WRITING AND NAMING IONIC COMPOUNDS

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

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

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

A REMARKABLE FEATURE OF COMPOUNDS FORMED FROM ELEMENTS IS THAT THE PROPERTIES OF THE REACTANT ELEMENTS IS LOST +

THERE ARE 7 OF THESE PAIRED COMBINATIONS A.K.A. DIATOMIC ATOMS SOME CHEM FORMULAS ARE SIMPLE, FOR INSTANCE SOME OF THE GASEOUS ELEMENTS ALWAYS EXISTS IN NATURE AS A PAIR OF ATOMS O-O O 2 H-H H 2 THERE ARE 7 OF THESE PAIRED COMBINATIONS A.K.A. DIATOMIC ATOMS

N 7 O 8 F 9 Cl 17 Br 35 I 53 H 1 H2 O2 N2 F2 Cl2 Br2 I2 HYDROGEN, OXYGEN, NITROGEN, AND THE HALOGENS, ARE ALL DIATOMIC UNDER NORMAL CONDITIONS

WHEN AN ATOM LOSES OR GAINS ELECTRONS IN ORDER TO ACHIEVE ITS OCTET IT FORMS AN ION

THERE ARE ALSO COMBINATIONS OF ATOMS THAT HAVE AN IONIC CHARGE A. K. A THERE ARE ALSO COMBINATIONS OF ATOMS THAT HAVE AN IONIC CHARGE A.K.A. POLYATOMIC IONS P O 4 -3 C O 3 -2 H O -1 N H 4 +1 POLY- MEANS MANY, BUT WE TREAT EACH OF THESE POLYATOMIC IONS AS A SINGLE UNIT WITH A SINGLE CHARGE

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.

AN IMPERFECT ATOM 3s I WANT TO BE PERFECT! - + Ne Na

WHAT DOES SODIUM NEED TO DO TO BECOME LIKE NEON? - + Ne Na IT COULD LOSE AN ELECTRON!

WHAT DOES SODIUM NEED TO DO TO BECOME LIKE NEON? - + Ne - Na IT COULD LOSE AN ELECTRON!

WHAT DOES SODIUM NEED TO DO TO BECOME LIKE NEON? 11 p’s Ne -10 e’s - + +1 charge +1 NOW SODIUM IS MORE STABLE! Na

AN IMPERFECT ATOM I WANT TO BE PERFECT! - + 3s 3p Cl

+ WHAT DOES Cl NEED TO DO TO BECOME LIKE A NOBLE GAS, LIKE Ar? 3s 3p - IT COULD GAIN AN ELECTRON!

+ WHAT DOES Cl NEED TO DO TO BECOME LIKE A NOBLE GAS, LIKE Ar? 3s 3p - IT COULD GAIN AN ELECTRON!

+ WHAT DOES Cl NEED TO DO TO BECOME LIKE A NOBLE GAS, LIKE Ar? 3s - + 17 p’s 3s -18 e’s 3p -1 charge -1 Cl IT COULD GAIN AN ELECTRON!

SO WHAT’S 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.

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

AN ELECTRON IS TRANSFERRED FROM THE Na ATOM TO THE Cl ATOM - + - + Na Cl

BOTH ATOMS ARE HAPPY, THEY BOTH HAVE 8 ELECTRONS IN THEIR OUTERMOST ENERGY LEVEL. THIS IS AN IONIC COMPOUND - + -1 +1 Na Cl

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

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.

PROPERTIES OF IONIC COMPOUNDS CAN CONDUCT ELECTRICITY WHEN MELTED IT FREES UP THE IONS TO MOVE PAST EACH OTHER PACK IN HIGHLY ORDERED ARRANGEMENTS IONS IN A SALT FORM REPEATING PATTERNS CALLED A CRYSTAL LATTICE

PROPERTIES OF IONIC COMPOUNDS HARD PACKED INTO LAYERS, TAKES A LOT OF ENERGY TO BREAK ALL OF THE BONDS BRITTLE IF A FORCE IS STRONG ENOUGH TO REPOS-ITION A LAYER THEN THE REPULSIVE FORCES DRIVE IONS APART

PROPERTIES OF IONIC COMPOUNDS HIGH MELTING POINTS AND BOILING POINTS BECAUSE OF STRONG ATTRA-CTION BETWEEN IONS, IT TAKES A LOT OF ENERGY TO BREAK THEM APART

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

WRITING IONIC FORMULAS THERE ARE A COUPLE OF RULES TO FOLLOW TO MAKE SURE THAT THE PROPER IONIC FORMULA IS WRITTEN.

THE IONS’ CHARGES MUST ADD UP TO ZERO 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

RULE #2 IT’S BETTER TO BE POSITIVE THAN NEGATIVE THE POSITIVE ION IS ALWAYS WRITTEN FIRST. ClNa NaCl

SOME IONIC COMPNDS AUTOMATICALLY HAVE CHARGES THAT ADD UP TO ZERO. K +1 + I -1 KI Mg +2 + O -2 MgO

HOW DO WE DECIDE THE RATIO OF THE IONS? WHAT IF WE WERE FORMING IONIC COMPOUNDS WITH IONS WHOSE CHARGES DIDN’T ADD UP TO A CHARGE OF EXACTLY 0? HOW DO WE DECIDE THE RATIO OF THE IONS?

WHAT IF WE HAD THREE CHLORINE IONS? Al +3 + Cl -1 =2 WHAT IF WE HAD THREE CHLORINE IONS? Cl -1 Cl -1 Al +3 + AlCl 3 Cl -1

IT WILL TAKE 3 Cl-1 IONS TO EQUAL ONE Al+3 ION. WE HAVE A TRICK THAT WILL HELP US KNOW THE NUMBER OF THE IONS TO MAKE A NEUTRAL COMPOUND. IT’S NOT A TRICK SO MUCH AS A SHORTCUT!

CRISS-CROSS RULE: Al +3 + Cl -1 AlCl 3 Ca +2 + P -3 Ca 3 2 P

WITH ONE EXTRA CONSIDERATION. 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.

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.

Al +3 + OH -1 Al(OH) 3 Na +1 4 + SO -2 Na SO 4 2

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

NAMES OF NEGATIVE IONS PARENT ELEMENT NEGATIVE ION CHLORINE CHLORIDE OXYGEN OXIDE NITROGEN NITRIDE PHOSPHORUS PHOSPHIDE FLUORINE FLUORIDE IODINE IODIDE SULFUR SULFIDE BROMINE BROMIDE

NAMING THEM CaCl2  K3P  Al2S3  Calcium chloride Potassium phosphide Aluminum sulfide

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

NAMING THEM FeCl2  FeCl3  PbBr2  Iron(II) chloride Iron (III) chloride Lead (II) bromide

NAMING THEM IF THE COMPOUND HAS A POLYATOMIC ION IN IT 1) NAME THE FIRST ELEMENT 2) THEN NAME THE POLYATOMIC ION

NAMING THEM Fe(OH)2  Ca3 (PO4)2  Na2SO4  Iron(II) hydroxide Calcium phosphate Sodium sulfate

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)

IT’S 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?

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

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

IT TAKES MORE ENERGY TO REMOVE Na’S 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

STEP 1: AT THE BEGINNING THERE IS A CHUNK OF SOLID SODIUM AND A CLOUD OF CHLORINE GAS. Cl Na

A MOLE OF THE SODIUM MUST BE VAPORIZED. STEP 2: A MOLE OF THE SODIUM MUST BE VAPORIZED. Na(s) + ENERGY  Na(g) Na + 110.8 kJ/mol ENERGY IN

Na(g) + ENERGY  Na+(g) + E- STEP 3: AN ELECTRON IS REMOVED FROM EACH SODIUM ATOM TO FORM A MOLE OF SODIUM CATIONS Na(g) + ENERGY  Na+(g) + E- + 495.8 kJ/mol Na + ENERGY IN

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) + 100.8 kJ/mol Cl Cl ENERGY IN Cl

Cl(g) + E-  Cl-(g) + ENERGY 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 + 348.6 kJ/mol ENERGY OUT Cl -1

Na+(g)+Cl-(g)NaCl(s)+ENERGY STEP 6: THE DRIVING THE FORCE OF THE RXN THE Na+1 CATIONS & Cl -1 ANIONS STICK TOGETHER TO FORM A CRYSTAL LATTICE. Na+(g)+Cl-(g)NaCl(s)+ENERGY + 787.5 kJ/mol ENERGY OUT

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

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.

kJ/mol (out) kJ/mol (in) COMPOUND LATTICE ENERGY BOND ENERGY kJ/mol (out) kJ/mol (in) LiCl -861.3 +861.3 LiBr -817.9 +817.9 LiI -759.0 +759.0 NaCl -787.5 +787.5 NaBr -751.4 +751.4 NaI -700.1 +700.1 CaF2 -2634.7 +2634.7 MgO -3760.2 +3760.2