WRITING AND NAMING IONIC COMPOUNDS

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WRITING AND NAMING IONIC COMPOUNDS
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ATOMS COMBINE IN SIMPLE WHOLE NUMBER RATIOS TO
BECOME MORE STABLE
THE SMALLEST UNIT OF ATOMIC COMBINATIONS THAT
RETAINS THE CHARACTERISTICS OF THE COMPND IS A
MOLECULE
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THE COMPOSITION OF A MOLE-CULE CAN BE REPRESENTED
IN TWO WAYS AS AN EMPIRICAL OR A MOLECULAR
FORMULA
THE COMPOSITION OF A MOLE-CULE CAN BE REPRESENTED
IN TWO WAYS AS AN EMPIRICAL OR A MOLECULAR
FORMULA
CH2
AN EMPIRICAL FORMULA EXPRESSES THE SIMPLEST RATIO
OF ATOMS IN A COMPOUND
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THE COMPOSITION OF A MOLE-CULE CAN BE REPRESENTED
IN TWO WAYS AS AN EMPIRICAL OR A MOLECULAR
FORMULA
C3H6
A MOLECULAR FORMULA TELLS HOW MANY OF EACH ATOM
ARE PRESENT IN THE COMPND
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A REMARKABLE FEATURE OF COMPOUNDS FORMED FROM
ELEMENTS IS THAT THE PROPERTIES OF THE REACTANT
ELEMENTS IS LOST

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SOME CHEM FORMULAS ARE SIMPLE, FOR INSTANCE SOME
OF THE GASEOUS ELEMENTS ALWAYS EXISTS IN NATURE
AS A PAIR OF ATOMS
THERE ARE 7 OF THESE PAIRED COMBINATIONS A.K.A.
DIATOMIC ATOMS
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H2 O2 N2 F2 Cl2 Br2 I2
HYDROGEN, OXYGEN, NITROGEN, AND THE HALOGENS, ARE
ALL DIATOMIC UNDER NORMAL CONDITIONS
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WHEN AN ATOM LOSES OR GAINS ELECTRONS IN ORDER
TO ACHIEVE ITS OCTET IT FORMS AN ION
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THERE ARE ALSO COMBINATIONS OF ATOMS THAT HAVE AN
IONIC CHARGE A.K.A. POLYATOMIC IONS
POLY- MEANS MANY, BUT WE TREAT EACH OF THESE
POLYATOMIC IONS AS A SINGLE UNIT WITH A SINGLE
CHARGE
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TODAY IS ALL ABOUT COMBINING THESE ELECTRICALLY
CHARGED IONS TOGETHER TO FORM STABLE COMPOUNDS.
REMINDER WHEN TWO ATOMS COMBINE TRANSFERRING
VALENCE ELECTRONS IT IS CALLED AN IONIC BOND.
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AN IMPERFECT ATOM
3s
I WANT TO BE PERFECT!
Ne
Na
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WHAT DOES SODIUM NEED TO DO TO
BECOME LIKE NEON?
3s
Ne
IT COULD LOSE AN ELECTRON!
Na
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WHAT DOES SODIUM NEED TO DO TO
BECOME LIKE NEON?
3s
Ne
IT COULD LOSE AN ELECTRON!
Na
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WHAT DOES SODIUM NEED TO DO TO
BECOME LIKE NEON?
3s
11 ps
Ne
1 charge
1
NOW SODIUM IS MORE STABLE!
Na
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AN IMPERFECT ATOM
I WANT TO BE PERFECT!
3s
3p
Cl
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WHAT DOES Cl NEED TO DO TO BECOME LIKE A NOBLE
GAS, LIKE Ar?
3s
3p
IT COULD GAIN AN ELECTRON!
Cl
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WHAT DOES Cl NEED TO DO TO BECOME LIKE A NOBLE
GAS, LIKE Ar?
3s
3p
IT COULD GAIN AN ELECTRON!
Cl
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WHAT DOES Cl NEED TO DO TO BECOME LIKE A NOBLE
GAS, LIKE Ar?
3s
17 ps
3p
-1 charge
-1
IT COULD GAIN AN ELECTRON!
Cl
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SO WHATS THE BOTTOM LINE?
AN ATOM WILL SHARE, LOSE OR GAIN ENOUGH ELECTRONS
TO BECOME MORE STABLE WITH 8
ELECTRONS IN ITS OUTERMOST ENERGY LEVEL. AND
THEN IT WILL BOND WITH ANOTHER ATOM OF A
DIFFERENT ELEMENT.
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THINK ABOUT IT
FROM OUR PREVIOUS EXAMPLE SODIUM HAD AN EXTRA
ELECTRON AND GAVE IT AWAY TO CHLORINE, WHICH WAS
IN NEED OF ANOTHER ELECTRON. THIS FORMED A BRAND
NEW COMPOUND, NaCl IN WHICH BOTH ELEMENTS WERE
MORE STABLE
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AN ELECTRON IS TRANSFERRED FROM THE Na ATOM TO
THE Cl ATOM
Cl
Na
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BOTH ATOMS ARE HAPPY, THEY BOTH HAVE 8 ELECTRONS
IN THEIR OUTERMOST ENERGY LEVEL.
THIS IS AN IONIC COMPOUND
-1
1
Na
Cl
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OPPOSITELY CHARGED IONS ATT-RACT EACH OTHER AND
FORM AN IONIC BOND THAT IS ELECTRICALLY NEUTRAL,
LOOKING AT THE STRUCTURE OF SALT SHOWS THAT THE
ATTRACTION BETWEEN IONS IS SO GREAT THAT MANY
SODIUM AND CHLORIDE IONS BECOME INVOLVED
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CATIONS ANIONS ARE PULLED TOGETHER IN A TIGHTLY
PACKED STRUCTURE, WHICH GIVES IT A DISTINCTIVE
STACKED SHAPE
THE SMALLEST STACK OF THESE ANIONS AND CATIONS IS
CALLED A UNIT CELL.
UNIT CELLS ARE STACKED TOGE-THER TO MAKE UP A
CRYSTAL LATTICE.
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gypsum
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Calcite
Quartz
Tourmaline

• Halite

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Feldspar
Ruby
Amethyst
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Metallic Bonding
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PREDICTING THE FORMATION OF IONIC CMPNDS
WE CAN PREDICT THE COMBINATIONS OF IONS AND THE
FORMATION OF THEIR IONIC FORMULAS, KNOWING HOW
IONS INTERACT
WE CAN HAVE 2 DIFFERENT KINDS OF IONIC COMPOUNDS
FORMED BINARY OR TERNARY
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WRITING IONIC FORMULAS
THERE ARE A COUPLE OF RULES TO FOLLOW TO MAKE
SURE THAT THE PROPER IONIC FORMULA IS WRITTEN.
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RULE 1
IONS WILL COMBINE IN SMALL WHOLE NUMBER RATIOS
THAT ADD TO GIVE A NEUTRAL COMPOUND.
THE IONS CHARGES MUST ADD UP TO ZERO
3(1) (-3) 0
2 (-2) 0
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RULE 2
ITS BETTER TO BE POSITIVE THAN NEGATIVE
THE POSITIVE ION IS ALWAYS WRITTEN FIRST.
NaCl
ClNa
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SOME IONIC COMPNDS AUTOMATICALLY HAVE CHARGES
THAT ADD UP TO ZERO.
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WHAT IF WE WERE FORMING IONIC COMPOUNDS WITH IONS
WHOSE CHARGES DIDNT ADD UP TO A CHARGE OF
EXACTLY 0?
HOW DO WE DECIDE THE RATIO OF THE IONS?
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2
WHAT IF WE HAD THREE CHLORINE IONS?
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IT WILL TAKE 3 Cl-1 IONS TO EQUAL ONE Al3 ION.
WE HAVE A TRICK THAT WILL HELP US KNOW THE NUMBER
OF THE IONS TO MAKE A NEUTRAL COMPOUND.
ITS NOT A TRICK SO MUCH AS A SHORTCUT!
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CRISS-CROSS RULE
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USING POLYATOMIC IONS
TO WRITE THE FORMULAS FOR COMPOUNDS CONTAINING
POLYATOMIC IONS, FOLLOW THE RULES FOR WRITING
FORMULAS FOR BINARY COMPOUNDS, WITH ONE EXTRA
CONSIDERATION.
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USING POLYATOMIC IONS
WRITE PARENTHESES AROUND THE GROUP REPRESENTING
THE POLYATOMIC ION WHEN MORE THAN ONE OF THE ION
IS NEEDED TO DEVELOP THE PROPER RATIO.
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NAMING THEM
MOST OF THE TIME YOU CAN NAME AN IONIC COMPOUND
BY 1) WRITING THE NAME OF THE FIRST ELEMENT 2)
WRITING THE ROOT OF THE NAME OF THE SECOND
ELEMENT 3) ADDING -IDE TO THE ROOT
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NAMING THEM
CaCl2 ? K3P ? Al2S3 ?
Calcium chloride
Potassium phosphide
Aluminum sulfide
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NAMING THEM
SOME OF OUR METALS HAVE MORE THAN ONE IONIC
CHARGE 1) WE HAVE TO FIGURE OUT WHICH CHARGE THE
METAL HAS 2) THEN WE DESIGNATE THAT PARTICULAR
METAL WITH A ROMAN NUMERAL
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NAMING THEM
FeCl2 ? FeCl3 ? PbBr2 ?
Iron(II) chloride
Iron (III) chloride
Lead (II) bromide
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NAMING THEM
IF THE COMPOUND HAS A POLYATOMIC ION IN IT 1)
NAME THE FIRST ELEMENT 2) THEN NAME THE
POLYATOMIC ION
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NAMING THEM
Fe(OH)2 ? Ca3 (PO4)2 ? Na2SO4 ?
Iron(II) hydroxide
Calcium phosphate
Sodium sulfate
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BONDING BOND ENERGIES
THERE IS A LARGE AMOUNT OF ENERGY STORED IN THE
BONDS OF AN IONIC COMPOUND (INDICATION OF
STABILITY).
THEREFORE, IT TAKES A LOT OF ENERGY TO PULL THE
TWO IONS APART ONCE THEY HAVE ESTABLISHED THEIR
OCTETS AND HAVE BONDED (BOND ENERGY)
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ITS USEFUL FOR SCIENTISTS TO KNOW HOW STABLE THE
BONDS ARE TO DECOMPOSITION.
THEREFORE, SCIENTISTS NEED TO HAVE ACCESS TO THE
BOND ENERGIES OF A VARIETY OF COMPOUNDS.
SO HOW DO WE MEASURE HOW MUCH ENERGY IT TAKES TO
BREAK A BOND?
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• ENERGY IS EITHER RELEASED OR ABSORBED WHEN IONS
  FORM
• FORMING CATIONS REQUIRES AN ABSORPTION OF ENERGY
• THE ENERGY NECESSARY TO REMOVE ONE ELECTRON FROM
  EVERY ATOM IN A MOLE OF Na ATOMS IS 495.8 kJ/mol

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ENERGY IS EITHER RELEASED OR ABSORBED WHEN IONS
FORM

• FORMING ANIONS REQUIRES A RELEASE OF ENERGY
• A MOLE OF Cl ATOMS RELEASES 348.6 kJ/mol WHEN AN
  ELECTRON IS ADDED TO THE OUTERMOST ENERGY LEVEL
  OF EVERY ATOM

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IT TAKES MORE ENERGY TO REMOVE NaS ELECTRON THEN
THE AMOUNT RELEASED FROM Cl ATOMS. SO HOW THEN IS
A MOLE OF NaCl CRYSTALS FORMED? THE FORMATION OF
AN IONIC CRYSTAL
INVOLVES SEVERAL STEPS
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STEP 1
AT THE BEGINNING THERE IS A CHUNK OF SOLID SODIUM
AND A CLOUD OF CHLORINE GAS.
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STEP 2
A MOLE OF THE SODIUM MUST BE VAPORIZED.
Na(s) ENERGY ? Na(g)
ENERGY IN
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STEP 3
AN ELECTRON IS REMOVED FROM EACH SODIUM ATOM TO
FORM A MOLE OF SODIUM CATIONS
Na(g) ENERGY ? Na(g) E-
ENERGY IN
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STEP 4
ENERGY IS REQUIRED TO BREAK THE BOND HOLDING ½
mol OF Cl2 MOLECULES TOGETHER TO FORM A MOLE
OF Cl ATOMS
Cl2(g) ENERGY ? 2Cl(g)
Cl
Cl
ENERGY IN
Cl
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STEP 5
THE NEXT STEP INVOLVES ADDING AN ELECTRON TO EACH
Cl ATOM TO FORM A Cl-1 ANION.
Cl(g) E- ? Cl-(g) ENERGY
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THE DRIVING THE FORCE OF THE RXN
STEP 6
THE Na1 CATIONS Cl -1 ANIONS STICK TOGETHER TO
FORM A CRYSTAL LATTICE.
Na(g)Cl-(g)?NaCl(s)ENERGY
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THE ENERGY RELEASED IN STEP 6 IS CALLED LATTICE
ENERGY, WHICH IS THE ENERGY RELEASED WHEN THE
CRYSTAL LATTICE OF AN IONIC SOLID IS FORMED.

• LATTICE ENERGY IS GENERALLY A NET GAIN IN
  POTENTIAL ENERGY
• A GAIN IN POTENTIAL ENERGY IS A FAVORED CONDITION
• MEASURABLE HEAT ENERGY

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THIS LATTICE ENERGY GIVES US A METHOD OF
MEASURING THE BOND STRENGTH IN IONIC
COMPOUNDS. THE LATTICE ENERGY IS THE ENERGY
RELEASED TO FORM A BOND, AND IS EXACTLY EQUAL TO
THE BOND ENERGY, WHICH IS THE ENERGY TO BREAK A
BOND.
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