Ionic and Metallic Bonding

Why do elements bond with other elements? Elements combine chemically to increase the stability of their electrons Electrons are most stable in groups of 8 (noble gas configuration) Valence electrons can be transferred to another element or shared between elements

Chemical Bonds Force that holds 2 atoms together Different causes for different types of chemical compounds Ionic compounds Ions form when elements gain or lose electrons Ionic compounds form when + ions are attracted to -ions

Electron Configs and Valence Electrons For O 1s 2 2s 2 2p 4 For S 1s 2 2s 2 2p 6 3s 2 3p 4 For Se 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4 For Te 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 4 The red electrons are the valence electrons Same column, similar valence electrons

Groups and Valence Electrons Within a group or column of the periodic table, the number of valence electrons is the same Similar valence electrons cause the elements in a group to react in similar ways

Periodic Table/Bohr Structures

Lewis Dot Structures Show the valence electrons only Valence electrons are the electrons in the outermost energy level Put one dot for each valence electron They don’t pair up until they have to X

Lewis Dots and Periodic Table

Ionic Bonding Transferring of electrons occurs in ionic bonding Ions are formed when electrons are gained or lost by an element Metals lose electrons to form cations (+ charge) Non-metals gain electrons to form anions (- charge) Opposite charges attract to form the final ionic compound

Ionic Bonding How many electrons are gained or lost? It depends on how many electrons are in the valence shell If fewer than 4, electrons are lost expose the lower full energy level of 8 electrons If more than 4, electrons are gained to get to a full energy level of 8 electrons

Predicting Ionic Charges Predict the ion formed for Calcium Potassium Sulfur Aluminum Argon Chlorine Nitrogen Ca 2+ K+ S 2- Al 3+ No ion formed Cl - N 3-

Valence Electrons and Lewis Dots Review Activity Unit3ValenceElectrons.htm Unit3ValenceElectrons.htm

Ionic Bonding Na Cl The metal (sodium) tends to lose its one electron from the outer level. The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose. + -

Ionic Bonding NaCl (1 sodium atom, 1 chlorine atom) Sodium chloride (notice name of chlorine changed) Formula Unit is smallest ratio of ions No single particle of an ionic compound exists Formula Unit is the representative particle for ionic compounds

Crystalline Structure

Ionic Bonding Calcium and phosphorus CaP All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).

Ionic Bonding CaP

Ionic Bonding Ca 2+ P

Ionic Bonding Ca 2+ P Ca

Ca 2+ P 3- Ca

Ca 2+ P 3- Ca P

Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P 3- Ca 2+

Ionic Bonding = Ca 3 P 2 Formula Unit Chemical formula shows the kinds and numbers of atoms in the smallest representative particle of the substance. Calcium phosphide

Ionic Bonding Ionic Compounds are usually made of a metal and 1 or more nonmetals Metals form the + cation Non-metals form the - anion The final compound is neutral because the positive charge is always equal to the negative charge

Energy and the Ionic Bond The formation of ionic compounds always releases energy The reaction is exothermic Exothermic reactions release energy and feel hot

Ionic Crystals Crystal lattice - 3D arrangement of anions and cations Causes the crystalline nature of ionic compounds Lattice energy - energy required to separate the ions of an ionic compound Varies with ion size and charge Smaller ions have larger lattice energies Higher ionic charges have larger lattice energies

Ionic Compounds Properties of ionic compounds High melting points > 300  C High boiling points Crystalline solids at room temperature May dissolve in water but not in non-polar solvents such as oil Conduct electricity when dissolved in water or when melted

Properties of Ionic Compounds Attraction of cations and anions leads to properties Crystalline nature caused by regular repeating pattern of ions Because every ion is surrounded by ions of opposite charge, intermolecular forces are strong so melting and boiling points are high

Properties of Ionic Compounds Many ionic compounds will dissolve in water because of the polar nature of water (like dissolves like) Solutions and melted ionic compounds conduct electricity because ions are free to move in solutions and when the compound is melted

Properties of Ionic Compounds Why are ionic compounds brittle?

Metallic Bonding Metallic Bonding-Type of bonding between metal atoms Metals have high boiling points and melting points-Why? Must be something holding the atoms together Electron Sea Model - Weakly held valence electrons move freely between atoms of metals, holding atoms together

Metallic Bonding Electron Sea Model -

Metallic Bonding ic-bonding-animation.swf ic-bonding-animation.swf

Metallic Bonding Metallic bond is the attraction of a metallic cation for delocalized electrons Electron sea model explains properties of metals High melting points Extremely high boiling points Conducts heat and electricity in solid and liquid state Malleable and ductile luster

Metallic Bonding Mobile electrons help to hold the metal together making metals ductile and malleable

Metallic Bonding Metals conduct electricity as solids and as liquids

Metallic Alloys Mixtures of metals to produce more desirable properties Alloys are still mixtures because electrons are not transferred or shared Examples- Stainless steel, brass, 14 carat gold, mercury amalgams, bronze Bonding is metallic (sea of electrons)

Inquiry Skill Testable Hypothesis Identify independent, dependent and controlled variables

Often Begins with a Question Scientifically Testable Questions Specific, not general Measurable Not opinion or fact Suggest an experiment (what is being changed and what is being measured)

Which are Scientifically Testable Questions? How does exercise affect breathing rate? What is the grading scale used in Chemistry? Will we reach Mars by 2500 AD? Which oil can be used to produce biodiesel with a cloud point of less than 0 C? How does a light bulb work? If the volume of a gas is increased, how does the pressure of the gas change? Testable Not Testable Testable Not Testable Testable

Question Leads to Hypothesis Educated guess about the answer to the question Must be related to the question Must be testable (with an experiment) If (describe the experiment), then (predict the outcome), sometimes because (why you made the prediction)

Which of the following is a good hypothesis? Taking Vitamin C is a good idea. Students who take a daily Vitamin C supplement will get fewer colds than students who do not take the supplement because the Vitamin C will improve their immune system Vitamin C makes students healthier No Yes No

Hypotheses are Tested with an Experiment Controlled Experiment Independent Variable (I change) Dependent Variable (Data) Control Group(Comparison Group) Controlled Variables (All the things that are kept the same between experimental groups)

Identifying Variables Activity w_variables.htm w_variables.htm

Difference between Control and Control of Variables Control - group with is not treated or receives the standard treatment Used as a norm to compare to Control of Variables- procedures designed to make sure that only the independent variable is changing between the experimental groups Only the independent variable changes