ionic and metallic bonding. why do elements bond with other elements? elements combine chemically to...
TRANSCRIPT
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
1s2 2s2 2p4
For S 1s2 2s2 2p6 3s2 3p4
For Se 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
For Te 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p4
The red electrons are the valence electronsSame 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
Ca2+
K+
S2-
Al3+
No ion formed
Cl-
N3-
Valence Electrons and Lewis Dots Review Activity
http://www.sciencegeek.net/Chemistry/taters/Unit3ValenceElectrons.htm
Ionic Bonding
Na ClThe 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
Ca PAll the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).
Ionic Bonding
Ca P
Ionic Bonding
Ca2+ P
Ionic Bonding
Ca2+ P
Ca
Ca2+ P 3-
Ca
Ca2+ P 3-
Ca P
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+P
3-
Ca2+
Ionic Bonding
= Ca3P2Formula 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 http://www.drkstreet.com/resources/metallic-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
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 http://www.execulink.com/~ekimmel/udraw_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