chemical formulas keynote
TRANSCRIPT
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Writing Formulas and Naming
Ionic & Covalent Compounds
©2005 Douglas GillilandHonors Physical Science @ Sarasota High
Sarasota, Florida
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Chemical CompoundsAn atom consist of a positively charged nucleus (protons
and neutrons) and orbiting electrons.Atoms of elements are not chemically stable until they have 8
electrons (octet rule).Atoms gain, lose or share electrons with other atoms to be
come chemically stable ( have 8 valence electrons ).
8+
Oxygen Atom
Six valenceelectrons.
Not chemicallystable.
8+
Oxide Ion
Eight valenceelectrons.Chemically
stable.
-2
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Types of CompoundsI o n i c - occurs when a metal loses all its valence electrons to a nonmetal. Metal becomes a cation, nonmetal an anion.
C o v a l e n t - two nonmetals share electrons. Neither loses or gains electrons - they share electrons. Neither atom becomes and ion.
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IonicCompounds
Crystalline Lattice
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Burning Magnesium
20+ 8+++2
20+ 8++-2
Magnesium Atom Oxygen Atom Magnesium Ion Oxide Ion+ ! +
2Mg + O2 ! 2MgO
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2Na + Cl2 ! 2NaClReaction between sodium + chlorine
11+ 17+ 11+ 17++ ++ -
Sodium Atom Chlorine Atom Sodium Ion Chloride Ion+ ! +
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Ionic CompoundsIncludes a metal and a nonmetal.
Metal loses e- and becomes a cation (+).
Nonmetal gains e- and becomes an anion(-).
Metal comes first followed by nonmetal.
Change the name of the nonmetal to -ide. Examples: nitride, sulfide, fluoride, oxide, bromide, iodide, chloride, telluride, phosphide.
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Valence electrons are electrons in the outer energy level of an atom.
Metals have between 1-3 valence electrons. Nonmetals have between 5-7 valence electrons.
Lose e- Gain e-
Cations (+ ions)Anions(- ions)
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The valence of an elements is the charge it takes when it loses or gains electrons.
Metal atoms lose electrons and become + ions (cations) Nonmetals gain electrons and become - ions (anions)
+1+2 +3 -4 -3 -2 -1
0
Transition MetalsMultiple valences
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The 5 Steps for writing an ionic compound formula:
Write the symbols of the two elements.
Write the valence of each as superscripts.
Drop the positive and negative signs.
Crisscross the superscripts so they become subscripts.
Reduce when possible.
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Formula for boron oxide
B O1. Write the symbols of the two elements.
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Formula for boron oxide
B O2. Write the valence for each element.
+3 -2
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Formula for boron oxide
B O3. Drop the positive & negative sign.
B O3 2
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Formula for boron oxide
B OB3 2
4. Crisscross the superscripts so they become subscripts.
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Formula for boron oxide
B OB O32
4. Crisscross the superscripts so they become subscripts.
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Formula for boron oxide
B O5. Reduce subscripts when possible. (not possible here)
B O32
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Examples of ReductionCa S !2 2 CaS
Sn O !2 4
Al N !3 3
Ge O !2 4
Be Te !2 3 can’t reduceAlN
Ge O2
SnO 2
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Most Transition elements have 2 valences. Roman numerals are used in the name
to show the valence on the ion.
!" #$% &'() *+ (, -. (/ 0'
12 13 14 15 13 16 16
12 13 12 15 12
16
12
16
12
16
17
Period 4 Transition Metals
Examples:Mn Manganese(IV) Mn Manganese(VI)
Fe Iron(II) Fe Iron(III) Cu Copper(I) Cu Copper(II)
+4 +6
+2 +3
+2+1
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Examples of Transition Metals
Fe +2
Fe +3
Cu+1
Cu+2
Mn+2
Iron(II)Iron(III)
Copper(I)Copper(II)
Manganese(II)Manganese(IV)Mn+4
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Naming compounds with a transition metal.
Iron(III) oxide
Zinc(II) chloride
Silver(I) chloride
Copper(II) phosphide
Lead(IV) sulfidePbS
Fe O
ZnCl
AgCl
Cu P
2
2 3
2
23
Manganese(IV) oxideMnO 2
formula name
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Polyatomic Ions
Polyatomic (many atom) ions are covalent molecules with a charge. They behave as
if they were a single atom ion.
-1
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Polyatomic IonsNH+1
4 AmmoniumSulfate3SO-2HydroxideOH-1SulfiteSO2
-2
Nitrate3NO -1
Nitrite2NO -1
Phosphate4PO -3
Carbonate3CO-2
Treat polyatomic ions as you would any ion - crisscross to determine the formula. The only difference is that when you have more than one of a specific polyatomic ion in a formula
you must encase it in parenthesis.
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Writing Formulas
3NO -1Ca+2
Cation Anion Compound
3Ca(NO )2
Mg +24PO -3
+1Na3 4PO 2Mg ( )
-1OH NaOH+2Ba SO4
-2 SO4BaAs in all ionic compounds you must reduce subscripts, but you cannot change the formula of the polyatomic ion. You can only
reduce subscripts outside the parenthesis.
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Compounds with Polyatomic ionsCarbonate CO3
-2
Calcium carbonate Ca CO3
Aluminum carbonate Al ( )CO3 32
Sodium carbonate Na CO32
4Phosphate PO-3
Sodium phosphate Na PO43
3Calcium phosphate Ca ( ) PO3 2
Aluminum phosphate AlPO 3
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Covalent Compounds
HydrogenAtom
HydrogenAtom
OxygenAtom
WaterMolecule
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Covalent CompoundsTwo nonmetals share electrons so both have 8 valence electrons. Exception: H
Neither takes on a charge - no valence.
Must use prefixes in the name.
Name tells you the formula. Example: N2O4 is dinitrogen tetraoxide.
You cannot reduce the formulas!!!
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Reaction between hydrogen + oxygen2H2 + O2 ! 2H2O
8+
Oxygen Atom2 Hydrogen Atoms
8+
1+
1++1+ 1+
Water Molecule
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Hydrogen
Oxygen
Water Vapor
ExothermicReaction
The Space Shuttle
2H2 + O2 ! 2H2O
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Covalent PrefixesMon - 1Di - 2Tri - 3
Tetra - 4Pent - 5Hex - 6
A prefix tells you the number of atoms of that element
in the compound.
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Examples of Covalent Compounds
Dinitrogen trioxideCarbon tetrahydridePhosphorus pentoxidedisulfur trifluoride
N O2 3CH4
PO5
S F2 3
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Ionic and Covalent StructureIonic compounds form a crystalline
lattice - a repeating pattern of ions. Covalent compounds
form individual molecules that are not connected to
each other.
WaterH atoms
O atom
Boron nitride
N ions-3
B ions+3
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Naming Binary CompoundsDoes the compound have a metal?
Use Roman Numerals to tell the valence of
the metal.
Yes NoIonic
(Metal cation + Nonmetal anion)Place metal first followed by nonmetal ending in -ide
Contain a Transition Metal?Yes No
Examples:sodium chloride
magnesium nitridealuminum fluoride
beryllium oxide
Examples:iron(III) oxide
copper(II) chloridemanganese(IV) oxide
silver(I) chloride
Covalent(Two Nonmetals)
Examples:dinitrogen trioxide, nitrogen trichloride, phosphorus pentoxide, sulfur dioxide
carbon tetrachloride, dihydrogen oxide
Use prefixes to tell the number of atoms in the compound
mon(o)-1, di-2, tri-3, tetr(a)-4, pent(a)-5, hex-6
Place the nonmetal furthest to the left on the periodic table first, then the other nonmetal ending in -ide.
Do not use Roman
Numerals
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Summing up: IonicIonic bonding occurs between a metal and a nonmetal. Metals lose all their valence e- and become cations. Nonmetals gain enough e- to fill their valence level and become anions.
Always crisscross valences and reduce to determine the formulas of ionic compounds
Do not use prefixes in the names.
Ions form a crystalline lattice.
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Summing up: CovalentCovalent bonding occurs when two nonmetals share electrons to fill their valence energy level.
Never use valence to determine the formula - there isn’t any valence. Since the two atoms share electrons, they do not take on a charge.
Always use prefixes in the names.
Atoms combine to form individual molecules.