Elements Of Life

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Animals > Organ Systems > Organs > Tissues > c Cells

Water and Carbon
Dr. Corl
BIOL 105
August 23, 2013

The Elements of Life

Most important: Hydrogen, Carbon, Nitrogen and

• Four types of atoms comprise 96% of the matter in living organisms:
– Hydrogen, _______, ________, and _______.

Valence Electrons

1) valence 2) filled 3)bonding
An atom is happiest when it's valence shell is full

• Atoms often have unpaired electrons in their _________
(outermost) shells.
• Atoms are most stable when their valence shells are _____.
• Atoms can interact with each other in ways that help fill their valence shells, resulting in chemical ________.



Types of Chemical Bonds

1) Nonpolar 2) Polar 3) Ionic

1.) Covalent bond: Results when two atoms share their valence electrons in order to fill their valence shells.
- ________ covalent bond:
Electrons are evenly shared
- ________ covalent bond:
Electrons are asymmetrically shared
2.) _______ bond: Results when one atom completely transfers electrons to another atom.

Covalent Chemical Bonds

• Covalent bonds result from electron ______.

Polar vs. Nonpolar Covalent Bonds

Electrons are being shared.

1) sharing

Atoms of different elements sharing electrons with each each other may lead to one element holding shared shared electrons more strongly.
1) Oxygen 2) tightly
O > N > C > H (electronegativity)
Water is a polar molecule: regions of partial pos

• ______ has a high electronegativity and holds shared electrons more ______ than hydrogen.

and neg charge.



Ionic Bonds

Ionic bonds can occur between negatively and positively charged ions (cations and anions)
1) electrons 2) Ions 3) opposite

• Results from a complete transfer of _______ from one atom to another.
• _____ formed in this manner have _________ charges and are attracted to one another.

Single, Double, and Triple
Covalent Bonds

Single: participants share 1 pair of electrons
Double: sharing 2 pairs of electrons

• Atoms with more than one ______ valence electron can form _______ covalent bonds.

Representation of Molecules

Chemical formulas tell you how many of each element make up a molecule.
Structural formulas show you how they are arranged. 3


Water: H2O

Water is the most abundant molecule within the living cell. 1) cells 2) solvent

• Living ____ are over 75% water (by volume).
• Our bodies are ~70% water (by mass).
• Water is a great ________ - an agent for getting substances into solution.

Water is a Polar Molecule

Hydrogen bond
1)oxygen 2) hydrogen
Each water molecule can form up to 4 hydrogen bo bonds. These bonds help water molecules to stick

• ______ bond:

to one another.

– A weak bond that forms between an atom with a partial positive charge and an atom with a partial negative charge.
– e.g. A hydrogen bond can form between the partial negatively charged _______ of one water molecule and the partial positively charged ________ of a second water molecule.

Water as a Solvent

1) Polar 2) Hydrophilic

• _____molecules and ions are _______:
They dissolve readily in water



Water as a Solvent

1) Nonpolar 2) hydrophobic
Lipids are dominated by a relatively nonpolar stucture structure. They do not dissolve in water.

• _______molecules are __________:
They do not dissolve readily in water

Special Properties of Water

1) LESS 2) open

• Solid water (ice) is _____ dense than liquid water, allowing ice to float atop liquid water.
– Water molecules in ice, making the maximum number of hydrogen bonds with neighboring water molecules, are locked together in a relatively _____ crystal lattice.

Water is Cohesive and Adhesive
• ________: Clinging together of like molecules: – Water molecules cohere together via hydrogen bonding.