ionic bonding. pure substances & nomenclature pure substances can exist in several forms: i)...
TRANSCRIPT
Unit 5Ionic Bonding
Pure Substances & NomenclaturePure substances can exist in several forms: I)
Atomic Elements & Molecular Elements, II) Ionic Compounds and III) Molecular Compounds (studied in next unit)
I. - Atomic Elements & Molecular Elements: Some elements can exist as single atoms such as He, Ne, Cu, Hg, Au, Pb, U- Molecular Elements: Some elements exist in nature as diatomic molecules: H2 N2 O2 F2 Cl2 Br2 I2
Know theseTheir names are the same as the element
names
Two elements are commonly polyatomic. Sulfur S8
Phosphorous P4
II. Ionic Compounds
II. Ionic Compounds: These are compounds formed between ions. The metal loses electrons to become a + ion
(Cation), and the nonmetal gains electrons to become a – ion (Anion).
The + and – ions are attracted to each other in a ratio so that the resulting compound is neutral in charge; NaCl MgF2 are examples.
The formula unit is the simplest ratio of ionsThese have unique names formed from
naming the + ion followed by the – ion with an “ide” ending.
“Perhaps one of you gentlemen would mind telling me just what is outside the window that you find so attractive..?”
Image courtesy NearingZero.net
Valence electrons
Are electrons in highest occupied energy level of an atom.
For representative elements, number of valence electrons is the same as its group number.Ex. Lithium is in group 1A: has 1 valence
electronSome transition metals form more than one
ion.Ex. Fe2+ and Fe3+
Octet rule: atoms tend to achieve the electron configuration of a noble gas (8 electrons in outer energy level)by gaining or losing electrons.
elements of Group 2A have a
+2 charge
elements of Group 5A have a
-3 charge
elements of Group 6A have a
-2 charge
elements of Group 7A have a
-1 charge
The charge on an ion can be predicted from its position in the periodic table.
Elements in Group 1A have a +1 charge
→
remove e-
neutral atom cation
If one or more electrons are removed from a neutral atom a positive ion is formed. A positive ion is called a cation.
Atom sodium (Na)
calcium (Ca)
lithium (Li) strontium (Sr)
Cation Na+ Ca+2 Li+ Sr+2
Name of Cation
Sodium ion
calcium ion
Lithium ion
strontium ion
Naming Cations
Cations are named the same as their parent atoms.
If one or more electrons are added to a neutral atom a negative ion is formed. A negative ion is called an anion.
→neutral atom
add e-
anion
An anion consisting of one element has the stem of the parent element and an –ide ending
Naming Anions
Atom
Anion
Name of Anion
fluorine (F)
F-
fluoride ion
stem
Atom
Anion
Name of Anion
chlorine (Cl)
Cl-
Chloride ion
stem
Atom
Anion
Name of Anion
bromine (Br)
Br-
bromide ion
stem
Atom
Anion
Name of Anion
nitrogen (N)
N3
-
nitride ion
stem
Atom
Anion
Name of Anion
phosphorous (P)
P3
-
phosphide ion
stem
Atom
Anion
Name of Anion
oxygen (O)
O2-
oxide ion
stem
A chemical compound must have anet charge of zero.
Writing Formulas FromNames of Ionic Compounds
If the compound contains ions, then the charges on all of the ions must add to zero.
Example: Aluminum ChlorideStep 1:
Step 2:
Step 3: 1 3
Step 4: AlCl3
Criss-Cross Method
Al Cl
Al Cl
3+ 1-
write out name with space
write symbols & value of charge of ions
criss-cross charges as subsrcipts
combine as formula unit(“1” is never shown)
Aluminum Chloride
Example: Aluminum OxideStep 1: Aluminum Oxide
Step 2: Al3+ O2-
Step 3: Al O2 3
Step 4: Al2O3
Criss-Cross Rule
Example: Magnesium OxideStep 1: Magnesium Oxide
Step 2: Mg2+ O2-
Step 3: Mg O
2 2
Step 4: Mg2O2
Step 5: MgO
Criss-Cross Rule
Use simplest ratios
Naming ionic compounds
To name an ionic compound first write the name of the cation (+ ion) followed by the name of the anion (- ion)
Naming Binary CompoundsFormula Name
1 BaO ____________________
2 ________________ sodium bromide
3 MgI2 ____________________
4 KCl ____________________
5 ________________ strontium fluoride
6 ________________ cesium fluoride
barium oxide
NaBr
magnesium iodide
potassium chloride
SrF2
CsF
Classwork: handout ionic binary compounds (single charge cations.)
A polyatomic ion is an ion that contains two or more elements.
-3NO
Naming Compounds Containing Polyatomic Ions
Al2(SO4 )3
subscripts
superscripts
ALUMINUM SULFATE
SO42- Al3+
Rules for ParenthesesParentheses are used only when the following two condition are met:
1. There is a polyatomic ion present and…2. There are two or more polyatomic ions in the formula.
Examples:
NaNO3 NO31- is a polyatomic ion, but there is only one of it.
Co(NO3)2 NO31- is a polyatomic ion and there are two of them
(NH4)2SO4 NH41+ is a polyatomic ion and there are two of them;
SO42- is a polyatomic ion but there is only one of it.