine molecule, Cl Cl This is the chlorine molecule, Cl2 circle the electrons for each atom that completes their octets

Naming Covalent Compounds Covalent compounds are named by adding prefixes to the element names. The compounds named in this way are binary covalent compounds. ‘Binary’ means that only two atom are present. ‘Covalent’ (in this context) means both elements are nonmetals. A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.) A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘ide’.

Naming Covalent Compounds Prefixes Subscript Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- Subscript Prefix 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca- Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

Naming Binary Covalent Compounds: Examples 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 heptaa 8 octa 9 nona 10 deca * Second element in ‘ide’ from * Drop –a & -o before ‘oxide’ N2S4 dinitrogen tetrasulfide NI3 nitrogen triiodide XeF6 xenon hexafluoride CCl4 carbon tetrachloride P2O5 diphosphorus pentoxide SO3 sulfur trioxide

Classifying Compounds Classifying a compound using its name is not as difficult as using its formula. The names of covalent compounds will be easily recognized by the presence of the prefixes (mono-, di-, tri-, etc.). If no prefixes are present in the name, the compound is ionic. (Exception: some polyatomic ion names always contain prefixes (such as dichromate) but those will be memorized and recognized as ions.)

Writing Formulas for Covalent Compounds The names of covalent compounds contain prefixes that indicate the number of atoms of each element present. If no prefix is present on the name of the first element, there is only one atom of that element in the formula (its subscript will be 1). A prefix will always be present on the name of the second element. The second element will use the form of its name ending in Remember: The compounds named in this way are binary covalent compounds (they contain only two elements, both of which are nonmetals). When in covalent compounds, atoms do not have charges. Subscripts are determined directly from the prefixes in the name.

Writing Formulas for Binary Covalent Compounds: Examples 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 heptaa 8 octa 9 nona 10 deca * Second element in ‘ide’ from * Drop –a & -o before ‘oxide’ nitrogen dioxide NO2 diphosphorus pentoxide P2O5 xenon tetrafluoride XeF4 sulfur hexafluoride SF6