CHEMISTRY October 19th, 2011

Welcome Back! October 19th, 2011 Brainteaser: Let’s reflect on last quarter’s performance: What are some things you thought you did well for this class? What are some things you think you could improve for this quarter? What is your overall goal for this quarter (i.e. what do you want to accomplish this quarter and how are you going to do it?)

Agenda Brainteaser Unit 5: Ionic Bonding Notes Homework Ionic Bonding Practice Worksheet

Unit 4: Chemical Bonding Differences in chemical behavior are due to differences in the types of bonds Bond: forces that hold atoms together in molecules or ionic compounds.

Chemical Bonding Types of bonds and types of substances Ionic Covalent Metallic The type of bond between atoms is partially responsible for the properties of the substance.

Chemical Bonding Bonding Involves the valence electrons or outermost shell (or highest shell) electrons For group A elements – the group number tells how many valence electrons For example: K, Ca, C, B, N, F, Ne Lewis Dot Structures show the valence electrons around an atom and for most molecules and compounds a complete octet for the elements is needed. For example: N, Al, H2O

Lewis Dot Structures These symbols are called Lewis symbols  We generally place the electrons on four sides of a square around the element symbol.

Drawing Lewis Dot Structure Place DOTS around the SYMBOL clockwise pairing up dots on the second time around For example: Magnesium (Mg) and Oxygen (O)  MgO Mg O

Ionic Bonding

Ions and Ionic Compounds Ions are formed by adding or subtracting electrons from a neutral atom or molecule. Cation: positively charged ions (remove e-) Anions: negatively charged ions (add e-)

Two Types of Ions Monatomic ions Polyatomic ions Single atom ions Al3+ Polyatomic ions More than one atom ions NH4 + OH – SO4 2-

Predicting Charges of Ions Electron Counts of Stable Ions Ions tend to have the same number of electrons as the nearest noble gas. Transition metals are not as predictable, but +2 and +3 are common.

Main Group Elements Note periodicity of charges

Transition Elements Not periodic; +2 and +3 common

Charges and Formulas of Oxoanions Oxoanions generally have the same charge as the simple anion of the same nonmetal. Related to position in the periodic table; note exceptions for B, C, N Polyatomic Ions tend to reflect the charge of the base element

Ionic Bonds form when… A cation (metal) bonds with an anion (nonmetal) A salt is formed: For example: Sodium: Na “metal” bonded to Chlorine: Cl “nonmetal” For example: Magnesium: Mg “metal” bonded to Chlorine: Cl “nonmetal”

Ionic Bonding: The Formation of Sodium Chloride Sodium has 1 valence electron Chlorine has 7 valence electrons An electron transferred gives each an octet Na: 1s22s22p63s1 Cl: 1s22s22p63s23p5

Ionic Bonding: The Formation of Sodium Chloride This transfer forms ions, each with an octet: Na+ 1s22s22p6 Cl- 1s22s22p63s23p6

The resulting ions come together due to electrostatic attraction (opposites attract): The resulting ions come together due to electrostatic attraction (opposites attract): The resulting ions come together due to electrostatic attraction (opposites attract): The resulting ions come together due to electrostatic attraction (opposites attract): Na+ Cl- Na+ Na+ Cl- The net charge on the compound must equal zero The net charge on the compound must equal zero

Lewis Dot Drawing Ionic bond Example Lewis Dot diagram A positively charged ion is attracted to a negatively charged ion. A transfer of electrons Metal and a Non-Metal NaCl A positively charged ion is attracted to a negatively charged ion. A transfer of electrons Metal and a Non-Metal NaCl A positively charged ion is attracted to a negatively charged ion. A transfer of electrons Metal and a Non-Metal NaCl Na Cl

Practice Draw the Lewis dot structures for the following compounds: CaO BaCl2 Na2S

Writing Formulas for Ionic Compounds Crisscross Method Example: Ca and F Write the element symbols for the cation and anion, with the cation on the left and the anion on the right. Write each ion’s charge as a superscript. Crisscross the two charges moving them downward diagonally from one superscript to the other subscript.

Practice Write the correct formula for the ionic compounds composed of the following pairs of ions using the crisscross method: Potassium and iodide Magnesium and chloride Aluminum and bromide Cesium and nitride Barium and sulfide Iron (II) and fluoride

CHEMISTRY October 20th, 2011

Warm Up Write the correct formula for these ionic compounds: Aluminum oxide Barium nitride Iron (III) oxide Magnesium carbide

Agenda Brainteaser Grade Homework: Practice W/S Unit 5 Notes: Naming Ionic Compounds Properties of Ionic Compounds Partner Bonding Activity Homework: Naming Ionic bonds W/S

Naming Ionic Compounds Step 1: Cation is written first in the name; anion is written second in the name Name of cation is the same as the neutral atom element (Na+ = Sodium) Step 2: Anion is written by adding the suffix –ide to the root of the element name (I- = iodide) For example: NaCl = Sodium Chloride, Al2O3 = Aluminum oxide Step 3: Figure out if you need a Roman numeral in the name (transition metals). Figure out what the Roman numeral should be For example: Fe2O3 Step Four: Check your work http://misterguch.brinkster.net/ionic.html

Practice Naming Ionic Compounds KF AlF3 KCl Na3P Fe2O3

Properties of Ionic Bonding Definition: In an ionic bond, a positively charged ion is attracted to a negatively charged ion Electrostatic Attraction

Properties of Ionic Bonding Solid at room temperature Electrical conductivity Conducts electricity when dissolved in water or in liquid (molten) form Dissociated ions can carry charge through the solution Hardness Hard but brittle Electrostatic repulsion Melting points and Boiling points High melting and boiling point Forces of attraction between positive and negative ions are strong

Properties of Ionic Bonding

Quiz Write the chemical formula for these ionic compounds: Sodium bromide Potassium nitride Beryllium phosphide Write the chemical names for these ionic compounds SrCl2 MgI2 Ba3N2