Chem Catalyst These diagrams are called Lewis dot

Chem. Catalyst These diagrams are called Lewis dot symbols. 1. What is the relationship between the number of dots, the number of valence electrons, and the HONC 1234 rule? 2. Create a Lewis dot symbol for fluorine, F. How many bonds will fluorine make?

Draw the Lewis dot structure for the following elements (write e- config first): 4 valence e- Si 1 s 2 2 p 6 3 s 2 3 p 2 O 1 s 2 2 p 4 6 valence e- P 1 s 2 2 p 6 3 s 2 3 p 3 5 valence e- B 1 s 2 2 p 1 3 valence e- Ar 1 s 2 2 p 6 3 s 2 3 p 6 8 valence e- Br 1 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 10 4 p 5 7 valence e-

Key Question How does one atom bond to another in a molecule? You will be able to: • create accurate structural formulas using Lewis dot symbols • describe the type of bonding found in molecular substances • explain the chemistry behind the HONC 1234 rule

Prepare for the Activity Lewis dot symbol: A diagram that uses dots to show the valence electrons of a single atom.

Discussion Notes You can use Lewis dot symbols to create Lewis dot structures. A covalent bond is the sharing of a pair of electrons between two nonmetal atoms. Some valence electrons are not involved in bonding. Bonded pair: A pair of electrons that are shared in a covalent bond between two atoms. Lone pair: A pair of valence electrons not involved in bonding within a molecule. The two electrons belong to one atom.

Let’s bond two F atoms together… Each F has 7 v. e– and each needs 1 more e– F F F 2 Now let’s bond C and F atoms together… carbon tetrafluoride (CF 4) F F C F F

Lewis Structures: 2 D Structures NH 3 CH 2 O CO 2 SO 2 CH 4

Drawing Lewis Structures 1. Sum the # of valence electrons from all atoms Anions: add e– (CO 32 - : add 2 e– ) Cation: subtract e– (NH 4+: minus 1 e– ) 2. Predict the arrangement of the atoms • Usually the first element is in the center (often C, never H) 3. Make a single bond (2 e–) between each pair of atoms 4. Arrange remaining e– to satisfy octets (8 e– around each) • Place electrons in pairs (lone pairs) • Too few? Form multiple bonds between atoms: double bond (4 e– ) and triple bond (6 e– ) 5. Check your structure! ✓ All electrons have been used ✓ All atoms have 8 e. Exceptions: Remember that H only needs 2 e– !

Lewis Structure Practice Draw a Lewis Structure for the following compounds: CH 4 OF 2 H 2 O HCN NF 3 NO 3 - HBr CO 32 - H C N

Lewis Structure Trends Here are some useful trends… C group • Forms a combo of 4 bonds and no LP (Lone Pairs) • i. e. CO 2 N group • Forms a combo of 3 bonds and 1 LP • i. e. NH 3 O group • Forms a combo of 2 bonds and 2 LP • i. e. CH 2 O F group (halogens) • Forms 1 bond and 3 LP • i. e. OF 2 Note that these are NOT always true!

Now You Try on your MATS! ~ You can check answers on the keys in the center of your pods ~There are SOME exceptions to the OCTET rule. . . BSF PBr 3 HBr N 2 H 2 C 2 H 5 OH (ethanol) CH 3 OH (methanol) N 2 F 4 NO 2 -1 SF 6 C 2 H 4

Wrap Up How does one atom bond to another in a molecule? • A covalent bond is a bond in which two atoms share a pair of valence electrons. • Lewis dot symbols show the valence electrons in an atom and are used to predict bonding in a molecule.

Wrap Up (cont. ) • In a Lewis dot structure, a pair of electrons that are shared in a covalent bond is called a bonded pair. Pairs of electrons that are not involved in bonding and belong to one atom are referred to as lone pairs. • The HONC 1234 rule indicates how many electrons are available for bonding in atoms of hydrogen, oxygen, nitrogen, and carbon.

Check-In The molecular formula C 4 H 10 O has seven different isomers. Draw the structural formula of one of them. You can use your puzzle pieces to assist you.