C HEMICAL C OMPOUNDS Topic 6. C OMPOUNDS What is a compound? A group of 2 or more elements It takes...
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Transcript of C HEMICAL C OMPOUNDS Topic 6. C OMPOUNDS What is a compound? A group of 2 or more elements It takes...
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CHEMICAL COMPOUNDSTopic 6
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COMPOUNDS
What is a compound? A group of 2 or more elements It takes on properties different than those of the
separate elements that compose it
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IONIC AND MOLECULAR COMPOUNDS
Ionic Compounds Are formed when atoms give/take electrons
Molecular Compounds Are formed when atoms share electrons
We’ll look at Ionic Compounds first
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IONIC COMPOUNDS
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PROPERTIES OF IONIC COMPOUNDS
Formed from metals and non-metals Forms ions in solutions Conducts electricity Solid at room temperature
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HOW IONIC COMPOUNDS ARE FORMED
Once an atom give up electrons, it becomes positive
Once an atom takes electrons, it becomes negative
Na9p
Cl11p
9 e- 11 e-
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REMEMBER… Positives and negatives attract Once Na becomes Na+ and Cl becomes Cl- , they are
attracted to each other
Na+ Cl-
9 p 11 p
8 e- 12 e-
Overall charge +1 -1
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CHEMICAL FORMULAS
Chemical formula – uses symbols and numerals to represent the composition of a pure substance.
H2O
Symbol forthe element
hydrogen
Symbol forthe element
oxygen
The small number here
means 2 atoms of hydrogen
No small numberhere means 1
atom of oxygen
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THEORY BEHIND CHEMICAL FORMULAS
CaCl21 ion Ca 2 ions Cl
each ion is +2 each atom is -1 1 x (+2) = (+2) 2 x (-1) = (-2)
(+2) (-2)
Overall charge on the compound = 0
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HOW TO WRITE CHEMICAL FORMULAS WITHOUT ACTING IT OUT OR DOING MATH
If your periodic table has ion charges listed in the corner, look at the ion charge for each element.
Ca+2 and Cl-1
Ca Cl
To become… Ca1Cl2 CaCl2
The superscript should be written as a positive or a negative because the number it’s representing is a number of atoms, not a charge anymore.
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WRITING CHEMICAL FORMULAS
Step Example1. Write the symbol of the metal, then the
non-metalCa Cl
2. Write the number of the charge of the metal as a subscript after the non-metal
CaCl2
3. Write the number of the charge of the non-metal as a subscript after the metal
Ca1Cl2
4. Simplify to lowest terms if applicable. Eliminate any 1s if applicable
Final Answer: CaCl2
Note: The superscript shouldn’t be written as a positive or a negative because the number it’s representing is a number of atoms, not a charge anymore.
Example: What is the chemical formula of the product of calcium and chlorine?
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NAMING IONIC COMPOUNDS
1. The name includes both elements in the compound, with the name of the metal first.
2. The non-metal element is second. Its ending is changed to –ide.
Examples:Calcium chloride (instead of Calcium chlorine)
Magnesium flouride (instead of magnesium flourine)
Sodium iodide (instead of sodium iodine)
Zinc sulfide (instead of zinc sulfur)
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POLYATOMIC IONS
Some ions form when certain atoms of elements combine. These ions are called polyatomic ions. (poly- means “many”).
Polyatomic ions are a group of atoms acting as one.
They combine with metals in the same way that a single atom does.
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WRITING CHEMICAL FORMULAS WITH POLYATOMIC IONS
Chemical formulas are written almost the same as other ionic compounds.
Calcium and nitrate Ca+2 and NO3
-
CaNO3
Ca(NO3)2 why not just CaNO32?
Differences: Brackets must be written around the polyatomic ion to identify that it is acting as one atom
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NAMING COMPOUNDS WITH POLYATOMIC IONS
Naming with a polyatomic ion is very similar to naming compounds between two elements …but easier
Write the name of the metal, then the name of the polyatomic ion. Do NOT change the ending of the polyatomic ion
Examples: Calcium carbonate, sodium nitrate
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MULTIVALENT IONS
Some ions have the ability to give up different amounts of electrons which means that they have two possible charges.
Writing formulas with multivalent ions are done just as they were with an ion with only one charge.
Titanium + Oxygen = Ti2O3
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NAMING COMPOUNDS WITH MULTIVALENT IONS
When writing names with a multivalent ion, you must indicate which version of the element you are using. (The first listed is always more common)
Example: Titanium and oxygen (elements) Ti+3 and O-2 (ions) Ti2O3 (chemical formula) Titanium (III) oxide (name)
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JUST BE CAREFUL WHEN…
Your elements have even numbers of atoms and they have been simplified.
Example: TiO2 = Titanium (IV) oxide
Remember… Titanium (IV) oxide Ti+4 and O-2
Ti2O4 simplified to TiO2
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PRACTICE TIME!
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ANSWERS
Chemical Formula Chemical Name
1. NaCl Sodium chloride
2. BeO Beryllium oxide
3. K2S Potassium sulfide
4. LiF Lithium fluoride
5. CaBr2 Calcium bromide
6. AgI Silver iodide
7. PbCl2 Lead (II) chloride
8. MgO Magnesium oxide
9. BaI2 Barium iodide
10. LiBr Lithium bromide
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ANSWERS
11.
MgCl2 Magnesium chloride
12.
CuO Copper (II) oxide
13.
K2S Potassium sulfide
14.
VBr5 Vanadium (V) bromide
15.
CsI Cesium iodide
16.
MnS2 Manganese (IV) sulfide
17.
MnS Manganese (II) sulfide
18.
AuI3 Gold (III) iodide
19.
Pt3P2 Platinum (II) phosphide
20.
Tl2O3 Thallium (III) oxide
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MOLECULAR COMPOUNDS
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DEFINITIONS Molecule
The smallest independent unit of a pure substance and is generally a cluster of atoms joined together.
Diatomic molecules Molecules made up of two atoms of the same element. These atoms can never be alone, if they aren’t bonded
with another element, they bond with another identical atom.
7+1 Rule: In the shape of a 7 + Hydrogen on the periodic table Nitrogen, Oxygen, Flourine
Chlorine Bromine
Iodine
They create N2, O2, F2, Cl2, Br2, I2, H2
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PROPERTIES OF MOLECULAR COMPOUNDS Composed of two or more non-metals They can be solids, liquids or gases They tend to be insulators, or poor conductors The forces between the molecules are weak bonds They share electrons
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HOW MOLECULAR COMPOUNDS ARE FORMED
Molecular compounds share electrons instead of transferring them. Oxygen has 6 valence electrons Hydrogen has 1 valence electron.
If Oxygen shares electrons with two atoms of hydrogen, oxygen can have 8 electrons and each hydrogen can have 2 electrons – full shells for both Example: Water
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MOLECULAR COMPOUND EXAMPLES
Diatomic molecule
Diatomic molecule
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NAMING MOLECULAR FORMULAS
1. Write the name of the first element.2. Change the name of the second element to end with the suffix
“ide”3. When there is more than one atom in the formula, add a prefix to
indicate the number of atoms. Some are listed below. Exception: When the first element has only one atom, the prefix
mono is not used.
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WRITING FORMULAS FOR MOLECULAR COMPOUNDS
Unless you’re given the name, writing formulas for molecular compounds are tricky because they don’t deal with charges.
Why don’t they deal with charges? Because there are no ions (nothing has given or
taken electrons).
We won’t deal with writing formulas without the names. Just make sure you can convert the name to the chemical formula and back again.
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DRAWING MOLECULAR COMPOUNDS
Glucose Cocaine Propane
Ethanol Caffeine Acetaminophen
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HOWEVER…
All you’ll have to draw is something like this
NH3 H2 BrO2
H H – H
N Br
H H O O
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PRACTICE TIME!!!
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ORGANIZING BONDINGMonovalent Ionic
Multivalent Ionic
Polytomic Ionic
Molecular
Dealing with Electrons
Give/take Give/take Give/take Share
Chemical Formulas
Cross charges into subscripts
Cross charges into subscripts
Cross charges into subscripts – put brackets around polytomic ion
Write the subscript that corresponds to the prefix.
Naming Metal + nonmetal with –ide ending
Metal + Roman numeral indicating charge + nonmetal with –ide ending
Metal + polytomic ion name (no name change)
Turn the subscript number into a prefix name.
Example NaClSodium chloride
AuI3Gold (III) iodide
Au2(CO3)3
Gold (III) carbonate
F2ODifluorine monoxide