Lesson 1
Ion Formation
• OBJECTIVES:
–Determine the number of
valence electrons in an
atom of a representative
element.
• OBJECTIVES:
–Describe how cations
form.
• OBJECTIVES:
–Explain how anions form.
Focus Question
Why do elements form compounds?
New Vocabulary
chemical bond
cation
anion
Review Vocabulary
octet rule: atoms tend to gain, lose, or share
electrons in order to acquire eight valence
electrons
Valence Electrons and Chemical Bonds
• A chemical bond is the force that holds two
atoms together.
• Chemical bonds can form by the attraction
between the positive nucleus of one atom
and the negative electrons of another atom,
or by the attraction between positive ions and
negative ions.
Valence Electrons and Chemical Bonds
• Electron-dot structures can be used to
illustrate the formation of chemical bonds.
Valence Electrons and Chemical Bonds
• Ionization energy refers to how easily an atom
loses an electron.
• Electron affinity indicates how much
attraction an atom has for electrons.
• Noble gases, which have high ionization
energies and low electron affinities, show a
general lack of chemical reactivity.
• Noble gases have electron configurations with
a full outermost energy level.
Valence Electrons and Chemical Bonds
• Elements tend to react to acquire the stable
electron structure of a noble gas.
• Atoms try to form an octet—a stable
arrangement of eight valence electrons in the
outer energy level—by gaining or losing
valence electrons.
Positive Ion Formation
• A positive ion forms when an atom loses one
or more valence electrons in order to attain a
noble gas configuration.
• A positively charged ion is called a cation.
Positive Ion Formation
• This figure illustrates
how sodium loses a
valence electron to
become a sodium
cation.
• By losing an
electron, the sodium
atom acquires the
stable outer electron
configuration of
neon.
Positive Ion Formation
• Metals atoms are reactive because they lose
valence electrons easily. Group 1 and 2 metals
are the most reactive metals.
• The ions formed by metal atoms in groups 1,
2, and 13 are summarized below.
Positive Ion Formation
• Transition metals commonly form 2+ or 3+
ions, but can also form ions of 3+ or greater.
• Other relatively stable electron arrangements
are called pseudo-noble gas configurations.
Negative Ion Formation
• Nonmetals easily gain
electrons to attain a
stable outer electron
configuration.
• The figure shows
chlorine gaining an
electron.
• An anion is a negatively
charged ion. Thus, the
chlorine atom becomes
a chloride anion.
Negative Ion Formation
• As shown in the table, nonmetal ions gain
the number of electrons required to fill an
octet and gain a noble-gas configuration.
• Some nonmetals can gain or lose other
numbers of electrons to complete an octet.
Quiz
1. What is true of a chemical bond?
A
It is the force that holds two atoms together.
B
It is never formed by ions.
C
It is formed only by ions.
D
It forms by the attraction between the
positive nucleus of one atom and the
positive nucleus of another atom.
CORRECT
Quiz
2. Which best describes why atoms try to form an
arrangement of eight valence electrons in their outer
energy level?
A
to gain electrons
B
to lose electrons
C
to form ions
D
to acquire the stable electron structure of a CORRECT
noble gas
Quiz
3. Which of the following is true?
A
Anions are positively charged ions.
B
A chloride ion is a cation.
C
A sodium ion is an anion.
D
Cations are positively charge ions.
CORRECT
Quiz
4. Which metals are the most reactive?
A
metals in groups 1 and 3
B
metals in groups 1 and 2
C
metals in groups 2 and 13
D
Metals are not reactive.
CORRECT
Quiz
5. Which letter on the graph represents the zone of
physiological stress?
A
They are not reactive.
B
They all have noble gas configurations.
C
They are found on the left side of the periodic
table.
They easily gain electrons to attain a
CORRECT
stable outer electron configuration.
D