ATOMS, BONDING, AND THE PERIODIC TABLE
Valence Electrons and Bonding
The number of valence electrons (electrons in the outermost
energy level) in an atom of an element determines many
properties of that element, including the ways in which the
atom can bond with other atoms.
The Periodic Table
As the number of protons (atomic number) increases, the
number of electrons also increases. As a result, the
properties of the elements change in a regular way across a
period.
The maximum # of outermost electrons an atom can
have is eight (even if the energy level could
otherwise hold more).
Question:
Why are noble gases relatively UNreactive?
Question:
Why are noble gases relatively UNreactive?
Their atoms already have eight
outermost electrons, so they are
stable.
Charged Particles
Sometimes an atom can gain or lose electrons
When the # of electrons is different from the #
of protons, then the atom has an electrical
charge.
These atoms are called ions.
- Ionic Bonds
Ions and Ionic Bonds
When an atom loses an electron, it loses a negative charge
and become a positive ion. When an atom gains an electron,
it gains a negative charge and becomes a negative ion.
Ionic Bonds
A bond that forms when one atom takes one or more
electrons from another atom is called an ionic bond.
One atom gains electrons (becomes -); the other atom
loses electrons (becomes +).
The opposite charges (+/-) attract.
Question:
Does a negative ion have more protons or more electrons?
Question:
Does a negative ion have more protons or more electrons?
Answer: More ELECTRONS!
Ionic Bonding with Sodium and
Chlorine
- Ionic Bonds
Ions and Ionic Bonds
Ionic bonds form as a result of the attraction between
positive and negative ions.
- Ionic Bonds
Properties of Ionic Compounds
In general, ionic compounds are hard, brittle crystals that
have high melting points. When dissolved in water or melted,
they conduct electricity.
Nomenclature
We write ions with their chemical symbol, then with a +
or – the number of electrons lost or gained.
A “+” charge indicates the # of electrons lost
A “-” charge indicates the # of electrons gained.
- Ionic Bonds
Ions and Ionic Bonds
Ions are atoms that have lost or
gained electrons.
- Ionic Bonds
Check Questions
Formation of an Ionic Bond
Q. What is an ionic bond?
A. An ionic bond is the attraction between two oppositely charged ions.
Q. What is the overall charge on an ionic compound?
A. Overall, an ionic compound is electrically neutral.
End of Section:
Ionic Bonds
"My name is Bond… Covalent Bond."
Covalent Bonding
Covalent Bonding
A bond formed when atoms share electrons
Let’s fill in the blanks:
An atom wants to fill its outermost energy level
with _______ electrons, unless they are the
elements _________ or ________, which only
want ____.
Covalent Bonding
A bond formed when atoms share electrons
Let’s fill in the blanks:
An atom wants to fill its outermost energy level
with _eight__ electrons, unless they are the
elements _________ or ________, which only
want ____.
Covalent Bonding
A bond formed when atoms share electrons
Let’s fill in the blanks:
An atom wants to fill its outermost energy level
with _eight__ electrons, unless they are the
elements _Hydrogen_ or _Helium_, which only
want ____.
Covalent Bonding
A bond formed when atoms share electrons
Let’s fill in the blanks:
An atom wants to fill its outermost energy level
with _eight__ electrons, unless they are the
elements _Hydrogen_ or _Helium_, which only
want two_.
- Covalent Bonds
How Covalent Bonds Form
The force that holds atoms together in a covalent bond is the
attraction of each atom’s nucleus for the shared pair of
electrons.
- Covalent Bonds
How Covalent Bonds Form
The oxygen atom in water and the nitrogen atom in ammonia
are each surrounded by eight electrons as a result of sharing
electrons with hydrogen atoms.
- Covalent Bonds
How Covalent Bonds Form
An oxygen molecule contains one double bond, while a
carbon dioxide molecule has two double bonds. A nitrogen
molecule contains one triple bond.
- Covalent Bonds
Unequal Sharing of Electrons
Fluorine forms a nonpolar bond with another fluorine atom. In
hydrogen fluoride, fluorine attracts electrons more strongly
than hydrogen does, so the bond formed is polar.
- Covalent Bonds
Unequal Sharing of Electrons
A carbon dioxide molecule is a nonpolar molecule because
of its straight-line shape. In contrast, a water molecule is a
polar molecule because of its bent shape.
- Covalent Bonds
Asking Questions
Question
Answer
How do covalent bonds form?
Covalent bonds form when two
atoms share electrons.
How does unequal sharing of
electrons affect the atoms in
molecular compounds?
Unequal sharing of electrons
causes the bonded atoms to
have slight electrical charges.
End of Section:
Covalent Bonds
- Bonding in Metals
Metallic Bonding
A metal crystal consists of positively
charged metal ions embedded in a
“sea” of valence electrons.
- Bonding in Metals
Metallic Properties
The “sea of electrons”
model of solid metals
explains their ability to
conduct heat and
electricity, the ease with
which they can be made
to change shape, and
their luster.
- Bonding in Metals
Properties of Metals due to Metallic Bonding
Effects
Electrical conductivity
Cause
Metallic bonding
Heat conductivity
Ductility
Malleability
Luster
End of Section:
Bonding in
Metals
Graphic Organizer
Polar
Covalent
Bond
Feature
Ionic Bond
How Bond
Forms
Attraction
between opposite Unequal sharing
of electrons
(+/-) ions
Charge on
Bonded
Atoms?
Yes; positive or
negative
Example
Na+Cl-
Nonpolar
Covalent
Bond
Metallic
Bond
Equal sharing
of electrons
Attraction
between positive
ions and “sea” of
electrons.
Yes, slightly
positive or slightly No
negative
H2O
O2
Yes; positive
because the
electrons are only
loosely connected
Gold