Unit 4: Ionic, Covalent, and Metallic Bonding Chemistry Pre-AP Calallen High School

Day 1

Bohr Model Drawings-Review What did we learn about the electrons orbiting the nucleus? Is this model technically correct? What does each ring represent? What are the electrons on the outside ring called?

Valence Electrons - Review Valence electrons: found in the outermost energy level (sometimes called a shell) These electrons are used for bonding Example: Nitrogen = 1s2 2s2 2p3 Add up the number of e- (superscripts) in the highest energy level So, nitrogen has 2 + 3 = 5 valence electrons

Valence Electrons - Review

Lewis-Dot Diagrams - Review Lewis Dot Diagrams are a way to represent the valence electrons in an atom. Element’s symbol represents the nucleus and inner-level electrons Dots represent the valence electrons

Lewis Dot Diagram Rules - Reveiw How to draw Lewis Dot Diagrams: Dots are placed one at a time on the four sides of the symbol, then paired until all valence electrons are used… Maximum of 8 e- can be around the symbol d sublevel electrons are not valence electrons – they are in a lower energy level!

Lewis-Dot Diagrams - Review

IONS Examples of atoms: Na Ca I O IONS are charged atoms or groups of atoms with a positive or negative charge. Ions are used to form ionic bonds. To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples of ions: Na+ Ca+2 I- O-2 Examples of atoms: Na Ca I O

Forming Cations & Anions A CATION forms when an atom loses one or more electrons. An ANION forms when an atom gains one or more electrons F + e- --> F- Mg --> Mg2+ + 2 e-

F + e- --> F- Mg --> Mg2+ + 2 e-

PREDICTING ION CHARGES In general metals (Mg) lose electrons ---> cations (+) nonmetals (F) gain electrons ---> anions (-) metals non-metals metalloids

Ions Previously, we have said that the atomic # indicates the number of protons and electrons… The word atom implies a neutral charge Example: Cl has 17 protons and 17 electrons Ions are charged atoms that have gained or lost electrons; Example: Cl- has 17 protons and 18 electrons

Ions Cation – positive ion (+) Anion – negative ion (-) Loses electrons to become more positive Example: Be = 1s22s2 → Be2+ = 1s2 Anion – negative ion (-) Gains electrons to become more negative Example: F = 1s22s22p5 → F- = 1s22s22p6

Practice Determine if the atom gains or loses electrons and if it is a cation or anion. Atom Loose or Gain Ion Cation or Anion? Al O P Br Lose Al+3 cation Gain O-2 anion Gain P-3 anion Gain Br-1 anion

Ion Venn Diagram Cation Anion Negative Charge Positive Charge Generally formed by metals Loses Electrons Al Cu Sn Anion Negative Charge Generally formed by non metals Gains Electrons Br O P Charged Atom Used to form Ionic Bonds

Ions & Lewis Dot Diagrams Lewis dot diagrams for ions have brackets around them with the charge denoted as a superscript Example: O2- = 1s22s22p6 [ O ]2-

Start 3 types of bonds foldable

Day 2

Bonding Occurs Between: Ionic Bonding: Metal + Nonmetal Covalent Bonding: Nonmetal + Nonmetal Metallic Bonding: Metal + Metal

Properties Ionic Bonding Covalent Bonding Metallic Bonding Exhibit a crystal structure Exist as solids Dissolve easily in water Have high melting and boiling points Conduct electricity in solutions Have high electronegativity differences Covalent Bonding Exist as gases, liquids, or solids Do not dissolve easily in water Have low melting and boiling points Do not conduct electricity in solutions Have low electronegativity differences Metallic Bonding Malleable Ductile Conductors of heat Conductors of electricity Must be in the solid state to conduct heat/electricity. Deform under pressure

Crystal Structure of Salts In a solid ionic compound, the structure is called a crystal lattice and contains a regular, repeating, three-dimensional arrangement of ions.

Picture Ionic Bonding Covalent Bonding Metallic Bonding Na Cl e- are transferred! e- are shared! Sea of e-!

Electronegativity Difference Ionic Bonding If EN difference is greater than 1.7 Covalent Bonding 0.5 – 1.7 = polar covalent bond < 0.5 = nonpolar covalent bond Metallic Bonding

Bonding & Electronegativity

Types of Compounds Ionic Bonding Covalent Bonding Metallic Bonding Binary Salts (2 elements) Ternary Salts (3 or more elements) Salts w/ multiple oxidation #s Covalent Bonding Polar covalent compound Nonpolar covalent compound Metallic Bonding

Examples Ionic Bonding Covalent Bonding Metallic Bonding NaCl NaHCO3 (table salt) NaHCO3 (sodium bicarbonate) NaOH (sodium hydroxide) FeCl3 Fe(III) chloride Covalent Bonding Water H2O Carbon dioxide CO2 Metallic Bonding Sterling silver jewelry Brass instruments Bronze materials Stainless steel Metal alloys: Brass: copper and zinc Bronze: copper and tin Stainless Steel: iron and chromium Sterling Silver: copper and silver

Common Ionic Compounds Sodium bicarbonate (NaHCO3) is baking soda used in food, cleaning products, and antacids Sodium chloride (NaCl) is table salt used in food Potassium nitrate (KNO3) is saltpeter used in fertilizer, gunpowder, and food preservatives Sodium hydroxide (NaOH) is lye used in soaps and drain cleaner

Common Covalent Compounds Nitrous oxide (N2O) is laughing gas used as an anesthetic and to boost auto engine power Methane (CH4) is a flammable gas used as fuel and in homes for domestic heating and cooking purposes. Sugars, like sucrose (C12H22O11) and glucose (C6H12O6), are used in food and energy production Hydrogen peroxide (H2O2) is used as a bleaching agent, emetic (induces vomiting), and an antiseptic (clean cuts and scrapes)

Common Covalent Compounds: CO2 Carbon dioxide (CO2) is a gas used by plants during photosynthesis, produced in respiration; it is a byproduct of burning fossil fuels, and it has many uses as a fire extinguisher, refrigerant (dry ice), and carbonation in drinks

Common Covalent Compounds: H2O Water (H2O) is a liquid that is vital for life. It covers about 71% of earth’s surface, and makes up about 60% of the human body. It is known as the universal solvent, and has many unique properties and uses.

Chemical Bonding practice

Day 3

Start with candy compounds

Chemical Bonding Bonds are the attractive force between atoms or ions in a compound and depend upon: The electron configuration (involves valence electrons) Electronegativity Why do elements bond? To achieve a stable electron configuration (8 electrons; noble gas configuration) Octet rule – atoms lose, gain or share electrons to achieve a stable configuration of eight valence electrons To achieve the lowest possible energy state (lowest potential energy)

Formation of Ionic Bonds Ionic bonds occur when valence electrons are transferred from one atom to another – usually between a metal and a nonmetal Cations donate electrons Anions accept electrons Opposite charges make them attracted (bonded) to each other by electrostatic forces

Formation of Covalent Bonds A Covalent Bond occurs when valence electrons are shared between atoms (usually between nonmetallic elements) Covalently bonded compound known as a molecule These shared electrons are part of the valences of all atoms involved (satisfies octet rule) Since electrons are shared, no charges appear Many combinations can occur between two nonmetals Example: carbon and oxygen can form carbon monoxide (CO) and carbon dioxide (CO2) Carbon Dioxide

Single Covalent Bonds A Single Covalent Bond occurs when atoms of some elements attain a noble gas configuration by sharing one pair of electrons between two atoms When drawing these molecules, a line can represent a pair of shared electrons Ex: Methane (CH4)

Multiple Covalent Bonds Sometimes, atoms share more than one pair of electrons between two atoms creating multiple covalent bonds When drawing these molecules, multiple lines can represent pairs of shared electrons Ex: diatomic oxygen (O2) and nitrogen (N2)

Day 4-6: Ionic Bonding Puzzle 2-3 days

Day 7

Molecular Shapes Applies to covalent compounds only. VSEPR steps (valence shell electron pair repulsion): 1) Identify the central atom as the element that can form the most bonds 2) Draw the Lewis dot structure for the molecule 3) Count total # of electron pairs around the central atom 4) Count # of bonding pairs of electrons around the central atom 5) Count # of lone pairs of electrons around the central atom 6) Look at summary chart, identify shape

# of e- pairs around central atom Molecular Shapes # of e- pairs around central atom # of bonding pairs of e- # of lone pairs of e- Name Shape 2 linear 3 trigonal planar 4 tetrahedral 1 trigonal pyramidal angular (bent)

Exceptions to Octet Rule Beryllium Has 2 valence electrons Full with 4 valence electrons Ex: BeI2 Aluminum 3 valence electrons Full with 6 valence electrons Ex: AlCl3 Boron Ex: BH3

Molecular Shape Example What is the shape of water (H2O)? 1) Central atom? oxygen 2) Draw Lewis Dot… 3) # of total electron pairs around central atom? 4 4) # of bonding pairs around central atom? 2 5) # of lone pairs around central atom? 2 6) Refer to chart to identify shape…angular (bent)

Day 8: Covalent Bonding Project

Day 9 -10: PHET Project

End of Unit 4

Types of Electron Sharing Covalent bonds share electrons equally and unequally (“tug of war” with electrons) Which molecule appears “balanced”? Which one does not? H2O O2 Water (H2O) Oxygen (O2)

Unequal Sharing Unequal sharing of electrons occurs when atoms that share electrons have different electronegativities and are called polar bonds Shared electrons spend a greater amount of time at the more electronegative atom Example: water (H2O)

Unequal Sharing Symbols, delta plus and delta minus, represent a partial positive charge and a partial negative charge.

Unequal Sharing Example: H2O Water Molecule Animation http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm

Equal Sharing Equal sharing of electrons occurs in non-polar covalent bonds No difference (or very, very small difference) in electronegativity between atoms that are sharing Example: chlorine (Cl2)

Polar Molecules The effect of polar bonds on the polarity of the entire molecule depends on the molecule shape

Polar & Nonpolar Molecules Polar molecules have a partial positive and partial negative charge – called a dipole Molecules are considered polar if they: Have an asymmetrical shape Some reasons for asymmetricl shape include Has a lone pair of electrons Has Polar Bonds AND has different elements around the central atom

SYMMETRICAL MOLECULES This molecule is non-polar due to the symmetrical shape of the molecule but it does contain polar bonds. YOU CAN HAVE A NON-POLAR MOLECULE AND POLAR BONDS!!! H Polar bonds H C H H

NON-SYMMETRICAL MOLECULES The electrons are no longer being pulled with equal force nor in equal directions. H H C Cl H Different elements

WARNING!!!!!!! Just because you have polar bonds, DOESN’T MEAN YOU ARE A POLAR MOLECULE.

Polar Molecule Practice Is this Polar or Non Polar? Non-Polar H Cl + -

Polar Molecule Practice Is this Polar or Non Polar? Non-Polar BF3 F B

Polar Molecule Practice Is this Polar or Non Polar? Polar net dipole moment H2O H O

Polar Molecule Practice Is this Polar or Non Polar? Polar CHCl3 H Cl net dipole moment

Polar & Nonpolar Molecules *IMPORTANT: Polar & nonpolar molecules are different from polar & nonpolar bonds!!! Non-polar molecules have charges that are evenly distributed, due to shape (ex: any diatomic molecule, gasoline) Polar molecules have a partial positive and a partial negative charge (ex: water)

Be Prepared for Unit 7 Test on 11/18. End of Unit 7 Be Prepared for Unit 7 Test on 11/18.