Download Unit 2: All Biology is Chemistry

Unit 2:
All Biology is
Chemistry
Lesson 2: The Chemistry of Life
O
V
C
Se
N
H
Drill
11 October 2011
Look at the chemical symbols to the left.
1. Name each element.
2. Which element is most abundant in the
human body? Least abundant?
3. Which element(s) are major elements for
the human body?
4. Be prepared to share information
about the trace element you
researched for homework.
Objectives
At the conclusion of this lesson students will be
able to:
4. Explain the relationship between elements and
atoms.
5. Identify and compare the charge, mass, and
location of subatomic particles.
6. Draw and label a Bohr model of the structure
of the atom.
7. Be able to calculate the mass number of an
atom.
8. Define isotope and explain two of their uses in
biology.
The Atom –
The Simplest of Particles
• The atom is the simplest particle of an
element that retains the properties of
that element.
– From Greek word “atomos” meaning
“unable to be cut.”
Obj. 1
The Structure of an Atom
Bohr Model – “planetary model”
• Proposed by Niels Bohr in 1915
• A useful approximation of the structure
of an atom.
Consists of two parts:
• A central region, or nucleus
• Electron cloud – composed of orbitals
or three-dimensional regions around a
nucleus
The Bohr Model
Below is a Bohr Model of a helium (He) atom.
Nucleus
2 protons
2 neutrons
n +
+ n
Electron cloud
Consists of orbitals
where high-energy
electrons orbit the
nucleus
Subatomic Particles
Protons
Positively (+) charged particles
Have mass (1 amu = 1 atomic mass unit)
Located in the nucleus
Neutrons
Neutral particles (No charge)
Have mass – 1 amu
Also located in the nucleus
Obj. 3
Electrons
Negatively (-) charged particles
Mass is negligible (1/1840 amu)
Remain in constant motion in orbitals
+
n
Another Look at the Periodic Table
Atomic Number
6
C
12.011
Atomically Speaking…
• The number of protons in an atom is called
the atomic number.
• In an atom, the number of positive protons is
balanced by an equal number of negative
electrons.
– net electrical charge equals zero
The Bohr model to the left represents
an atom of which element?
How many electrons must be in the
electron cloud?
= neutron
= proton
Atomically Speaking…
• The mass number of an atom is equal
to the total number of protons and
neutrons of the atom.
What is the mass number of our
carbon atom?
= neutron
Obj. 4
= proton
Isotope:
Isotopes:
from the
Greek isos,
meaning
“equal” and
topos,
meaning
“place”
Not All Atoms are Created Equal
Isotopes are atoms of the same element that have
different numbers of neutrons.
– therefore they will have different mass numbers
– this is the reason for the average atomic mass in the
periodic table
Click here to compare
these
twoare
atoms.
These two
atoms
both
carbon atoms. But the atom on
the left has 6 neutrons while the
atom on the right has 7 neutrons.
Because of this, these two atoms
are said to be isotopes of one
another.
CLOSE
Obj. 5
= neutron
= proton
Radioactive Isotopes
• Sometimes having too many neutrons can
make the nucleus of an atom unstable.
– Unstable nuclei decay, or break apart.
– Particles (usually neutrons) and energy in the
form of radiation are released.
– This radiation can be used to
calculate the age of an object or it
can be used in medical treatments
such as radiation therapy.
A Few Words About Electrons
• High energy particles
• Are attracted to (+)ve protons in the nucleus
– keeps them close together
• Constant energy of motion prevents them
from collapsing into nucleus
• Exact path of travel cannot be known
• An electron’s energy confines it to an energy
level within the electron cloud
• Electrons with higher energy occupy energy
levels farther from the nucleus
Orbitals
• Energy levels contain orbitals which can only
hold a certain number of electrons.
Energy
Level
1
# of orbitals
1
Maximum #
of electrons
2
2
4
8
3
9
18
Expanding the Bohr Model
Example: A carbon atom
We know:
From periodic table
• atomic number of carbon equals six;
• therefore the number of electrons equals six
Why?
From previous chart
• first energy level holds two electrons
maximum
• second energy level holds eight electrons
maximum
Expanding the Bohr Model
Putting it all together:
Two of carbon’s electrons will
be found in the first energy
level of the electron cloud.
The remaining four electrons
will be found in the second
energy level of the
electron cloud.
The second energy level of a
carbon atom is not full. It
can still accommodate four
more electrons.
= neutron
= proton
= electron
Homework:
Bohr-ing Practice
Using the worksheet provided as a
guide, draw Bohr models for the listed
atoms. Complete the summary tables
for each atom after you have drawn
them.
HOMEWORK!!
Obj. 2
Glossary – Part 1
matter – anything that occupies space and has
mass
mass – quantity of matter an object has
element – a substance that cannot be broken
down chemically into simpler substances
atom – simplest particle of an element that
retains all of the properties of that element
compound – a substance containing atoms of
two or more elements that are chemically
combined in fixed proportions
trace element – an element that makes up less
than 0.01% of your body mass
Glossary – Part 2
organic compound – a compound that contains
the element carbon
orbitals – a three-dimensional region around a
nucleus that indicates a probably location of
an electron
isotopes – atoms of the same element that have
a different number of neutrons
chemical bonds – attractive forces that hold
atoms together
Works Cited
Campbell, Neil A., Brad Williamson, and Robin J. Heyden.
Biology: Exploring Life. Upper Saddle River, NJ: Pearson
Education, 2004.
Emsley, John. The Elements. 3rd. Oxford: Clarendon Press, 1998.
Postlethwait, John H., and Janet L. Hopson. Modern Biology. Austin,
TX: Holt, Rinehart and Winston, 2006.
"Radiation Therapy Career Overview." May School of Health
Sciences. 2003. Mayo Foundation for Medical Education and
Research. 28 Sep 2008 <www.mayo.edu/mshs/rtcareer.html>.