HONORS CHEMISTRY Oct 30, 2013

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.

Notes handout

Why do atoms form bonds? Lewis Dot Diagrams Octet Rule Atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons. Used to illustrate an atoms valence electrons Used to illustrate how electrons rearrange during chemical reactions

Lewis Symbols and the Octet Rule Lewis Symbols: The number of valence electrons available for bonding are indicated by unpaired dots.

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

Why do atoms form bonds? Lewis Dot Diagrams Octet Rule Atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons. Used to illustrate an atoms valence electrons Used to illustrate how electrons rearrange during chemical reactions Na Xe P

Lewis Dot Practice O Te Ca Ba Ne I Cs

Ions and Ionic Compounds Ions are formed by adding or subtracting electrons from a neutral atom or molecule. Cation: positive charge (remove electrons) Na+ Anion: negative charge (add electrons) Cl- Ions may be monatomic or polyatomic 03m07an1&2

Types of Ions Monatomic ions Single atom ions O 2- Na+ Al3+ Polyatomic ions (refer to back of P. table) More than one atom ions NH4 + OH – SO4 2-

Predicting Ionic Charges 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. 3 transition metals with fixed charge (Ag+1, Zn+2 Cd+2) ion_charges.exe http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch12/trans.php

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

Practice on Ionic Charges Pair Share: What is the common charge of an ion of potassium, K? Pair Share: What is the common charge of an ion of sulfur, S?

Why do atoms form bonds? 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 Na Cl Na Cl

Why do atoms form bonds? Mg, S Ca, Br Practice Draw Lewis Dot Structure!!! Metal Non-Metal

What holds Ionic bonds together? Electrostatic Attraction + and - charge

Formation of an Ionic Compound Vd02_007.mov

Properties of Ionic Bonds Ionic bonds are very strong, so separating ions requires much energy High melting points, boiling points Crystals are hard and brittle Electrical insulators when solid, electrical conductors when molten or dissolved in water Demo: electric_pickle.mov

Electrical Conductivity Solid NaCl Liquid NaCl 03s11vd1

Structure and Properties Why are crystalline solids brittle, whereas metallic solids are malleable?

Structure and Properties Brittleness brittle2.mov maleable2.mov

Examples of Ionic Formulas What is the formula of each of these compounds?

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.

Writing Formulas for Ionic Compounds Practice Li and O Mg and O Ca and N Mg and C

Practice Rewrite these incomplete formulas as correct formulas. AlS CaP BaBr Make formulas from the following ions: Mg2+, OH- Fe2+, PO43- Sc3+, O2-

Bonding with a partner You will receive a card with an ion. You will find another person with the opposite charge from you. You will write the ions on your paper and the formula they will create together. Exchange cards and repeat the steps again until you fill up your paper.

Chemical Formulas Remember Combine ions to obtain electrical neutrality Ionic_Formula.exe

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Naming Binary Ionic Fixed Charge Compounds (Formula  Name) Example: Li2O Name the cation Name the anion, changing the ending to ide Lithium Oxygen + ide Lithium Oxide More examples: NaCl CaS AlF3

Naming Binary Ionic Compounds Name  Formula Example: Calcium Chloride Ca +2 and Cl -1 CaCl2 Identify the ions involved List the cation first and then the anion Determine that charge of each ion involved Balance the charges so the compound is neutral (criss-cross method).

Practice Write the structural formula for the following: Hint: separate them into ions and then criss cross Magnesium phosphide Calcium iodide Beryllium oxide

Naming Binary Ionic Compounds STOCK (Transitional Metals) Formula  Name CoCl2 Example: Cobalt (II) chloride Name the cation Determine the charge of the anion Based on the anion, what charge does the cation need to make the compound neutral. Write the cation charge in parenthesis as a roman numeral Name the anion.

Examples Fe3P2 Cu2S NiO

Naming Binary Ionic Compounds Stock (Name  Formula) Example: Calcium Chloride Copper(II) Oxide List the cation first and then the anion Give the cation the charge stated in the name Determine the charge of the anion Balance the charges so the compound is neutral. Ca +2 and Cl –1 CaCl2 Cu + 2 and O –2 CuO

Examples Copper (II) nitride Vanadium (II) oxide Zinc chloride 3 Special Transition Metals (do not require Roman numerals: fixed charge): Zn Cd Ag

Practice Writing Formulas “Transition Metals (stock Method)” wksheet

Naming Ternary Molecular Structures What is a Ternary Molecular Structure? Example MgSO4 Magnesium Sulfate CuSO4 Copper (II) Sulfate A molecule that has more than two elements. A combination of a metal and a polyatomic ion. Same rules as Binary Ionic/Stock but just name the polyatomic

Rally Table NaF K2CO3 MgCl2 Be(OH)2

Practice Worksheet Refer to “Naming Ionic Compounds Practice Worksheet” Make Flash Cards: Polyatomic Ions

Start 11/5/12

Brain Teaser (11/5/12) Write the formula and draw the Lewis Dot structure: Potassium and Phosphorus Name or Write the formula of the following compounds: SrS Cu2S Iron (II) oxide Magnesium cyanide

Agenda (11/5) Brain Teaser Collect Progress Report Grade Practice Ionic Bonding Quiz and WS Questions? Ionic Review Questions Ionic Bonding Quiz Notes: Covalent Bond Homework Study Ionic Compounds Worksheet

Compounds How do we distinguish between ionic and covalent compounds? What do you notice?

Why do atoms form bonds? Covalent bond Shared pair of electrons between two atoms. Non-metal and Non-metal

Lewis Structures Lewis Structures A representation of a molecule that shows how the valence electrons are arranged among the atoms in the molecule * G. N. Lewis Lewis Dot Examples

Why do atoms form bonds? Molecule Diatomic Molecules Super 7 A group of atoms united by a covalent bond A few elements only exist as a pair of atoms never as a single lone atom Cl2, I2, F2, Br2, O2, H2, N2

Round Table – Covalent Bonding SiH4 NH41+ H2Se HCl HF *SO42-

Why do atoms form bonds? Characteristics of covalent bonds Single Bonds Ex. H2 Double Bonds Ex. O2, H2CO Triple Bonds Ex. N2, C2H2 Can form multiple bonds satisfy the octet rule Two atoms share exactly one pair of electrons. Two pairs of electrons shared between two atoms. Three pairs of electrons are shared between atoms

Properties of Covalent Bonds Solids are usually soft low melting points low boiling points Properties arise because molecules are not strongly held together Usually found with nonmetals

Structural Formulas Why do atoms form bonds? Specifies which atoms are bonded to each other Distinguish the difference between substances with the same molecular formula

Structural Formulas Examples See models of different types: Why do we have different types of models?

Structural Formulas A few Models NH3 CO2 How are the atoms connected? H2SO4

Lewis Structure for Super 7’s Draw Lewis structures for super 7’s

Chemical Formulas S8, O2, O3 - What formulas do we find for elements? Elements with different formulas are called allotropes. How many atoms make a molecule? Is there any pattern? xenon oxygen phosphorus sulfur ozone

Brain Teaser Write the Lewis structure for each of the following simple molecules. H2S C2H4 SiF4

Shapes Lab Work with a partner Draw the Lewis Dot Diagrams for each of the compounds Build each of the compounds using the model kits. Sketch the shape of the model Remember all the holes (bonding sites) of each atom must be filled in order for it to satisfy the octet rule.

Shapes of Molecules VSEPR Theory Valence Shell Electron Pair Repulsion System for predicting molecular shape based on the idea that pairs of electrons orient themselves as far apart as possible.

Shapes of Molecules How to use VSEPR theory Examples Total Electron Pairs # of Shared and unshared pairs Shared Electron Pairs # of Pairs involved in covalent bonding Unshared electron Pairs # of Lone pairs of electron Shape or Geometry Linear, bent, trigonal planar, tetrahedral Examples HBr H2O PH3

Shapes of Molecules What do we do with multiple bonds? Count the sides of the central atom that have bonds on them Examples N2 HCN H2CO

Practice Shapes of molecules

THE PASS IT GAME!! You will have one paper for each row. Your job is to do one section and then pass it to the next person. There are three sections: Electron dot, molecular drawing and VSEPR name & angle Once the last person is done raise your hand and get a stamp if all is correct. 1st team will get a prize for each Pass it game!

CCl4

SeO3

BeF2

Polarity of Molecules Electronegativity Polar Covalent Bonds Polar Molecule Ex. H2O Ability to attract electrons Difference in electronegativity tells us who wants the electrons more. Atoms do not share electrons evenly. Atoms with greater electronegativity have a slight negative charge. A molecule is polar if the charge is not evenly distributed

Polarity of Molecules If the 2 atoms have similar electronegativities. What would make a Non-Polar Covalent Bond? Examples F2 PH3 If the 2 atoms have similar electronegativities. The atoms involved exert similar pull on the electrons.

Bond Types and Elctronegativity Electronegativity Difference Bond Type < 0.4 Non- polar covalent Between 0.5 and 1.9 Polar covalent > 2.0 Ionic

Polarity of Molecules Other side of shapes Draw each molecule in its correct VSEPR shape.

Properties Ionic vs. Covalent

Rally Table - Types of chemical bonds