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I want you to meet a friend of mine?Bonding, the way atoms are attracted to each other to form molecules, determines nearly all of the chemical properties we see. And, as we shall see, the number “8” is very important to chemical bonding.
5.1 What are Molecules?
Molecules are a combination of atoms
bonded together. Bonding determines the chemical
properties of the molecule (compound).
VALENCE ELECTRONS
The number of valence electrons determines the chemical properties of an element
Electrons that engage in bonding to form molecules and compounds
Groups - Review
• Each column is called a “group”
• Each element in a group has the same number of electrons in their outer orbital, also known as “shells”.
Group 1 = 1 electron
Group 2 = 2 electrons
Group 8 = 8 electrons
Except for He, it has 2 electrons
• The electrons in the outer shell are called “valence electrons”
www.chem4kids.com
3, 4, 5, 6, 7
Octet rule
Group 8 – noble gasesHave 8 valence electronsStable and unreactive in chemical reactionsAtoms will react with each other in order to
attain 8 valence electrons ( octet=8)Gain or lose electrons – ionsShare electrons
Lewis Structures – visually show valence electrons
1) Find your element on the periodic table.
2) Determine the number of valence electrons.
3) This is how many electrons you will draw.
Lewis Structures
1) Write the element symbol.
2) Carbon is in the 4th group, so it has 4 valence electrons.
3) Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol.
C
IONIC BONDING FORMING CATIONS AND ANIONS
• Atoms are electrically neutral due to equal numbers of electrons and protons
• Ions which are charged particles form when atoms or groups of atoms gain or lose electrons to form compounds
• Want to have an octet or be like the noble gases
• Oxidation numbers are assigned to keep track of electrons that are lost or gained
IONIC BONDING FORMING CATIONS AND ANIONS
ANION = O becomes O-2 is an oxygen ion
Oxidation number is -2 O will gain 2, (valence = 6) has more electrons that protons = negative
overall
CATION = Na becomes Na+ - Na ion
Oxidation number is +1 Na will give up 1, will never gain 7Has more protons than electrons = positive
overall
The positive and negative ions are attracted to each other electrostatically.
Formation of Ionic Compounds
Formula UnitsA chemical formula shows the kinds and numbers
of atoms in the smallest representative unit of a substance.
EX. NaCl, MgCl2
A formula unit is the lowest whole-number ratio of ions in an ionic compound.
NaCl ( 1:1), MgCl2 (1:2)
7.2
REVIEW QUIZ
How many valence electrons are in K ( potassium) Mg (magnesium)
Draw the lewis dot structure for the above
3 points each1 = formula1 = correct symbol1= lewis dot and correct depiction of bonding
Al + Br
NAMING IONS
Compounds have a positive metal ion and a negative nonmetal ion combined together to form a neutral compound
Monatomic ions = single atom with a positive or negative charge resulting from a loss or gain of valence electrons
NAMING CATIONS
The names of cations are the same as the metal followed by the word ion or cationEx. Na + = sodium cation (ion)Al 3+ = aluminum cation (ion)
NAMING ANIONS
Nonmetals gain electrons forming anionsNaming
Start with the stem of the element nameAdd –ide
Ex. Chlorine = Chloride ionSulfur = Sulfide ion
Diatomic Compounds
Use the full name of the cation (metal) written first
The anion (nonmetal) comes last and change ending to –ide
Sodium Chloride Potassium Nitride
TRANSITION METAL IONS
Can form more than 1 cationEx. Fe can lose 2 e- or it can lose 3 e-These metals are designated by a roman
numeral in parenthesis Fe (II) ionIf the metal has only one ionic charge you
would not use a (I).
Writing Formulas From Names Identify the charge of the cation Identify the charge of the anionCriss Cross oxidation numbers to become
the subscripts in the formula
Aluminum Sulfide Al3+ S2-
Al2S3
POLYATOMIC IONS
Group of atoms that stay together and have a charge.
ex. Sulfate anion = SO4 2-
Different endings depending on the number of o (oxygen) in the atom
ex. NO2 – = nitrite NO3 - = nitrate
POLYATOMIC IONS
Create a notecard the lists the names of polyatomic ions
This may be used on tests-if you forget it, you are out of luck !!!
Page 257 table 9.3
Review Quiz
Using correct oxidation numbers write the chemical formula of the followingAluminum OxideZinc Nitrate
Correctly name the following compoundsCu3 P
Mn2(SO3)3
PROPERTIES OF IONIC COMPOUNDS
Most are crystalline solids at room temperatureArranged in repeating 3-D patterns
MELTING POINTS
Generally very high melting points
Due to very large attractive forces between ions and crystal formation
Review Quiz
Write the following formulasMagnesium oxideSodium sulfideTin (II) flouride
Name the following compoundsMnO2
CuCl2Li3N
METALLIC BONDS/PROPERTIES
Occur between two metalsGood conductors because electrons can
flow freely Crystalline structureMetals are arranged in a very compact
and orderly fashion
ALLOYS
Most metals are alloys - mixture of two or more elements with at least one being a metalEx. Brass, sterling silver, stainless steel, cast
ironUsually more durable, harder ect..