Atoms and Molecules
Basic units of EVERYTHING!
Which of these is true?
1. “Atom” and
“molecule” mean
the same thing.
2. Atoms are made of
molecules.
3. Molecules are
made of atoms.
82%
15%
3%
1
2
3
What is the smallest structure in this list that can be
seen with an ordinary desk microscope?
1.
2.
3.
4.
Cells.
Cell nucleus.
Atoms.
Chain molecules,
such as proteins.
35%
38%
18%
10%
1
2
3
4
Atoms
In our model of scale, remember that
the BB represented an atom.
Electrons
Hydrogen
Helium
Neutrons
Protons
As a class, identify the atoms represented here and label
the sub-atomic particles.
Carbon
Oxygen Phosphorous
Calcium
What elements are represented here? Use the Periodic
Table on the wall to identify these atoms.
What does the term “valence shell” mean? Label the
valence shell on each of these.
Ions
Loss or gain of
an electron
makes an atom
into an ion.
-
+
Gaining an electron
makes a positive or
negative ion?
-
Losing an electron
makes a positive
or negative ion?
Isotopes
Atoms that gain or lose a
neutron become isotopes.
Radioactive isotopes are
used in medicine for
imaging (such as PET
scanners).
Why is this important?
• Each element has distinct properties:
color, melting point, reactivity, etc.
• The basic atomic structure of each
element determines that element’s
properties. Change the structure, and
you have an entirely different element.
Which of these is found in the
nucleus of an atom?
78%
1.
2.
3.
4.
Protons
Electrons
DNA
Depends on the
atom
11%
6%
1
2
3
6%
4
An ion is an atom that has lost
or gained:
83%
1.
2.
3.
4.
An electron
A proton
A neutron
Any sub-atomic
particle
6%
1
2
11%
0%
3
4
T or F: An atomic nucleus and a cell
nucleus are about the same size.
33%
33%
33%
1. True
2. False
3. Depends on which
cell and which atom.
1
2
3
Atoms bond together
• Molecules are made up of atoms bonded
together.
• The structure of an individual atom
determines:
• Whether the atom can form bonds.
• How many other atoms it can bond to.
In our model of scale, remember that
the marble represented a small
molecule, such as glucose.
How many atoms
can each of these
atoms bond with?
How do we know?
1
4
3
2
5
2
Fill in the blank column with number of covalent bonds
formed by each atom.
Ionic Bonding
Ionic substances tend to form crystaline lattices
rather than distinct molecules.
Covalent Bonding
Co = together
valent = valence
shells
The hydrogen atom. How many bonds can it form?
Covalent bonding
A hydrogen
molecule. How
many
hydrogen
atoms are
involved? Can
there be
more? Why or
why not?
W
O
R
K
• Describe in your own words the
difference between ionic and covalent
bonding.
T
O
G
E
T
H
E
R
Covalent Bonding
Polar bonding between atoms produces a polar
molecule, which has areas with slightly positive or
slightly negative charges.
W
O
R
K
• Describe in your own words the
difference between nonpolar and polar
covalent bonding
T
O
G
E
T
H
E
R
When atoms bond together,
they make:
20%
1.
2.
3.
4.
5.
20%
20%
2
3
20%
20%
Cells
Molecules
More atoms
Ions
Isotopes
1
4
5
Which of these is true?
1. Molecules and cells
are about the same
size.
2. Molecules are much
smaller than cells.
3. Cells are much smaller
than molecules.
4. “Cell” and “molecule”
mean the same thing.
94%
6%
0%
1
2
3
0%
4
Which kind of bond between atoms
creates a distinct molecule?
44%
1. Ionic bonding
2. Covalent bonding
3. Both ionic and
covalent bonding.
39%
17%
1
2
3
Which is true about polar
covalent bonding?
1. An electron is shared
equally between two
atoms.
2. An electron is shared
unequally between
two atoms.
3. An electron leaves
one atoms and
becomes part of
another.
94%
6%
1
0%
2
3
True or false? The atomic “shell” is a cell
membrane.
88%
1. True
2. False
13%
1
2
Why is polarity so important?
Salt dissolves in water.
Oil does not.
Why?
What will oil dissolve in? Why?
• Is a water molecule in the gas phase
larger than, smaller than, or the same
size as a water molecule in the solid
phase?
• Describe what happens to water
molecules as liquid water evaporates.
W
O
R
K
T
O
G
E
T
H
E
R
Molecules bond together
Weak attractive forces between
molecules are called hydrogen
bonds.
Here, sugar (a polar substance) is in solution
with water (also polar). Mark where the
hydrogen bonds will form.
Hydrogen bonding occurs:
25%
25%
25%
25%
1. Between atoms.
2. Between
molecules.
3. Between cells
4. Between any
particles.
1
2
3
4
Hydrogen bonding is:
1. Strong and difficult
to break, like polar
covalent bonding.
2. A strong attraction
between charged
ions, like ionic
bonding.
3. A weak attraction
between polar
molecules.
33%
1
33%
2
33%
3
Properties of Water
• Water is:
• Cohesive
• Adhesive
• A “universal solvent”
• Water also has:
• A high specific heat
• A high heat of vaporization
pH is a ratio between H+ and OH- ions in solution.
• One unusual property of water is that it is
less dense in the solid stage than in the
liquid stage, which causes ice to float.
Why does water become less dense as it
freezes? Use what you learned about
hydrogen bonding between molecules.
W
O
R
K
T
O
G
E
T
H
E
R
Recap
1. What is the difference between atoms
and molecules?
2. What is the difference between ionic
bonding and polar covalent bonding?
3. How is polarity related to pH?