Unit 2:Unit 2: All Biology is All Biology is ChemistryChemistryLesson 2:Lesson 2: The The Chemistry of LifeChemistry of Life

DrillDrill30 September 200830 September 2008

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.

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ObjectivesObjectives

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 Atom –The Simplest of ParticlesThe 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.”

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The Structure of an AtomThe 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 ModelThe Bohr ModelBelow is a Bohr Model of a helium (He) atom.

n +n+

NucleNucleusus 2 protons2 neutronsneutrons

Electron Electron cloudcloudConsists of orbitals where high-energy electrons orbit the nucleus

Subatomic ParticlesSubatomic 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

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Electrons Negatively (-) charged particles Mass is negligible (1/1840 amu) Remain in constant motion in orbitals

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Another Look at the Periodic Another Look at the Periodic TableTable

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Atomic Number

Atomically Speaking…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…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 = proton

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Isotopes: Isotopes: Not All Atoms are Created EqualNot 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

= neutron = proton

Click here to Click here to compare these compare these

two atoms.two atoms. These two atoms are 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.

These two atoms are 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.

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Isotope:

from the from the Greek Greek isosisos, , meaning meaning “equal” “equal” and and topostopos, , meaning meaning “place”“place”

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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 ElectronsA 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

OrbitalsOrbitals

• Energy levels contain orbitals which can only hold a certain number of electrons.

Energy Energy LevelLevel

# of # of orbitalsorbitals

Maximum Maximum # of # of

electronselectrons

11 11 22

22 44 88

33 99 1818

Expanding the Bohr ModelExpanding the Bohr Model

Example: A carbon atomWe 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

= neutron = proton = electron

Expanding the Bohr ModelExpanding 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.

Homework: Homework: Bohr-ing PracticeBohr-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!!

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Glossary – Part 1Glossary – Part 1

matter – anything that occupies space and has mass

mass – quantity of matter an object haselement – 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 2Glossary – 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 CitedWorks 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/rt-career.html>.