Chemical Bonding
Chapter 13
A compound is a new substance formed when two or more elements “combine chemically”.
ex. water H2O
sugar C6H12O6
A chemical formula is a symbol name for a compound.
ex. CO2 - carbon dioxide
Advantages of using formulas
1. lists the elements present.
2. gives the “recipe” or the ratio for the compound.
A subscript is a number written to the lower right of the symbol to indicate how many atoms of the element are used.
ex. H2O the 2 is a
subscript.
If no subscript is shown, the symbol represents one atom of the element is present.
Bonding is the process of joining atoms chemically.
Atoms will join together to make compounds in order to become chemically stable.
An atom is considered to be chemically stable if its outer energy level is full or has at least 8 electrons in it.
Types of bonding
1. Ionic Bonding
· Occurs between a metal and a nonmetal.
· Metal atoms give electrons to nonmetal atoms to have stable outer energy levels.
· Ionic bonding is known as “electron transfer”.
Atoms with electrical charge are called ions. An ion either lost or gained an electron.
The positive charge of the metal ion attracts the negative charge of the nonmetal ion to hold the atoms together in the compound.
“opposite charges attract”
(make drawing of Ionic Bond here)
In an ionic compound formula, the metal is always listed first.
Characteristics of ionic compounds
1. crystal shape
2. high melting points
3. electrical conductivity –when dissolved in water ions separate and move freely conducting electricity.
2. Covalent Bonding
· Occurs between nonmetal atoms only
· Atoms share electrons in their outer energy levels in order to be chemically stable.
· Covalent bonding is known as “electron sharing.”
(make drawing of Covalent Bond here)
Atoms that are sharing electrons form molecules.
A molecule is the smallest part of a covalent compound.
Diatomic elements are elements whose atoms form 2 atom molecules
ex. H2 , N2 , O2 , F2 , Cl2,
I2 , Br2
A polar molecule has a positive and a negative end (unequal sharing of electrons between atoms).
ex. H2O water
HCl hydrochloric
acid
The oxidation number is the number of electrons lost, gained, or shared by an atom.
· It is written to the upper right of the symbol.
+ positive numbers mean electrons are lost by the atom.
ex. Na1+ means sodium
loses one electron.
- negative numbers mean electrons are gained by the atom.
ex. Cl1- means chlorine
takes or gains one electron.
The elements in a family usually have the same oxidation number (check their group #).
A binary compound is composed of two elements.
Rules for writing binary compound formulas
1. List the element symbols with the metal first.
2. List the oxidation number.
3. Use the diagonal rule if the oxidation numbers are different.
Rules for Naming Binary Compounds
1. Write the name of the first element.
2. Write the root for the second element and add the –ide ending.
ex. NaCl
Sodium chloride
root ending
The Transition Elements (groups 3-12) are metals that have multiple (more than one) oxidation numbers.
The oxidation number for a transition element is indicated by a Roman Numeral written in parenthesis beside the element name.
Examples:
Copper(II) = Cu 2+
Iron(II) = Fe 2+
Iron(III) = Fe 3+
To write a formula for
Iron(III) & oxygen:
Fe3+ O2-
When naming binary compounds containing a transition element, a roman numeral must be listed after the metal.
Examples: FeCl3
Iron(III) chloride
AgBr
Silver(I) bromide
Cu3P2
Copper(II) phosphide
A polyatomic ion is an electrically charged group of atoms held together by covalent bonding that acts like one single charged atom.
ex. Hydroxide
(OH1-)
To write formulas containing polyatomic ions follow the rules for binary compounds. If more than one of that ion is needed write parenthesis around the group before adding the subscript.
example:
Calcium hydroxide
Ca2+ (OH1-)
Ca2+ (OH1-)
Ca (OH)2
2