LECTURE 3.4 – LEWIS STRUCTURES

What are the types of ions that can form?

I. Ions When atoms gain/lose electrons, they gain a charge. Ion – An charged atom due to unequal number of protons and electrons Cation – A positively charged ion Anion – A negatively charged ion

Cats make people feel positive Way to remember the difference between a cation and an anion.

+1 +2 +3 ±4 -3 -2 -1

How do you draw Lewis Structures?

I. Lewis Dot Structures Bohr diagrams take too long to draw Lewis Dot structures only show the valence electrons. Group number (Group 1A, 2A, etc.) tells us the number of valence electrons

Class Example Draw the Lewis structure for fluorine

Table Talk Draw the Lewis Structure for Carbon

Stop and Jot Draw the Lewis structure for Mg. What would the charge of a magnesium ion after the Octet Rule?

How do you show electrons being shared?

Lewis Structures for Ionic Bonds Na Cl

Lewis Structures for Ionic Bonds [Na]+ [Cl]-

Chemical Bonding Ionic Bonds Metallic Bonds CovalentBonds

I. Covalent Bonding This is a bond between only non-metals. In a covalent bond, the electrons are shared between the elements so that each can get an Octet. Most molecules in biology are covalent compounds

II. Drawing Lewis Structures Halogens and hydrogen form only one bond and are located at the end of a molecule. The central atom is always carbon (if it is present) and/or the element that has the lowest electronegativity.

Class Example Draw the Lewis structure for H2S

Table Talk Draw the structure for NH3

Stop and Jot Draw the Lewis structure for C2H6

III. Single, Double and Triple Bonds Elements can share more then one set of electrons. Also can form double and triple bonds. Single bond = 2 electrons Double bond = 4 electrons Triple bond = 6 electrons

Class Example Draw the Lewis Structure for CH2O

Table Talk With your table, draw the structure of C2H2

Stop and Jot Draw the structure of HCN