Chapter-2-The Chemical Contex of Life

Chapter-2
The Chemistry of Life

 

Chemistry-the study of the physical and chemical properties of matter.

Matter-anything that has weight(mass), occupies space and has permanence.

Matter exists as____, ____ and ____?

Matter can change from one form to another.

 

Centigrade and Fahrenheit

F to C F-32 x 5/9

Example: Convert 212oF to C.

212-32 x 5/9 = 180 x 5/9 = 100

C to F. C x 9/5 + 32

Example: Convert 100oC to F

100 x 9/5+32 = 180 + 32 = 212

 

Solids , Liquids and Gases

Solid- definite shape and definite volume

Liquid- definite volume, no definite shape.

Gas- no definite volume, no definite shape.

 

Regardless of which state matter exists it always has the same chemical composition.

Example- Water. Ice, liquid, steam (gas) = H2O

The states in which matter exists depends upon the speed of the molecules, which is determined by heat.

 

 

Composition of Matter:
Elements,Compounds,Mixtures

Element- a substance that cannot be broken down chemically into 2 or more different kinds of atoms

Atom- the smallest particle of an element that displays the properties of that element.

Molecule- a chemical union of 2 or more atoms which may be the same or different.

 

Compound- a substance formed by the chemical union of 2 or more different elements. Hydrogen + oxygen = H2O

This always results in a definite ratio of each element in the compound.

 

Mixture- combinations of different elements or compounds in no particular proportion and usually with no chemical union. Usually they can easily be separated apart.

Water + Sand

Salt + Water

Sand + Iron filings

 

Organic and Inorganic

Organic- an organic compound is one that contains the element_______?

Inorganic- a compound that does not contain_________?

 

Subatomic particles

All atoms are composed of 3 basic particles

These subatomic particles are ___,___,___

 

Atomic number and Atomic Weight

Atomic Number- the atomic number of an element tells us: (1) How many protons an element has and (2) How many electrons it has.

Atomic weight or mass - tells us the combined number of protons and neutrons an element has.

 

Atomic mass or weight minus the Atomic number = the number of neutrons.

Example: Sodium has an atomic number of 11 and an atomic weight of 23. Therefore sodium has 23-11= 12 neutrons

 

Isotopes

Isotope- a different form of the same element. The difference is in the number of neutrons.

Example- there are 3 different forms of the element Carbon. Their atomic numbers are the same but their atomic weights are different.

Carbon 12, Carbon 13 and Carbon 14.

Some Isotopes are Radioactive

A radioactive isotope is one that emits radioactive particles or rays

Alpha particle- 2 protons + 2 neutrons

Beta particle- an electron

Gamma rays and X -Rays.

All of these particles or rays can damage living material.

 

Isotopes are Useful

Dating of fossils

Tracers

Medical treatments

Nuclear power

 

Radioactive Isotopes are Used to Date Fossils and Rocks

Each radioactive isotope decays at a certain rate into another element.

The time it takes for ½ of a radioactive element to decay into another element is called its half-life.

Example K40 1.25 billion years Ar40

 

Why is the atomic weight number of an element unequal?

The atomic weight you see on your charts is an average weight of all the isotopes of that element. The average weight is based on the proportion of each isotope in an element

Example: If I have a sample of carbon it is actually composed of three isotopes of carbon (C12, C13 and C14) with a certain % of each isotope in the sample.

 

Electron Shells

Electrons orbit the nucleus of an atom in electron shells. There are 7 electron shells.

Each shell can hold a certain number of electrons.

Lets look at the first 4 shells

 

Electron Shells

We will look now at the first 4 electron shells.

 

Valence and Valence Electrons

Valence electrons-the number of electrons in the outer shell of an atom

Valence- the number of electrons required to complete an atom’s outer shell

The bonding of atoms is dependent on the number of electrons in the outer shell

 

Types of Chemical Bonds

Covalent bond- a type of bond in which electrons are shared between atoms so that their outer shells are complete.

In general outer shells are complete when they have either 2 or 8 electrons in these shells.(even if it can hold more than 8)

 

 

 

Covalent Bonds are of Two Types

1.Electrons shared equally (nonpolar)

Examples: Hydrogen gas H2

Fluorine gas F2

2.Electrons not shared equally (polar)

Example: Water H2O

 

 

Ionic Bonding

Ionic bond- when electrons are transferred from one element to another. This results in charged atoms (ions) which can be either positive (+) or negative (-)

Example: Table salt NaCl

Cation- a positive ion

Anion- a negative ion

 

Hydrogen Bonds

Hydrogen bond- formed when the slightly positive hydrogen atom in one molecule is attracted to the slightly negative atom in another molecule.

This bond is between separate molecules not within molecules

Example: The attraction between 2 separate water molecules. H2O````H2O

 

Van der Waals Interactions

These are weak bonds formed by localized charge fluctuations between close atoms or molecules.

Even a nonpolar molecule will at any particular moment have charged areas due to the constant motion of electrons.

 

Chemical Equations

Represent chemical reactions between elements

H2 + O2 >>>>> H2O

Since matter can be neither created or destroyed during a chemical reaction we must balance the equation

2H2 + O2 >>>>> 2H2O

 

A molecules biological function is related to its shape

A molecule has a characteristic size and shape. The precise shape of a molecule is very important to its function in the living cell