Lewis Dot Structures Mr. Garcia

Valence electrons – electrons in an atom’s highest energy level Outermost electrons of the electron cloud Gives elements chemical characteristics Only electrons shown in Lewis electron dot structures Symbolized as dots

Valence Electrons Number of valence electrons is the same as the group number for representative elements Explains why elements of same families have similar characteristics

Valence Electrons Most elements gain or lose valence electrons to have noble gas stability Noble gas stability- Having full outer shell of electrons Example: Sodium react violently with chlorine to make NaCl (table salt).

Drawing Lewis Dot Structures Step 1: Identify the symbol for the element and its number of valence electrons using the periodic table. Step 2: Put the number of electron dots around the symbol. Begin by assigning one dot per side, moving clockwise around the symbol. Start adding a second dot to each side until all of the valence electrons have been placed The four sides represent the four orbitals in the outermost energy level of an atom of a representative element. These electrons are all negatively charged, so they repel each other and will not pair up until there is one electron in each orbital. Dot structures should never have more than two dots on any side.

Lewis Dot Structure - Sulfur Step 1: Find the element and number of electrons Answer: Column number 6 (6 valence electrons) Step 2: Put the number of electron dots around the symbol. Begin by assigning one dot per side, moving clockwise around the symbol. Start adding a second dot to each side until all of the valence electrons have been placed Answer:

Compounds Line up single dots to form compounds and to make either 2 or 8 electrons around each element. The elements share their single unpaired electrons.

Valence electrons and number of bonds Number of bonds elements prefers depending on the number of valence electrons. In general -  F a m i l y # C o v a l e n t B o n d s* H a l o g e n s F , B r C I  X 1 bond often  C a l c o g e n s O , S 2 bond often O  3 bond often N i t r o g e n , P N  4 bond always C a r b o n , S i C The above chart is a guide on the number of bonds formed by these atoms.

Types of Bonds Chemical Bond- mutual electrical attraction between the nuclei and the valence electrons of different atoms Ionic Bonds- electrical attraction between cations(-) and anions(+) Covalent Bonds- the sharing of electron pairs between two atoms

Draw the Lewis Dot Structure for CH3I Step 1: Determine the atoms and the number of each element Answer: One Carbon, Three Hydrogen, and one Iodine Step 2: Write the dot structures for each Answer: Carbon (4 valence e-), Hydrogen (1 valence e-), and Iodine (7 valence e-)

Draw the Lewis Dot Structure for CH3I Step 3: Determine the Total Number of valence electrons to be combined Answer: Carbon 1x4e- =4 electrons Iodine 1x7e- =7 electrons Hydrogen 3x1e- =3 electrons Total: 14 valence electrons Step 4: Form a skeletal structure; if carbon is present put it in the middle. If not, the most electronegative is in the middle. Connect with electron pairs.

Draw the Lewis Dot Structure for CH3I Add unshared electrons to non-metals so they have 8 electrons (except hydrogen). Follows the octet rule. Count the electrons to make sure we used the correct amount and each element follows the octet rule (except Hydrogen)

More on Lewis Structures Electron pairs can also be shown as lines Some chemical compounds have multiple bonds

Draw the Lewis Dot Structure for CH2O Step 1: Determine the atoms and the number of each element Answer: One Carbon, Two Hydrogen, and One Oxygen Step 2: Write the dot structures for each Answer: Carbon (4 valence e-), Hydrogen (1 valence e-), and Oxygen (6 valence e-)

Draw the Lewis Dot Structure for CH2O Step 3: Determine the Total Number of valence electrons to be combined Answer: Carbon 1x4e- =4 electrons Oxygen 1x6e- =6 electrons Hydrogen 2x1e- =2 electrons Total: 12 valence electrons Step 4: Form a skeletal structure; if carbon is present put it in the middle. If not, the most electronegative is in the middle. Connect with electron pairs.

Draw the Lewis Dot Structure for CH2O Step 5: Add unshared electrons to non-metals so they have 8 electrons (except hydrogen). Follows the octet rule. Step 6: Count the electrons to make sure we used the correct amount and each element follows the octet rule (except Hydrogen) 16 Valence electrons WRONG!

Draw the Lewis Dot Structure for CH2O Step 6 (b): If too many electrons are present, add some lone pairs to bond (multiple bonds). When you add an extra bond, remove another lone pair from carbon.

Resonance Structures Compounds that are represented by a variety of ways, multiple Lewis Dot Structures possible. Example Ozone (O3) More Examples: