8.1 Covalent Bonds

Molecular compounds = 2 non metals that share 1 or more pairs of electrons… group is electrically neutral.

Draw the dot structure for CF 4

A dash shows a molecular bond and represents 2 electrons

How is water (H 2 O) different from sodium chloride (NaCl)?

Review Bond Types: Copy into powerpoint notes. IONIC: Metal and Non Metal ions. Electrons jump from metal to non metal to make “magnets”. METALLIC: Metal and Metal ions. Electron sea floats between positive ions. CoVALENT: Non Metal and Non Metal atoms (Not ions). Share electrons.

IONIC review: NaCl=Formula Unit=lowest ratio of ions in an ionic compound -atoms gained or lost e- to form ions that are electrostatically bonded to each other (metal)

H 2 O =Molecular Formula= (Nonmetals) molecule atoms share electrons to form stable noble gas configurations (atoms don’t form ions but still follow the octet rule) H=2 electrons

Notice the octet rule H = He 2e- O=Ne 8e-

Molecular formula = shows the number and types of atoms in a molecule Discuss VESPER Theory and shapes of these molecules (electron pairs make 4 point pyramid). Discuss the Lewis Structures.

How is the molecular formula different from a formula unit? Covalent Bond Ionic Bond

Sharing 2 or 3 pair of electrons

Sharing 2 pairs of electrons

Draw the compound CO 2

Bond dissociation energy = amount of energy needed to break a single covalent bond

The higher the BDE the stronger and more stable the bond.

7 diatomic elements found on earth H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 Diatomic elements: 7,

VSEPR = valence-shell electron- pair repulsion theory. Causes shape of molecules. repulsion between electron pairs causes molecular shapes to adjust so that the valence-electrons pairs stay as far apart as possible (SEE p242)

Polar bonds : electron pair is shared unevenly. Causes the molecule to act like a magnet. (the element with higher electronegativity (p.xxx) has the electron more often and become slightly negative)

Subtract the electronegativity of the two atoms to find the type of bond. (pg 248) Bond Type Nonpolar covalent Moderately polar Very Polar Ionic or Metallic

Hydrogen Bonds – hydrogen bonded to an atom with a high electronegativity is weakly bonded to a nearby molecules unshared electrons

Bond Type p.238 table 8.3 Electronegativity Difference nonpolar covalent polar covalent metal = Ionic

Polar molecules – a molecule that has two poles (positive and negative, only happens with polar bonds) based on VSEPR shape

Label bond type on worksheet Identify VSEPR shape Identify polar molecules

POLYATOMIC IONS: Sharing too many electrons… Polyatomic ions (molecules with a charge)

Review

Draw the compound SCl 2

Molecules: Covalent Sharing of Electrons