Science Warm-up 9/30/2013 • Describe to me how you feel about the test you got back today. What could you have done differently? What worked for you on this exam? What will you do for the next one? • Your response should be a minimum of 5 sentences and will be left inside of your folders. Thank you for working quietly and individually.
Chapter 20: Chemical Bonds Wood EHS
Section 1: Stability in Bonding • Goals • Describe how a compound differs from its component elements. • Explain what a chemical formula represents. • Explain what the electric forces between oppositely charged electrons and protons are essential to forming compounds. • State a reason why chemical bonding occurs.
A. Combined Elements • Elements combine to create new compounds when the conditions are right.
B. Formulas • A chemical formula tells what elements a compound contains and the exact number of the atoms of each element. • Ex) H20= 2 hydrogen atoms bonded with 1 oxygen atom
C. Atomic Stability • The electric forces between oppositely charged electrons and protons hold atoms and molecules together, and thus are the forces that cause compounds to form. • Atoms of noble gases are unusually stable. • Compounds of these atoms rarely form because they are almost always less stable than the original atoms.
Which is more stable? • Which is more stable on its own and why?
Use the pun to help you identify the element.Give the element’s name and symbol. • “Tasty” part of your mouth • Your brother or mine • What happened to the dinosaurs • Imitation diamond • Warrior Princess • What a dog does to a bone • What doctors do to patients (3) • What you do to a wrinkled shirt • Another name for a policeman • Name of a goofy convict
The answers are … • “Tasty” part of your mouth • Your brother or mine • What happened to the dinosaurs • Imitation diamond • Warrior Princess Tungsten - W Bromine - Br Argon - Ar Zirconium - Zr Xenon - Xe
The answers are … • What a dog does to a bone • What doctors do to patients • What you do to a wrinkled shirt • Another name for a policeman • Name of a goofy convict Barium - Ba Curium – Cm, Helium – He, or Barium - Ba Iron Fe Copper Cu Silicon - Si
Goal of Bonding • The goal of creating a chemical bond is to become more stable than the atom was on its own. • Groups 1-17 fall into this category.
Filling Outer Levels • Atoms fill their outer electron levels by combining with other atoms that are not full either. • As a result, both atoms become more stable than they were before. • Sodium had only one electron in its outer energy level, which it lost to combine with chlorine in sodium chloride.
Reaching Stability • When atoms gain, lose, or share electrons, an attraction forms between the atoms, pulling them together to form a compound. • This attraction is called a chemical bond. A chemical bondis the force that holds atoms together in a compound.
Section 2: Types of Bonds • Goals: • Describe ionic bonds and covalent bonds. • Identify the particles produced by ionic bonding and by covalent bonding. • Distinguish between a nonpolar covalent bond and a polar covalent bond.
Science Warm-up 10/2/2013 • Describe to me how the demonstration works. I want a minimum of 5 sentences, and this will be left inside of your folders. • Thank you for working individually and quietly.
Gain or Loss of Electrons • Elements gain or lose electrons in an attempt to become more stable. • An atom that has lost or gained electrons is called an ion. An ion is a charged particle because the atom now has either more or fewer electrons than protons.
The positive (protons) and negative (electrons) charges are no longer balanced. • the electric forces between oppositely charged particles, such as ions, that hold compounds together.
A Bond Forms • A neutral atom of potassium has one electron in its outer level. This is not a stable outer energy level. • When potassium forms a compound with iodine, potassium loses one electron from its fourth level, and the third level becomes a complete outer level.
The iodine atom in this reaction undergoes change, as well. • An iodine atom has seven electrons in its outer energy level. • During the reaction with potassium, the iodide atom gains an electron, leaving its outer energy level with eight electrons.
This atom is no longer neutral because the atom gained an extra negative particle. • Iodine now has a charge of 1 − and is called an iodide ion, written as I −.
Ionic Bonds • An ionic bond is when two oppositely charged ions are attracted to each other. • This type of bond is typically preceded by a transfer of electrons • However, the compound itself must still hold a neutral charge.
Sharing Electrons • The attraction that forms after sharing electrons is called a covalent bond. • A neutral particle that forms is called a molecule.
Single Covalent Bond • A single covalent bond is made up of two shared electrons.
Multiple Bonds • A covalent bond can also combine multiple electrons. • In order to become stable, nitrogen shares 3 electrons with another nitrogen atom.
Unequal Sharing • Electrons are not always shared equally between atoms in a covalent bond. • The strength of attraction is related to the size of the atom. • The strength is also based on how far away the electron is from the nucleus.
Polar vs. Nonpolar Polar Nonpolar Equal sharing of electrons Means “not having opposite ends” Has an equal charge throughout • Unequal sharing of electrons • Polar means “having opposite ends” • Has a positive and a negative region
Science Warm-up 10-3-2013 • Create a 5 sentence minimum short story that explains this picture.
Once upon a time there was a purple telletubbie. The telletubbie decided that Chinese buffet was for dinner. However, the telletubbie forgot about Charles’ Law. When he got on the plane to go sky diving right after eating it was 112 degrees. His volume expanded and he crashed through the earth.
Section 3: Writing Formulas • Goals • Explain how to determine oxidation numbers. • Write formulas and names for ionic compounds. • Write formulas and names for negative compounds.
Binary Ionic Compounds • A binary compound is one that is composed of 2 elements. • Ex) Potassium iodide = KI • What do you need to know?
Oxidation Numbers • The oxidation number of an element is how many electrons are gained, shared, or lost to become stable. • Ex) Sodium ion= ox. # +1 chloride ion= ox. # -1
Special Cases • Some ions don’t follow the group number theory. These are typically followed by a roman numeral in parenthesis. The number in the parenthesis is the oxidation number.
The group numbers are relative to the oxidation number of most elements.
Compounds are Neutral • Although individual ions carry a charge the compound must carry a neutral charge. • A formula must have the correct number of positive and negative ions so the charges balance. • Ex) Sodium has a +1 charge and chloride has a -1 charge. However, NaCl has a neutral charge.
Writing a Formula • Write the symbol of the element or polyatomic ion that has the positive oxidation number. • Write the symbol of the element or polyatomic ion that has a negative number. • The charge of one ion becomes the subscript of the other ion. • Then reduce the subscripts.
Science Warm-up 10/4/2013 • Describe to me what this quote means to you. Your response should be 5 sentences about whatever this makes you think of. • “We accept the love we think we deserve.” - Perks of Being a Wallflower
Practice • What is the formula for Lithium nitride? • What is the formula for lead (IV) phosphide? • What is the formula for iron (III) oxide? • What is the formula for aluminum bromide? • What is the formula for indium sulfide?
Naming a formula • Write the name of the positive ion. • If the ion is a special ion from before write the charge in a roman numeral. • Write the root name for the negative ion. • Add the ending “-ide” to the root word.
Naming a Formula • Practice • CuCl • CuO • AlCl3 • KCl • Cr2O3
Compounds with Complex Ions • A polyatomic ion is a positively or negatively charged, covalently bonded group of atoms. • Ex) OH-
Compounds with Added Water • A hydrate is a compound that has water chemically attached to the ions
Naming Binary Covalent Compounds • Covalent compounds can bond multiple ways: • N20, NO, NO2, and, N2O5 • All of these would have the same name. • In order to fix this we use Greek prefixes to tell how many ions there are.