Ionic Compounds

Ion Review  Ion: an atom that has gained or lost an electron.  We write an ions as follows: Cl - or Na +  Ions behave differently from the neutral element.

Cation  Cations : ions with a positive charge.  They have more protons than electrons.

Anions  Anions : negatively charged ions.  They have more electrons than protons.  Electron = e -

Noble Gases  Elements want to be like the noble gases.  Every element wants to be stable, thus they want to have a full octet of electrons like the noble gases.

FULL OCTET  Noble gases are stable with a full octet. (octet rule)  Their s and p configurations are full.  s and p have a total of 8 electrons.  Octet: a group of eight.  Ne = [He]2s 2 2p 6

Ionic Compounds  Ionic Compound is any chemical compound composed of oppositely charged ions.  In order to attract, the ions want to create a neutral charge (all the negatives are balanced by the positive)  Al 3+ O 2- is aluminum oxide.  Questions: How would we balance out these charges to be neutral (charge is 0)?

READING IONIC COMPOUNDS  Al 2 O 3  In the example above, the number to the bottom right tells you how many of each ion you have.  The 2 says you have 2 Al +3 ions  The 3 says you have 3 O -2 ions

TRY SOME OF THESE 1. Na + + O Ba +2 + Cl - 3. Fe +3 + O -2

Ionic Compounds  An ionic compound composed of a simple cation and simple anion.  For instance NaCl is a binary ionic compound (has just 2 ions).  Na + + Cl - → NaCl (the charges cancel out)

Losing an electron

NOTICE  In the previous slide, Na now has a full octet

Gaining an electron

REACHING A FULL OCTET  When the Na + lost an electron and the Cl - gained an electron, both ions resemble the stable NOBLE GAS

What holds salt together?  All salts are held together by ionic bonding.  The attraction is so strong that many sodium and chloride ions are pulled together into a tightly packed structure.

What holds salt together?  All salts are held together by ionic bonds.  Halogens that are ions are called halides  All the simple anions formed from group 7.  F -, Cl -, Br -, I -, At -

Energy  Ionization energy is the energy that must be supplied to remove the outermost electron from an atom.  Atoms always resist having their electrons removed.

Energy  What do you think takes more energy to remove an e-  Li  Br  HINT: Draw the shorthand electron configuration. Which ion would be the closest to a noble gas

ANSWER  Li  [He]2s 1  Br  [Ar]4s 2 3d 10 4p 5  If you remove 1 e- from Li, you form the noble gas He  If you remove 1 e- from Br, you don’t form any noble gas  Li is more energetically favorable to lose an e-

GENERAL TRENDS  As you move from left to right on the periodic table, the ionization energy increases  As you go down the periodic table (the quantum number increases), the ionization energy decreases  The electrons are further from the nucleus and not as strongly attracted

GENERAL TREND  As a result of ionization energies, you can predict atomic size:  As you move from left to right, e- are more attracted to the nucleus  THIS MEANS ATOMIC SIZE DECREASES FROM LEFT TO RIGHT  As you move down the periodic table, e- are less attracted to the nucleus  THIS MEANS ATOMIC SIZE INCREASES AS YOU GO DOWN THE PERIODIC TABLE

SUMMARY POINT  Ionization energy and atomic size are opposite  As the ionization energy increases, the atomic size decreases  As the ionization energy decreases, the atomic size increases

Monatomic Ion  Monatomic ion: a simple ion formed from a single atom.  Example: CaBr 2 (charges balance)  Made from Ca +2 and Br -

Polyatomic Ion  Polyatomic ion: a charged group of two or more bonded atoms that functions as a single ion.  Most polyatomic ions consist of atoms of several elements.  Example: K 2 CO 3 (charges balance)  Made from K + and CO 3 -2

ION SHEET  The following handout gives you a lot of information on ions  Name of the ion  Symbol for the ion  Charge associated with the ion

HOW DO YOU CREATE COMPOUNDS WITH POLYATOMIC IONS?  The formation of a compound with polyatomic ions is just like regular ionic compounds  YOU JUST HAVE TO BALANCE OUT THE CHARGE

EXAMPLE  Let’s create the compound with the following ions:  Ba +2 and CN -  To balance out the charges we need:  1 Ba +2, and  2 CN -  Since the CN - is two elements, we have to put a parenthesis around it  Ba(CN) 2

TRY THESE  Na +, SO 4 -2  Fe +3, C 2 O 4 -2  NH 4 +, CO 3 -2

SUMMARY OF STEPS 1. Balance out the charges between each ion. 2. Write down the metal (or the polyatomic ion with the + charge) first 3. Write the number of the ion to the bottom write of the symbol (if it is a polyatomic ion, you must put the entire ion in brackets if there is more than 1)

SUMMARY OF STEPS 4. Write out the symbol for the second ion (either the nonmetal or the negatively charged polyatomic ion) 5. Write the number of the ion to the bottom write of the symbol (if it is a polyatomic ion, you must put the entire ion in brackets if there is more than 1)