Topic 2

 

Basic Chemical Concepts

A. Matter

Matter . Any substance which has mass and occupies space. All physical objects are composed of matter in the form of atoms, which are composed of protons, neutrons, and electrons. It is the material of which the universe is composed and exists in three forms: solids, liquids, gases.

B. Components of Matter

1. Element - A substance which cannot be decomposed by ordinary chemical means. There are 118 elements now known that singly or in combination constitute all matter and are described in the periodic table. Ex. N, P, K, Au, Ag, H, O

 

For any element:

Number of Protons = Atomic Number

Number of Electrons = Number of Protons = Atomic Number

Number of Neutrons = Mass Number - Atomic Number

 

2. Atom - Smallest particle of an element that maintains its chemical identity.3. A compound is a complex substance that can be decomposed by chemical methods into simpler substances.

4. Molecule - A chemical combination of two or more atoms which form a specific chemical substance. To break up the molecule into its constituent atoms is to change its character.

 

Carbon dioxide molecule CO2

An atomic diagram of carbon dioxide, or CO2, showing its protons, neutrons and electrons including the carbon and oxygen atoms stock photography

Water molecule H2O

 

An atomic diagram of water, or H20, showing its protons, neutrons and electrons including the hydrogen and oxygen atoms Stock Photo - 5785443

C. Atomic weight`

The relative weight of one atom of an element compared with the weight of one atom of carbon (12) or one atom of oxygen (16).

O =16, H =1, N = 14, Au = 197

Also the sum of protons and neutrons in the nucleus

 

D. Molecular weight

The sum of the atomic weights of all the atoms of any one molecule

H2O 1+1+16 = 18

KCl 39+35 = 74

E. Equivalent weight

The atomic weight of an element divided by the valence it assumes in a chemical compound.

Atomic weight divided by the valence= equivalent weight

equivalent weight of K = 39/1 = 39, Ca = 40/2 =20

F. Ions

An ion is an atom or group of atoms that have a net electric charge

Na loses an electron Na+

Cl gains an electron Cl-

 

a. Cation - A positively charged atom or group of atoms

NH4+ , K+, Al+++, Ca++

 

b. Anion - A negatively charged atom or group of atoms

NO3-, H2PO4- , HPO4=, Cl-, SO4=

Ions with the same charge repel while opposite charges attract.

Ca++ repels H+

Ca++ attracts SO=4

Soil Colloids - (clay and organic matter) are negatively charged; therefore they attract cations.

H+

Mg++ Ca++

Al++ K+

Anions such as NO- 3, SO=4, and Cl- move freely in the soil. they are not retained by soil colloids.

Phosphate is a special case anion. It does not move freely in the soil because it forms insoluble compounds with iron and aluminum in acid soils and calcium in high pH soils.

C HOPKiNS CaFe Managed By Mine CuZins, Mo and Claude
C H O P K N S CaFe Mg B Mn CuZn Mo Cl

 

 

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