Chapter 2

The Chemistry of Life

Section 2.1: The Nature of Matter

• We are all walking, talking chemistry experiments!!– We are made from chemical compounds– We use chemical reactions to keep us alive

• Since chemistry is so critical to life, we need to start here with the “behind-the-scenes” stuff to understand the “chemistry” of life.

Matter• Matter – the building blocks or the “stuff”

that everything is made of (yes, even non-living things too!)

• About 2500 years ago, a Greek philosopher named Democritus made some observations with chalk– He wondered, if you keep breaking a piece of chalk, is it still

considered chalk?

– He believed that eventually you would get to the point where you could not break the chalk anymore

– He called this smallest piece an atom which means unable to be cut

Atoms• An atom is the basic unit of matter• Atoms are very smallsmall

100 million atoms would fit across the width of your pinky finger!!100 million atoms would fit across the width of your pinky finger!!

• Even though atoms are very small, they contain Even though atoms are very small, they contain particles within them called particles within them called subatomic particlessubatomic particles that are even smaller!that are even smaller!

• The The subatomic particles subatomic particles that make up atoms are:that make up atoms are:1) 1) protonsprotons2) 2) neutronsneutrons3) 3) electronselectrons

Nucleus

• Protons are positively (+) charged particles• Neutrons are particles with no charge• Protons and neutrons have about the same

mass

• Together, these subatomic particles make up the nucleus of an atom– The nucleus is the center of the atom

Electrons• Electrons are negatively (-) charged particles

• Electrons have 1/1840 the mass of a proton

• Electrons can be found in a “cloud” around the nucleus and they are in constant motion– They are attracted to the positively charged nucleus

(opposites attract!!), but they stay outside of the nucleus because of all of the energy of their motion

Charge of an Atom

• Atoms have an equal number of protons and electrons so the positive and negative charges balance out

– This means that atoms are electrically neutral

http://www.youtube.com/watch?v=lP57gEWcisY&feature=related

The Atom’s Family

• http://www.youtube.com/watch?v=sshZjxmzJVI&feature=related

The Atoms Family

1st Verse:

They’re tiny and they’re teeny,

Much smaller than a beany,

They never can be seeny,

The Atoms Family

Chorus:

They are so small (snap, snap)

They’re round like a ball (snap, snap)

They make up the air.

They’re everywhere.

Can’t see them at all (snap, snap)

2nd Verse:Together they make gases,And liquids like molasses,And all the solid masses,The Atoms Family

Chorus

3rd Verse:

Neutrons can be found,

Where protons hang around;

Electrons they surround

The Atoms Family

Chorus

The Atom’s FamilyEXTRA CREDIT OPPORTUNITY

• Either by yourself, with a partner, or a small group, perform the Atom’s Family song and video tape it! You can then save the video clip on a flash drive, CD, or your school account. The video needs to be school appropriate and the more creative, the more extra credit points! You can earn up to 10 extra credit points.

Elements

• An element is a pure substance that is made completely of only one type of atom

• There are more than 100 known elements but only about 24 are found in living things

Elements

• Atomic symbol- the symbols used to represent an element (one or two letters)

i.e. Carbon’s atomic symbol is: C

• Atomic number- the number of protons in the nucleus of an element

• i.e. Carbon’s atomic number is : 6

Isotopes• Isotopes are atoms of the same element that

have a different number of neutronsi.e. Carbon atoms (which always have 6 protons) can have

six, seven, and even eight neutrons!

http://www.google.com/imgres?q=isotopes+of+carbon&hl=en&sa=X&tbm=isch&prmd=ivns&tbnid=o38ZsHvYHwHfFM:&imgrefurl=http://misterhaggins.edu.glogster.com/isotopes/&docid=Ynw5N7PABznusM&w=556&h=328&ei=AcJsTuGhG4ODtger-9XrBQ&zoom=1&biw=1366&bih=566&iact=rc&dur=195&page=1&tbnh=94&tbnw=159&start=0&ndsp=22&ved=1t:429,r:0,s:0&tx=88&ty=58

Isotopes cont…• Mass Number- the total number of protons

and neutrons in the nucleus of an atom– We identify the isotopes according to their

mass number (Figure 2-3, p. 35)

i.e. carbon-12, carbon-13, carbon 14

• Atomic Mass- the weighted average of the masses of an element’s isotopes (the abundance of each isotope in nature is considered when this average is calculated)

http://www.gwadi.org/tools/tracers/carbon

Radioactive Isotopes• Some isotopes have unstable nuclei that break

down at a constant rate over time

• This radiation can be dangerous, but can also be important!

• Can determine the age of rocks based on the isotopes found in them

• Radiation can be used to detect and treat cancer• Can kill bacteria that cause food to spoil• Can be used as “tracers” within living things to “trace” the

movements of substances within them

Chemical Compounds• A compound is a substance that is formed by

the chemical combination of 2 or more elements in definite proportions

• A compound can be represented by a chemical formula

i.e. the chemical formula for water is H2O

Water has 2 hydrogen atoms for every 1 oxygen atom so these

atoms combine in a 2:1 ratio

Properties of Compounds• The physical and chemical properties of a

compound are very different from the properties of the elements that make it

• i.e. hydrogen and oxygen are both gases at room temperature by themselves, but when they are together, they form liquid water

http://www.brooklyn.cuny.edu/bc/ahp/SDgraphics/PSgraphics/SD.PS.LG.Water.html

Chemical Bonds• The atoms within a compound are held

together by chemical bonds

• These bonds are the result of interactions between the electrons that surround each atom

• Valence electrons- the electrons that are in the outer electron shell of an atom that can form bonds with other atoms

• There are 2 main types of chemical bonds:1) Ionic Bonds

2) Covalent Bonds

Ionic Bonds• An ionic bond is formed when one or more

electrons are transferred from one atom to another

• If an atom loses electrons, it becomes positively charged (there are more protons than electrons)

• If an atom gains electrons, it becomes negatively charged (there are more electrons than protons)

• Ions – Atoms that are positively or negatively charged

• See p. 37, Figure 2-4 A

Covalent Bonds• A covalent bond is formed when electrons

are shared between atoms• The electrons can move around the nuclei of both

atoms

• When only one electron is shared, it is a single covalent bond. When four are shared, it’s a double bond and when six are shared it’s a triple bond.

• As a result of sharing electrons, the atoms are joined together and a molecule is formed

• See p. 37, Figure 2-4 B

Molecules

• Molecules are the smallest unit of most compounds

• They are formed when two or more atoms are bonded together

Van der Waals Forces

• Some atoms have the ability to attract electrons

• Some have a stronger ability than others

• When atoms share electrons in a covalent bond, the sharing is not always equal

• This means that a molecule may have regions that are slightly positive and slightly negative

• This can play a role in the properties of a molecule (i.e. water molecule)

Van der Waals Forces

• When molecules are close together, a slight attraction can develop between these regions that are oppositely charged

• These intermolecular (between molecules) forces are called Van der Waals forces

• These forces are not as strong as ionic or covalent bonds, but they can still hold molecules together

• See p.39