Download Ionic Compounds Unit NOTES

Ionic Compounds Unit NOTES Name ______________________ Period__
LEWIS DOT STRUCTURES OF ATOMS
“Lewis Dot Structures are sometimes called Electron Dot Structures.”
The one’s digit of an element’s group number tells how many
valence electrons an element has. (FOR STEP #2 BELOW.)
Order to draw
electrons in Lewis
Dot Structures:
Valence electrons are the outermost electrons in an atom. These are
1 2
3 Element 5
6 Symbol 8
4 7
the electrons on the outer shell, which is the highest energy level.
HOW TO DRAW A LEWIS DOT STRUCTURE FOR ANY ELEMENT:
1) In the center of the Dot Structure, write the element symbol.
2) Draw the dots to represent the valence electrons the element has.
3) Follow the pattern for drawing the valence electrons.
Here are some already drawn correctly:
Drawing the valence electrons in this order helps us to understand WHY atoms lose or gain electrons.
(SEE THE OCTET RULE & OXIDATION NUMBER information that follows...)
OCTET RULE
The maximum number of valence electrons is 8 . If an atom does not have “8” valence electrons, it will
react with other elements to become stable…..
The Octet rule says:
“Atoms will either lose, gain, or share valence electrons in order to obtain
a full set of eight (8) valence electrons.”
One exception to the octet rule: Helium only has two electrons. Helium’s only energy level
is full. We show them as a pair.
He:
Helium is stable (not reactive).
REVIEW STRUCTURE OF ATOMS….
The nucleus is made of protons and neutrons.
Since protons are positive and neutrons are neutral, the whole nucleus has a positive charge.
Electrons have a negative charge.
Since electrons are negative, the entire electron cloud is negative.
Atoms are neutral when the number of protons EQUAL the number of electrons.
What makes a neutral atom of :
Boron: protons ( 5p+ ) neutrons (11-5 = 6 no)
electrons (5 e-)
Fluorine: protons ( 9p+ ) neutrons (19-9 = 10 no)
NOTES PAGE 1
electrons (9 e-)
OXIDATION NUMBERS
OXIDATION NUMBER is a fancy way to say “charge”.
1. If an atom has 8 protons in its nucleus, what is the charge on the nucleus?_________
2. If an atom has 8 electrons, what is the charge on the electron cloud? __________
3. If an atom gains electrons to form a bond with another element, it will have more electrons than
when the element is neutral.
An atom that has gained electrons has a (positive / negative ) charge.
4. An atom that loses electrons has more protons than electrons & a (positive / negative ) charge .
5. If an atom has not gained or lost electrons, its charge is ____________ & its oxidation number is ___.
How to determine the oxidation number (charge) of an element:
KNOW THIS whole chart WELL !!!!!
MEMORIZE THIS !!!!!
Group
Number of
valence electrons
1
1
Is this amount closer
to “zero” or “eight” ?
Zero
2
2
Zero
Lose
2 e-
+2
13
3
Zero
Lose
3 e-
+3
14
4
In the middle
15
5
eight
GAIN 3
e-
-3
16
6
eight
GAIN 2
e-
-2
17
7
eight
GAIN 1
e-
-1
18
8
8 is eight!
ELEMENT
EX. beryllium
Group
2
Lose or Gain electrons &
HOW many
Lose 1 e-
Can lose or gain !
Does not lose or gain
Number of
valence electrons
2
Number of electrons
(gain or lose?)
LOSE 2e-
a. aluminum
b. phosphorus
c. tellurium
d. neon
NOTES PAGE 2
Oxidation Number
+1
+4
or
-4
0—stay neutral
Oxidation
Number
+2
FORMING IONIC BONDS—HOW & WHY
An ionic compound is made of metal & a nonmetal held together with an ionic bond.
Ionic Bonds always involve the transfer of electrons from a metal to a nonmetal.
They do this so that each may obey the Octet Rule.
For Example:
• The most famous “salt” of all!
Actually, any ionic compound is a salt!
• The outer electron of the sodium transfers to the chloride
• Then, the oppositely charged particles stick together by
static electricity.
Metals form Cations
Metals almost always lose their outer electrons, forming positive cations:
Na  Na+1 + 1 electron
Ca  Ca + 2 electrons
+2
Al  Al+3 + 3 electrons
Cations are positive because
After losing electrons, there are more
“positive” protons than “negative” electrons.
Each time a metal loses the outermost valence electrons, the energy level below is full.
Nonmetals form Anions
Nonmetals almost always gain electrons, and become negative anions.
Cl + 1e-  Cl-1
Chlorine now has 18 e, just like Argon!
O + 2e-  O-2
Anions are negative because
N + 3e-  N-3
After gaining electrons, there are more
“negative” electrons than “positive” protons.
Each time a nonmetals gains the number of electrons needed to obtain 8 valence electrons.
NOTES PAGE 3
What is the name for a nonmetal when it is part of a compound?
ELEMENT
name when alone
Carbon
ION NAME
Element
name when alone
Ion Name
carbide
Sulfide
Nitrogen
Chlorine
Oxide
Selenide
Fluoride
Bromine
Phosphide
Iodide
What are BINARY COMPOUNDS ?
Binary- means 2 parts.
Binary Compound = just two elements are present.
The hardest thing to remember for most binary compounds is that the name of the nonmetal changes when
it is part of a compound. (See the chart above.)
“Phosphorus” is simply “P” and is the element in its pure form.
“Phosphide” is P-3 and is actually part of a compound such as Na3P
WRITING FORMULAS OF BINARY COMPOUNDS
∎ Follow the steps! ∎“Almost right” is wrong!
∎ Use the symbols as they are written on the periodic table. (PROPER LETTERS)
Use first grade writing rules: Capital letters are generally taller than lower case letters.
“That’s how I write” will not change your grade or your incorrect writing on symbols
∎ Do not guess.
and formula writing. Why does it matter? ( Co =cobalt
Cs = cesium CS = carbon sulfide
Cu ≠ CU)
CO = carbon monoxide
Improper symbols will LOSE POINTS.
STEPS FOR WRITING FORMULAS:
1) WRITE the symbols & oxidation numbers (charges) for the elements in the name.
2) Criss Cross & reduce…. Multiply by the number that will make the charges match
( If the charges ALREADY match
“multiply by 1” on both elements !!!)
3) The number you multiply by IS the subscript in the formula. (NO CHARGES on SUBSCRIPTS.)
(Please remember: a subscript is written smaller than letters & lower than letters on the line.)
Ex1. sodium phosphide
Na +1
+1 x 3 = +3
P-3
-3 x 1 = -3
Ex 2. Radium phosphide
OR
Na3P
Ra3P2
+2
Ra
P
+2 x 3 = +6
EX 3. Indium phosphide
Na3P1
In+3
+3 x 1=+3
-3
-3 x2 = -6
P -3
+3 matches -3
-3 x 1 = -3
x 1 on both!!
NOTES PAGE 4
In3P3 In1P1 OR InP
REDUCE subscripts
CLASS PRACTICE WRITING BINARY FORMULAS
Compound Name
Ions & Oxidation # HOW TO SHOW WORK
Final formula
barium fluoride
cesium nitride
aluminum selenide
What are POLYATOMIC COMPOUNDS?
Ammonium = NH4+1 .
Nitrate, Nitrite, Nitride...which one is just the nitrogen ion?
Look on the “polyatomic ion list” behind your periodic table. What is Nitrate? ____ What is Nitrite?___
A polyatomic compound is a compound that contains at least one polyatomic ion.
∎An easy way to recognize the name of a polyatomic compound:
The first name is ammonium OR the second name ends with -ite or ate. (with the exception of
Cyanide and hydroxide which are also polyatomic ions-- they are ions made of more than one element.
STEPS FOR WRITING polyatomic compound FORMULAS:
1) WRITE the symbols & oxidation numbers (charges) for the elements in the name.
2) Criss Cross & reduce…. Multiply by the number that will make the charges match
(If charges ALREADY match “multiply by 1” on both!)
Use parenthesis on the polyatomic ion.
3) The number you multiply by IS the subscript in the formula. (NO CHARGES on SUBSCRIPTS.)
(Please remember: a subscript is written smaller than letters & lower than letters on the line.)
Ex1. sodium phosphite
Na3(PO3)1 OR Na3PO3
Na +1
( PO3)-3
+1 x 3 = +3
-3 x 1 = -3
Ex 2. Radium phosphate
Ra3(PO4)2
+2
-3
Ra
+2 x 3 = +6
EX 3. Ammonium phosphide
(NH4)+1
+1 x 3 =+3
notice the formula for phosphate is
completely the same …. we have 2
of the whole thing.
(PO4)
-3 x2 = -6
P -3
-3 x 1 = -3
+
CLASS PRACTICE WRITING POLYATOMIC FORMULAS
Compound Name
Ions & Oxidation # HOW TO SHOW WORK
radium carbonate
cesium nitrite
aluminum sulfate
NOTES PAGE 5
(NH4)3P
Final formula
WRITING FORMULAS OF COMPOUNDS THAT USE ROMAN NUMERALS
KNOW the ROMAN NUMERALS from #1 to #7
1=I
2 = II
3= III
4 = IV
# 4 & #6 are the hardest for students
5= V
6 = VI
7= VII
STEPS TO USE:
1) WRITE the symbols & oxidation numbers (charges) for the elements in the name.
The ROMAN NUMERAL TELLS THE CHARGE ON THE METAL (the first symbol).
2) Criss Cross & reduce…. Multiply by the number that will make the charges match
(If charges ALREADY match “multiply by 1” on both!)
Use parenthesis on the polyatomic ion.
3) The number you multiply by IS the subscript in the formula. (NO CHARGES on SUBSCRIPTS.)
(Please remember: a subscript is written smaller than letters & lower than letters on the line.)
Ex 1. Bismuth III carbonate
EX 2. Plutonium IV sulfide
EX 3. Gold I Sulfite
Bi +3
+3 x 2 = + 6
CO32-
Pu+4
+4 x 2 = + 8
S- 2
Au+1
+1 x 2 = + 1
SO3- 2
Bi2(CO3)3
-2 x 3 = - 6
-2 x 4 = - 8
Pu2S4
reduces to Pu1S2
Au2(SO3)1
-2 x 1 = - 2
a) zirconium IV carbonate
b) Chromium VI chlorate
c) Manganese II phosphide
NAMING BINARY COMPOUNDS—see only 2 symbols!!!
HOW TO NAME
A BINARY COMPOUND
Examples:
LiBr
Formula
1. Name the metal first
2. Then name the nonmetal, with an “ide” ending.
NaCl
Sodium chloride
CaF2
Lithium bromide
Ra3P2
Formula
Name of the Compound
1 Cs3P
3
InF3
2 GaP
4
Ra3N2
NOTES PAGE 6
Calcium fluoride
radium phosphide
NAMING POLYATOMIC COMPOUNDS---see 3 or more symbols!!!
:
Look at the formula symbols and numbers closely.
Is the first symbol part of any of the polyatomic ions in our list?
> IF YES, and it matches, write the name of that ion as the first name.
If this is followed by a nonmetal, write the name of the nonmetal ion ending with –ide.
If it is followed by 2 more symbols… find the second polyatomic ion and write its name AS IS.
> If the first symbol is NOT in any polyatomic ion, look at the remaining symbols,
find the matching ion on the list WITH the proper matching subscripts.
Write the name of the polyatomic ion WITHOUT CHANGE.
Compound
COMPOUND name
Write the formula of the polyatomic
ion, its charge AND write its name
Ex 1. Ba(ClO3)2
(ClO3 ) -1
chlorate
Barium chlorate
Ex 2. Mg3(PO4)2
(PO4)-3
phosphate
Magnesium phosphate
EX 3. NH4Br
(NH4)+1
ammonium
EX 4. (NH4)2SO4
(NH4)+1
AND (SO4)-2
Ammonium bromide
ammonium
Ammonium sulfate
sulfate
1. Sr(ClO2)2
2. Al(ClO4)3
3. NH4Cl
4. NH4ClO3
NOTES PAGE 7
NAMING COMPOUNDS THAT REQUIRE ROMAN NUMERALS
You have already learned that the roman numeral tells the charge on the metal.
If a name said Manganese IV sulfide, YOU KNOW (Mn+4) was used in the compound.
Now that you have used roman numerals in formula writing, learn to identify the roman numeral required
in naming the compound…….
How to know which elements NEED a roman numeral:
If you know the charge of the element when you look at its position on the periodic table, the metal does NOT need
a roman numeral. If you give it a roman numeral anyway…it’s wrong!
If the following image of the periodic table, The BOXED elements do NOT need roman numerals
The “CIRCLED” elements are not even metals and NEVER need a roman numeral EITHER.
How to get a roman numeral……. (Name the ions used…..… then what?)
1. Find the oxidation # (charge) of the SECOND (always negative) ion in the formula. (periodic table is used)
2. MULTIPLY the NEGATIVE CHARGE by the SUBSCRIPT OF THE SECOND ION. = total negative charge
3. The total positive charge EQUALS the total negative charge since the compound is neutral. Write the total positive charge
4. (total positive charge DIVIDED BY the subscript on the first symbol = the roman numeral needed… put it in the name.
Compound
Space to solve for the roman numeral:
HOW TO SHOW YOUR WORK
Name the Compound with the
proper roman numeral
Magnesium… we already KNOW it’s (+2)
NO ROMAN NUMERAL
magnesium sulfide
Ex. PuS2
S-2 (-2) x 2 = (-4) total
Pu (?Charge)
( +4 total ) ÷ 1 = IV
Plutonium IV sulfide
Ex. Pu(ClO2)6
ClO2-1 (-1) x 6 = (-6) total
Pu (?Charge)
Plutonium VI chlorite
Ex.
Mg2S3
CO3-2 (-2) x 1 = (-2) total
Pu (?Charge)
NO ( )’s means 1 !
( +6 total ) ÷ 1 = VI
Ex. PuCO3
Plutonium II chlorite
( +2 total ) ÷ 1 = II
NOTES PAGE 8
How to get a roman numeral…….
US
US2
UPO4
U(ClO3)2
Cu2Se
Cu3P
Cu3PO4
NOTES PAGE 9
MORE CLASS EXAMPLES:
Name the types of elements:
A) Group 1: _______________
E) C, N, O, F, P, S, Cl, Se, Br, I = __________
B) Group 2 _______________
F) Group 17 = ______________
C) Groups 3 to 12: _______________
G) Group 18 = ______________
D) B, Si, Ge, As, Sb, Te, Po = __________
H) Write the oxidation numbers for groups on this periodic table:
I) Draw a line “down” through symbols that do NOT need roman numerals.
NOTES PAGE 10