Nomenclature and Chemical Bonding
Be sure you memorize the list of polyatomic ions that you have been provided.
Ionic is the TRANSFER OF ELECTRONS
Ionic- Metal & a NON-METAL
REMINDER
Covalent (co—sharing; valent—outermost shell) when electrons are shared between 2
nuclei
Molecule- a group of atoms held together by covalent bonds
In covalent bonding, the atoms are able to achieve an octet through the sharing of electrons
Covalent bonds
Are held together by the attraction of electrons of one atom and the nucleus of a second atom
Their bonds are flexible, somewhat like springs
A single bond forms from a single pair of shared electrons
Molecules
Br Br Br-Br
Molecular compound names include prefixes that indicate the number of atoms in the molecule
They are composed of nonmetal elements
Naming Binary Covalent compounds
Write the name of the least electronegative element with a prefix to indicate the number of atoms of the element that are present
Prefix mono- is NOT written with the first word of a covalent compound’s name
Write the name of the most electronegative element second with a prefix to indicate the number of atoms of the element that are present
Naming Binary Covalent compounds
# of atoms
Prefix # of atoms
Prefix
1 Mono- 6 Hexa-
2 Di- 7 Hepta-
3 Tri- 8 Octa-
4 Tetra- 9 Nona-
5 Penta- 10 Deca-
Some prefixes are sometimes shortened to make a name easier to say (aka: you may have to remove the “a”)
Suffix –ide is added to the name of the last element
Examples: CCl4 – carbon tetrachloride NO- nitrogen monoxide
Naming covalent compounds
1. What are the differences between ionic and covalent bonds?
2. Name the following covalent compounds:a) S2O3
b) CO2
c) PBr5
Your Ticket Out The Door
Atoms bond to obtain a full set of 8 valence electrons (octet rule) Lose or gain e- (ionic bonded) Sharing e- (covalent bond)
Molecule – 2 or more atoms bond covalently, usually nonmetals
DIATOMIC MOLECULES (Be able to write 7 diatomic elements with correct formulas – hint: the elements form a 7 plus H2)H2, N2, O2, F2, Cl2, Br2, I2
LEWIS DOT
Lewis dot structures: use e- dot diagram to show how electrons are arranged in molecules1. Draw Lewis dot structure of element (valence e- around symbol)2. Only draw dots on the four sides (top, bottom, left, right) of the
atom3. Connect only single dots
Lone pair e- help shape molecules by pushing other atoms down
LEWIS DOT
How many e- are shared by the groups? Group 14 shares 4 e- Group 15 shares 3 e- Group 16 shares 2 e- Group 17 and H share 1 e-
Single covalent bonds are also called sigma bonds (σ)
Covalent compounds can also have double bonds (each shares 2 e-)
Covalent compounds can have triple bonds (each shares
LEWIS DOT
2 PAIRS of shared electrons form a double bond
This is 1 DOUBLE BOND
Double Bond
O OC
So, what would a triple bond look like? Each line represents 1 shared PAIR of electrons
Triple Bond
N NIs there something unusual here?
H2
CH4
NH3
H2O
TRY THESE…
Lower melting and boiling points vs. ionic
Molecules have no charge, hence do not conduct heat or electricity in any state.
Melting molecular compounds Does NOT separate the clusters of atoms within a molecule,
Separates just molecules from each other
Covalent Compound Properties
An acid is a molecular substance that dissolves in water to produce hydrogen ions NOTE: ALL acids contain hydrogen… BUT…
Not everything with hydrogen is an acid!They are covalent compounds that separate into a cation and an anion in water (ionic tendency)
What is an acid?
Binary acids:The name begins with the prefix
hydro-The name is derived from the anionThe suffix –ide should be changed
to –ic
Naming Acids
One of the many uses for HCl is cleaning concrete, but it’s also found in your stomach…What is the name of this acid?
Some wheel cleaning compounds used in carwashes contain hydrofluoric acid. What is the formula for this acid?
Try two for yourself…
Polyatomic acids:Do not use prefix hydro-The suffix –ate should be changed
to –icThe suffix –ite should be changed
to –ous
Naming Acids
In addition to its many other uses, nitric acid is commonly used in the woodworking industry to artificially age pine and maple. What is the formula for this acid?
What would be the name of HClO2
H2CrO4 was once widely used in the band instrument repair industry, because of its ability to “birghten” raw brass. What is the name of this acid?
Don’t worry, these problems won’t corrode your brain…
Use prefixes
Binary compound
Metal present
yes
no yes
Does the metal form more than one cation?
Use elementname
Use element name with proper Roman numeral
no
Polyatomic ionor ions present?
yes
Use the polyatomicname as appropriate
no yes
no
Not established
no no
yes yesUse Acid naming
rules
Is hydrogen the cation?
Is hydrogen the cation?
Naming AcidsIs oxygen in the anion
yes no
Hydro-+ anion root+ -icHydro(anion root)ic acid
anion or element root+ -ous(root)ous acid
anion or element root+ -ic(root)ic acid
Check the ending of the anion name
-ite -ate
A diatomic molecule is a molecule formed from two identical atoms
The atoms join together because they are more stable that way than if they exist as single atoms
Remember HOFBrINCl H2, O2, F2, Br2, I2, N2, and Cl2
Diatomic Elements
Not KNOWING the 14 polyatomics – correct formula and charges
Not KNOWING the charges of elements based on the periodic table. Alkali metals are 1+, alkaline earth metals are 2+,
aluminum is 3+, nitrogen group is 3-, oxygen group is 2-, halogens are 1-.
Transition metals (except zinc, cadmium, and silver) and metals in the P block have more than 1 charge.
Not putting the parentheses around hydroxide when there is more than 1. OH2 is water; (OH)2 is 2 hydroxides
Not simplifying (if the charges are the same, no subscripts are needed)
Not using roman numerals correctly in the names.
Common Mistakes…