Biology 107Biology 107

Chemical Context of LifeChemical Context of Life

August 30, 2002August 30, 2002

Chemical Context of LifeChemical Context of LifeStudent Objectives:Student Objectives: As a result of this lecture and the assigned reading, As a result of this lecture and the assigned reading,

you should understand the following:you should understand the following:

1.1. The six (6) major elements in living systems are: The six (6) major elements in living systems are: carbon, hydrogen, nitrogen, carbon, hydrogen, nitrogen, oxygen, phosphorus, oxygen, phosphorus, and and sulfur (CHNOPS)sulfur (CHNOPS)..

2.2. The number of protons in a nucleus determines the The number of protons in a nucleus determines the atomic numberatomic number, and it is , and it is different for each element. The total number of protons and neutrons is the different for each element. The total number of protons and neutrons is the atomic mass numberatomic mass number..

3.3. It is mainly the electrons and the different energy levels of electrons in It is mainly the electrons and the different energy levels of electrons in electron shellselectron shells that determine how an atom behaves when it encounters other that determine how an atom behaves when it encounters other atoms. atoms. The number of electrons in the outermost shell determine the chemical The number of electrons in the outermost shell determine the chemical properties of an atomproperties of an atom..

Chemical Context of LifeChemical Context of Life

4.4. When electrons move from higher electron shells to lower shells When electrons move from higher electron shells to lower shells they give off energy. Conversely, energy must be supplied to move they give off energy. Conversely, energy must be supplied to move electrons from lower to higher shells (e.g., photosynthesis, where electrons from lower to higher shells (e.g., photosynthesis, where light energy raises electrons to higher shells).light energy raises electrons to higher shells).

5.5. Atoms with filled outer shells tend to be relatively inactive (inert), Atoms with filled outer shells tend to be relatively inactive (inert), while atoms whose outer shell is not full tend to interact with other while atoms whose outer shell is not full tend to interact with other atoms by participating in chemical reactions that result in the filling atoms by participating in chemical reactions that result in the filling or emptying of a shell. Atoms may share or transfer electrons of the or emptying of a shell. Atoms may share or transfer electrons of the outer shell. These interactions typically result in atoms staying close outer shell. These interactions typically result in atoms staying close together, held together by attractions called chemical bonds. together, held together by attractions called chemical bonds.

6.6. Chemical bonds may be ionic or covalent (polar or non-polar).Chemical bonds may be ionic or covalent (polar or non-polar).

7.7. Atoms and molecules may also interact through intermolecular Atoms and molecules may also interact through intermolecular forces that are not chemical bonds (e.g., hydrogen bonds). forces that are not chemical bonds (e.g., hydrogen bonds).

The number of electrons in the outermost shell determine The number of electrons in the outermost shell determine the chemical properties of an atomthe chemical properties of an atom

The number of electrons in the outermost shell The number of electrons in the outermost shell determine the chemical properties of an atomdetermine the chemical properties of an atom

When electrons move from higher electron shells When electrons move from higher electron shells to lower shells they give off energyto lower shells they give off energy

When electrons move from higher electron When electrons move from higher electron shells to lower shells they give off energyshells to lower shells they give off energy

Atoms participate in chemical reactions by sharing Atoms participate in chemical reactions by sharing or transferring electrons of the outer shell to result or transferring electrons of the outer shell to result

in the filling or emptying of a shellin the filling or emptying of a shell

Atoms participate in chemical reactions by sharing Atoms participate in chemical reactions by sharing or transferring electrons of the outer shell to result or transferring electrons of the outer shell to result

in the filling or emptying of a shellin the filling or emptying of a shell

Ionic chemical bonds result from the transfer of Ionic chemical bonds result from the transfer of electrons - Videoelectrons - Video

Covalent chemical bonds result from the Covalent chemical bonds result from the sharing of electronssharing of electrons

Covalent chemical bonds result from the Covalent chemical bonds result from the sharing of electronssharing of electrons

Covalent chemical bonds result from the Covalent chemical bonds result from the sharing of electrons - Videosharing of electrons - Video

Covalent chemical bonds which share Covalent chemical bonds which share electrons equally are electrons equally are non-polarnon-polar

Covalent chemical bonds which share Covalent chemical bonds which share electrons unequally are electrons unequally are polarpolar

Covalent bonding - Video