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 molecules

1. Draw Lewis dot structure of element (valence e- around symbol)

2. Only draw dots on the four sides (top, bottom, left, right) of the atom

3. 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

anion The 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 –ic The 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…