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Chapter 20
Chemical Bonds
Physical Science
Chemical Bonds
 Answer In your Notes!!
 What do you think a chemical bond is?
 What does it consist of?
Chemical Bonds
 Chemical bond  forces holding atoms
together to form molecules and solids
 The attraction is between e- of one atom
to the nucleus of another atom
 Electric in nature
Section 1
Stability in Bonding
Combined Elements
Uncombined elements such as copper, sulfur
and oxygen can chemically combine to
form a compound when conditions are
right
EX: Statue of Liberty coloring
Section 1
Combined Elements
When elements combine, the new compound has
unique properties
EX: Na + Cl = NaCl (table salt)
Sodium is a soft, shiny metal that reacts violently
w/ water
Chlorine is a poisonous greenish-yellow gas
Section 1
Formulas
Chemical formula- shows elements a compound
contains and the exact number of atoms of each
element
Chemical symbols & numbers are shorthand for the
elements and their amounts in a chemical
formula
EX: H20 contains:

2 hydrogen atoms & 1 oxygen atom
Formula
Examples
 H2SO4
 How many hydrogen atoms are there?
 How many sulfur atoms are there?
 How many oxygen atoms are there?
 SiO2
 How many silicon atoms are there?
 How many oxygen atoms are there?
Review Questions
1.Describe what a chemical formula tell you.
2.Describe how the properties of table salt (NaCl)
are different from those of sodium (Na) and
chlorine (Cl).
Noble Gases
To understand the stability of the
noble gases, it is helpful to look
at electron dot diagrams
Electron dot diagrams show only
the electrons in the outer energy
level of an atom
Notice that eight dots surround Kr, Ne, Xe, Ar, and
Rn, and two dots surround He.
Outer Levels-Getting Their Fill
How do elements, trying to become stable, gain or
lose its outer electrons?
Elements gain, lose, or share electrons to become
stable by combining with other atoms that also
have partially complete outer energy levels
Electron dot diagrams
for sodium and chlorine.
Outer Levels-Getting Their Fill
•Fewer than 4 e-  give up e*More than 4 e-  gain e-
*4 e-  will try to share e- with
another element
*Want 8 e- in the outer shell!
Stability is Reached
When atoms gain, lose, or share electrons, an
attraction forms between the atoms, pulling
them together to form a compound
This attraction is called a chemical bond
Bellwork
1.
Why do elements form compounds?
2. What is a chemical bond?
3. Why are Noble Gases stable?
4. List the 3 ways bonds can be formed.
Write in your notes
Answers
 To become more chemically stable by getting a
complete outer energy level
 The force that holds atoms together in a
compound
 Because they have a full outer energy level
 Electrons are gained, lost or shared
Section 2 Types of Bonds
Gain or Loss of Electrons
1. An atom that has lost or gained electrons is
called an ion.
2. An ion is a charged particle
What do you think happens to the charge of an
atom if it loses an electron?
What do you think happens to the charge of an
atom if it gains an electron?
Section 2 Types of Bonds
Gain or Loss of Electrons
1.
Atom loses an electron, it becomes + ion.
a superscript indicates the charge
1.
Atom gains an electron it becomes a − ion.
Section 2 Types of Bonds
A Bond Forms
A neutral atom of potassium has one electron in its outer
level.
Is this a stable outer energy level? Why or Why not?
When potassium forms a compound with iodine, potassium
_____ one electron in it’s fourth level.
What happens to the third level?
Section 2 Types of Bonds
A Bond Forms
 The potassium atom has become an ion.
 When a potassium atom loses an electron, the atom
becomes positively charged because there is one
electron less in the atom than there are protons in the
nucleus
 The 1+ charge is shown as what?
Section 2 Types of Bonds
A Bond Forms
 The iodine atom in this reaction undergoes change, as
well.
 During the reaction with potassium, the iodide atom
gains an electron, leaving its outer energy level with
eight electrons. Is this considered stable?
 This atom is no longer neutral because it gained an
extra negative particle.
 It now has a charge of 1 −
Section 2 Types of Bonds
A Bond Forms
 The resulting compound has a neutral charge because
the positive and negative charges of the ions cancel
each other.
Section 2 Types of Bonds
Ionic Bond
 Ionic bond- the force of attraction between
opposite charges of the ions
 In an ionic bond, a transfer of electrons takes place
 If an element loses electrons, one or more elements
must gain an equal number of electrons to maintain the
neutral charge of the compound
 Remember….
An ionic bond is usually formed between a ____ & ____
------ANSWER: METAL AND NONMETAL
Section 2 Types of Bonds
Ionic Bond
Notice that Mg is losing 2 electrons and each of the Cl
atoms is gaining 1 electron
What is lost is equally gained, therefore, the sum of
the charges on the ions is zero
Section 2 Types of Bonds
Sharing Electrons
 For example, the elements in Group 14 of the periodic
table have four electrons in their outer levels.
 These atoms become more chemically stable by sharing
electrons, rather than by losing or gaining electrons.
Section 2 Types of Bonds
Covalent Bonds
 The attraction that forms between atoms when they
share electrons is known as a covalent bond
 A neutral particle that forms as a result of electron
sharing is called a molecule
 Atoms can form double and triple bonds depending on
whether they share two or three pairs of electrons
Section 2 Types of Bonds
Polar or Nonpolar
• A polar molecule has a slightly positive end and a
slightly negative end, molecule is neutral. Water is an
example of a polar molecule.
• A nonpolar molecule is one in which electrons are
shared equally in bonds.
Section 2 Discussion Questions
Write in your notes to help you study for the quiz!!
 What is the sum of the charges when a compound is
neutral?
 Can atoms become more stable by sharing electrons?
 A neutral particle that forms as a result of electron
sharing is called a ________.
 A single covalent bond is made up of how many
electrons?
Answers
 1). Zero (p. 610)
 2). Yes ( p. 611)
 3). molecule ( p. 611)
 4). 2 shared electrons ( p. 611)
Section 3 Writing Formulas and
Naming Compounds
A.
Chemists use symbols from the periodic table to write
formulas for compounds
B.
Binary compound - compound composed of two
elements
NOTE: Before you can write a formula, you need to know
what the elements are and what number of electrons
they GAIN, LOSE, or SHARE to be come stable.
Oxidation Numbers
 Oxidation number- how many electrons an atom has
gained, lost, or shared to become stable
 In ionic compounds the oxidation number is the same as
the charge of the ion
 Elements can have more than one oxidation number
Determining Neutral Compounds
 When writing a formula it is important to know that the
compound is neutral (even thought the individual ions
carry a charge)
 The formula must have the right # of +ions and the right
# of –ions so the charges balance
 Use oxidation numbers or their least common multiples
to write formulas
 Use the name of the first element, the root name if the
second element, and the suffix -ide to write the name
of a binary compound
Examples of Neutral Compounds
EXAMPLE 1:
NaCl (sodium chloride)
Sodium ion has a 1+ charge
Chlorine ion has a 1- charge
One of each ion makes this compound neutral
Examples of Neutral Compounds
EXAMPLE 2:
CaF (calcium flouride)
Calcium ion has a 2+ charge
Flourine ion has a 1- charge
In this case you need to have 2 flourine ions for every
calcium ion in order for the charges to cancel and the
compound to be neutral.
Neutral formula = CaF2
Examples of Neutral Compounds
Example 3:
AlO3 (Aluminum oxide)
Aluminum ion has a charge of 3+
Oxygen ion has a charge of 2Here you need to determine the least common multiple of
3 and 2 in order to determine how many ions of each
you need. 6 is the least common multiple of these two
numbers.
You will need 2 aluminums and 3 oxygen ions to have a 6+
charge and a 6- charge for a neutral compound
Neutral compound = Al2O3
Steps of Writing Formulas
1. Write the symbol of the element or polyatomic ion
(ions containing more than one atom) that has the
positive oxidation number.
2. Write the symbol of the element or polyatomic ion
with the negative oxidation number.
3. The charge (without the sign) of one ion becomes the
subscript of the other ion. Reduce the subscripts to
the smallest whole numbers that retain the ratio of
ions.
Steps of Writing Names
for Binary Ionic Compounds
1. Write the name of the positive ion.
2. Check to see if the positive ion is
capable of forming more than one
oxidation number.
3. Write the charge of the positive ion
using roman numerals in parentheses
after the ion’s name if it has more than one oxidation
number.
Steps to Writing Names
for Binary Ionic Compounds
1. Write the whole first name of the first element.
2. Write the ‘root’ of the second element.
3. Add –ide or –ate.
4. Ex: Li Br
5. Lithium Bromide
Compounds with Added Water
 Some ionic compounds have water molecules as part of
their structure. These compounds are called hydrates.
 A hydrate is a compound that has water chemically
attached to its ions and written into its chemical
formula.
 When writing a formula that contains a hydrate, the
number is shown after a “”. Following the number 2
is the formula for water as shown.
Steps for Naming
Binary Covalent Compounds
 Some pairs of nonmetals can form more than
one compound with each other.
 Prefixes are used to indicate how
many atoms of each element are in a
binary covalent compound.
 The last vowel of the prefix is
dropped when the second element begins
with a vowel as in pentoxide.
KNOW THESE PREFIXES
Using Prefixes
 These same prefixes are used when naming the
hydrates previously discussed.
 The main ionic compound is named the regular way,
but the number of water molecules in the hydrate is
indicated by the Greek prefix.
Questions
 A binary compound is composed of two _____.
 The net charge of a compound is ______.
 A _______ is a compound that has water attached to its
ions.
 What prefix would be used for 7 atoms of one element
in a covalent bond?
 What is the 1st step in writing the formula for a binary
ionic or binary compound formula?