Life’s Chemical BasisChapter 2

Elements• Fundamental forms of

matter

• Can’t be broken apart by normal means

• 92 occur naturally on Earth

Most Common Elements in Human Body (98%)

Oxygen

Hydrogen

Carbon

Nitrogen

Calcium

What Are Atoms?• Smallest particles that retain

properties of an element

• Made up of subatomic particles:

– Protons (+) located in the nucleus

– Neutrons (no charge) located in the nucleus

– Electrons (-) located in space around the nucleus

Atomic Number(whole # on the periodic table)

• = the # of protons• All atoms of a specific element have

the same atomic #• Atomic # of hydrogen = 1• Atomic # of carbon = 6• Atomic # of helium = 2• If you change the # of protons, you

change the atom into a different element

Atomic Mass (decimal # on the periodic table)

Number of protons

+Number of neutrons

So why is it a decimal number? You’ll soon

find out….

What is the role of neutrons?

• Since protons have a + charge, they repel each other

• Neutrons are neutral and help to stabilize the nucleus – think police

The Organization of the Periodic Table: Based on ELECTRONS!

Why Electrons Matter

• Atoms acquire, share, and donate electrons

• Whether an atom will interact with other atoms depends on how many electrons it has

Electrons

• Carry a negative charge• Also repel one another • Attracted to protons in the

nucleus• Move in volumes of space

that surround the nucleus

Shell Model• The shell model of electron orbitals

diagrams electron vacancies, filled from inside out

• Each shell represents an energy level:– 1st shell: (2 electrons)– 2nd shell: (8 electrons)– 3rd shell: (8 electrons)

• Atoms with vacancies in their outer shell tend to give up, acquire, or share electrons

CALCIUM20p+ , 20e-

Electron Vacancies

• Unfilled levels make atoms more likely to react with other atoms

• Hydrogen, carbon, and nitrogen are examples of elements with vacancies in their outer levels

CARBON6p+ , 6e-

NITROGEN7p+ , 7e-

HYDROGEN1p+ , 1e-

Ion Formation• Atoms that lose electron(s),

become positively charged ions (cations)

• Atoms that gain electron(s), become negatively charged ions (anions)

• Electronegativity:– A measure of an atom’s

ability to pull electrons from another atom

- -

proton

neutron

electron

He

Atomic Structure: Helium

- --- -

-

-

N

Atomic Structure: Nitrogen

HYDROGEN

electron

proton

neutron

Atomic Structure of Hydrogen

Isotopes: What are They?• Atoms of an element with the SAME # of

protons, but a DIFFERENT # of neutrons

• The atomic mass # on the periodic table is an avg. mass of all the different isotopes possible for the element

• How do you figure out the number of neutrons in an atom? Atomic mass – atomic number = #

neutrons

“Carbon 12” has 6 protons, 6 neutrons

“Carbon 14” has 6 protons, 8 neutrons

Special Isotopes: Radioactive Isotopes

• Have an unstable nucleus

that emits energy or some

of the subatomic particles

(protons or neutrons)• Some are used in research

and medical applications (pacemakers, radiation therapy, MRI)

Radioactive Isotopes Can be Used as Tracers

• A tracer is a substance with a radioactive isotope attached to it

• Emissions from the tracer can be detected with special devices

• Following the movement of tracers is useful in many areas of biology and medicine

Next Lecture…

Chemical Bonds!

Lab 3: Making Conversions Between Various Lab 3: Making Conversions Between Various Measuring SystemsMeasuring Systems

• Purpose of this lab:

To become familiar with several systems of measurement and make conversions from one unit to another as well as learn to read syringes and graduated cylinders