Transcript Atoms and Bonding

Atoms and Bonding - Elements and Atoms
The Building Blocks of Matter
Matter may consist of elements, compounds, or mixtures.
Atoms and Bonding - Elements and Atoms
Atomic Theory and Models
Dalton thought that atoms were like smooth, hard balls that
could not be broken into smaller pieces.
Atoms and Bonding - Elements and Atoms
Atomic Theory and Models
Thomson suggested that atoms had negatively charged
electrons embedded in a positive sphere.
Atoms and Bonding - Elements and Atoms
Atomic Theory and Models
Rutherford was surprised that a few particles were deflected
strongly. This led him to propose an atomic model with a
positively charged nucleus.
Atoms and Bonding - Elements and Atoms
Atomic Theory and Models
Through the first part of the twentieth century, atomic models
continued to change.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
Valence Electrons and Bonding
The number of valence electrons in an atom of an element
determines many properties of that element, including the
ways in which the atom can bond with other atoms.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
The Periodic Table
Elements are organized into rows and columns based on
their atomic number.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
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.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
The Periodic Table
The variety of colors in a “neon” sign
results from passing an electric
current through sealed glass tubes
containing different noble gases.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
Building Vocabulary
After you read the section, reread the paragraphs that
contain definitions of Key Terms. Use the information you
have learned to write a definition of each Key Term in your
own words.
Key Terms:
Examples:
valence
electrons
atomic number
halogen
Valence
electrons
are
that
of
the
The
A
halogen
atomic
isnumber
any element
of electrons
an in
element
Group
is
17,are
the
which
number
consists
of
highest
energy
level
and
are
held
most loosely.
protons
of
elements
in the
with
nucleus
seven
ofvalence
an atom.
electrons.
electron
dot diagram
alkali
metal
period
The
symbol
foristhe
element
surrounded
bywhich
dots that
A
alkali
metal
any
element
in Group 1,
A
row
of
elements
across
the
periodic
table
is called a
stand
forof
valence
electrons
is an
electron
dot
consists
elements
with one
valence
electron.
period.
diagram.
chemical
bond
group
family
A
chemical
is the
force of
that holds
Elements
in bond
the same
column
areattraction
called a group
or
two
atoms together as a result of the rearrangement of
family.
electrons between them.
A
noble
gas isisany
element inbyGroup
18, which
Each
element
represented
a symbol,
usually
consists
of
elements
with
eight
valence
electrons.
consisting of one or two letters.
noble
symbolgas
Atoms and Bonding - Ionic Bonds
Ions and Ionic Bonds
You and a friend walk past a market that sells apples for 40
cents each and pears for 50 cents each. You have 45 cents
and want an apple. Your friend also has 45 cents but wants a
pear.
Atoms and Bonding - 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.
Atoms and Bonding - Ionic Bonds
Ions and Ionic Bonds
Ions are atoms that have lost or
gained electrons.
Atoms and Bonding - Ionic Bonds
Ions and Ionic Bonds
Ionic bonds form as a result of the attraction between
positive and negative ions.
Atoms and Bonding - 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.
Atoms and Bonding - Ionic Bonds
Previewing Visuals
Before you read, preview Figure 17. Then write two
questions that you have about the diagram in a graphic
organizer like the one below. As you read, answer your
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.
Atoms and Bonding - Ionic Bonds
Salt
Click the Video button to watch a movie about salt.
Atoms and Bonding - 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.
Atoms and Bonding - 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.
Atoms and Bonding - 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.
Atoms and Bonding - Covalent Bonds
Comparing Molecular and Ionic Compounds
The table compares the melting
points and boiling points of a few
molecular compounds and ionic
compounds. Use the table to
answer the following questions.
Atoms and Bonding - Covalent Bonds
Comparing Molecular and Ionic Compounds
Graphing:
Create a bar graph of just the
melting points of these
compounds. Arrange the bars in
order of increasing melting point.
The y-axis should start at –
200ºC and go to 900ºC.
Check that the graphs are
correctly set up and labeled
before students plot the data.
Atoms and Bonding - Covalent Bonds
Comparing Molecular and Ionic Compounds
Interpreting Data:
Describe what your graph
reveals about the melting
points of molecular
compounds compared to
those of ionic compounds.
Melting points of molecular
compounds are lower than
those of ionic compounds.
Atoms and Bonding - Covalent Bonds
Comparing Molecular and Ionic Compounds
Inferring:
How can you account for the
differences in melting points
between molecular
compounds and ionic
compounds?
Molecular compounds have
weak attractive force between
molecules, so less energy is
needed to melt molecular
compounds.
Atoms and Bonding - Covalent Bonds
Comparing Molecular and Ionic Compounds
Interpreting Data:
How do the boiling points of
the molecular and ionic
compounds compare?
Boiling points of molecular
compounds are lower than
those of ionic compounds.
Atoms and Bonding - 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.
Atoms and Bonding - 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.
Atoms and Bonding - Covalent Bonds
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a what or how question for
each heading. As you read, write answers to your questions.
Question
Answer
How do covalent bonds form?
Covalent bonds form when two
atoms share electrons.
What are molecular
compounds?
Molecular compounds are
compounds that contain
molecules bonded with covalent
bonds.
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.
Atoms and Bonding - Bonding in Metals
Metallic Bonding
A metal crystal consists of positively
charged metal ions embedded in a
“sea” of valence electrons.
Atoms and Bonding - 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.
Atoms and Bonding - Bonding in Metals
Relating Cause and Effect
As you read, identify the properties of metals that result from
metallic bonding. Write the information in a graphic organizer
like the one below.
Effects
Electrical conductivity
Cause
Metallic bonding
Heat conductivity
Ductility
Malleability
Luster
Atoms and Bonding
Graphic Organizer
Polar
Covalent
Bond
Nonpolar
Covalent
Bond
Metallic
Bond
Equal sharing
of electrons
Attraction
between positive
ions and
surrounding
electrons.
Feature
Ionic Bond
How Bond
Forms
Attraction
between
oppositely
charged ions
Unequal sharing
of electrons
Charge on
Bonded
Atoms?
Yes; positive or
negative
Yes, slightly
positive or slightly No
negative
Yes; positive
Example
NaCl crystal (or
other ionic
compound)
H2O molecule (or
other polar
covalent
molecule)
Calcium (or
other metal)
O2 molecule