Basic Chemistry

Published on 01/06/2015 by admin

Filed under Pulmolory and Respiratory

Last modified 01/06/2015

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 3131 times

Basic Chemistry

Atomic Structure

Atom: The smallest subdivision of a substance that still maintains the properties of that substance, frequently referred to as the building blocks of the universe. An atom is composed of the following (Figure 1-1):

Element: General term applied to each of the 109 specifically named different types of atoms.

Isotope: Atom of a substance with the same number of protons but with a varying number of neutrons. All elements have at least two isotopes. The following are the three primary isotopes of oxygen:

0-16,8 neutrons(99.76% of all oxygen)

0-17,9 neutrons(0.04% of all oxygen)

0-18,10 neutrons(0.20% of all oxygen)

Atomic weight: Average weight of an atom of a particular substance based on its comparison with the atomic weight of the carbon 12 isotope. The atomic weight is approximately equal to the sum of the number of protons and neutrons in the nucleus of an atom but is not a whole number because of the presence of isotopes (Table 1-1).

TABLE 1-1

Symbol, Atomic Number, Atomic Weight, and Valence of the 26 Elements Commonly Found in the Human Body and Other Elements Commonly Seen in Medicine

Element Symbol Atomic No. Atomic Weight Valence
Elements Commonly Seen in the Body
Aluminum Al 13 26.98 +3
Boron B 5 10.83 +3
Calcium Ca 20 40.08 +2
Carbon C 6 12.0 + or − 4
Chlorine Cl 17 35.5 − 1
Chromium Cr 24 51.99 − 1 or − 2
Cobalt Co 27 58.93 +2
Copper Cu 29 63.55 + 1 or +2
Fluorine F 9 18.99 − 1
Hydrogen H 1 1.00 +1
Iodine I 53 126.9 − 1
Iron Fe 26 55.84 + 1 or +2
Magnesium Mg 12 24.31 +2
Manganese Mn 25 54.94 − 2 or − 3
Molybdenum Mo 42 95.94 − 1 or − 2
Nitrogen N 7 14.01 − 3
Oxygen O 8 15.99 − 2
Phosphorus P 15 30.97 − 3
Potassium K 19 39.09 +1
Selenium Se 34 78.96 − 2
Silicone Si 14 28.09 + or − 4
Sodium Na 11 22.98 +1
Sulfur S 16 32.06 − 2
Tin Sn 50 118.7 + or − 4
Vanadium V 23 50.94 − 2 or − 3
Zinc Zn 40 91.22 + 1 or +2
Other Elements Commonly Seen in Medicine
Barium Ba 56 137.34 +2
Gallium Ga 31 69.72 +3
Helium He 2 4.00 + or − 2
Lead Pb 82 207.19 + 1 or +2
Lithium Li 3 6.94 +1
Mercury Hg 80 200.59 + 1 or +2

image

Gram atomic weight: Mass in grams of an element equal to its atomic weight (see Table 1-1).

Atomic number: Equal to the number of protons in the nucleus of an atom (see Table 1-1).

Ion: Charged species of a particular atom; occurs as a result of the loss or gain of electrons from an atom.

II Molecular Structure

Molecule: Particle that results from the chemical combination of two or more atoms normally having a neutral charge but may be positively or negatively charged.

Compound: Molecule formed from two or more elements.

Free radical: A charged compound, reacting as any other ion reacts.

Molecular formula: Chemical expression indicating the types and number of atoms in a molecule. The particle that is positively charged is usually listed first.

    Examples:

    NaCl = 1 sodium atom and 1 chloride atom contained in the molecule.

    H2SO4 = 2 hydrogen atoms, 1 sulfur atom, and 4 oxygen atoms contained in the molecule.

Molecular weight (MW): Sum total of all individual atomic weights of atoms that make up a molecule.

    Example (H2SO4):

Atom No. of Atoms   Atomic Weight Total Contributing Weight
H 2 × 1 2
S 1 × 32 32
O 4 × 16 64
        MW 98

image

    Example (CO2):

Atom No. of Atoms   Atomic Weight Total Contributing Weight
C 1 × 12 12
O 2 × 16 32
        MW 44

image

Gram molecular weight (GMW): Mass in grams of a molecule equal to its MW.

One mole of a substance is equal to one GMW of the substance.

III Valence

Valence: Number given to an atom that indicates its tendency to gain or lose electrons in a chemical reaction.

    Examples (see Table 1-1):

    

Na+1 (sodium): Valence of +1 indicates that in a chemical reaction it will react by losing one electrons.
Ca+2 (calcium): Valence of +2 indicates that in a chemical reaction it will react by losing two electrons.
F−1 (fluorine): Valence of − 1 indicates that in a chemical reaction it will react by gaining one electron.

Generally, valences of elements allow predictions of their chemical reactivity with each other.

Inert gases (noble gases) have an electron distribution that has full outer orbitals. These elements (e.g., helium, neon, argon, krypton, and xenon) do not react with other elements under normal atmospheric conditions.

IV Types of Chemical Compounds

Ionic compound: A compound formed by atoms in the compound transferring electrons, one atom gaining and the other losing electrons. Ionic compounds form ions when dissolved in solution.

    Examples:

NaCl: Na+1 has a valence of +1, and Cl−1 has a valence of − 1. The Na+1 atom has lost an electron, and the Cl− 1 atom has gained an electron during the formation of NaCl.
CaF2: Ca+2 has a valence of +2, and each F−1 atom has a valence of − 1. The Ca+2 atom has lost two electrons, and each F− 1 atom has gained one electron during the formation of CaF2.

    

Covalent compound: A compound formed by the sharing of electrons between the various atoms in the compound. In solution the molecule does not disassociate into its component parts.

O−2 + O−2 → O2

N−3 + N−3 → N2

Cl−1 + Cl−1 → Cl2

Hydrogen bonding (polar covalent compound): An intermediate compound between a pure covalent compound and an ionic compound characterized by an incomplete (partial) sharing of electrons. In solution the molecule only partially disassociates into its component parts.

    Examples:

H+1 + OH−1 → H2O

H2O + CO2 → H2CO3

Types of Chemical Reactions

VI Volume Percent and Gram Percent

VII Chemical Solutions

Solution: Homogeneous mixture of two substances.

Solute: Substance dissolved in a solution.

Solvent: Substance that is the dissolving agent.

Effects of a solute on the physical characteristics of water:

As the temperature of the solvent increases, the volume of solute that can be dissolved in the solvent also increases.

Dilute solution: A solution with a small amount of solute dissolved in each unit of solvent at a particular temperature.

Saturated solution: A solution with the maximum amount of solute dissolved in each unit of solvent at a particular temperature. In a saturated solution a precipitate is seen at the bottom of the solution.

Supersaturated solution: A solution with a greater amount of solute than the solvent would normally hold, dissolved at a particular temperature. However, any physical disturbance of this solution causes the excess solute to precipitate.

Precipitate: A crystallized solid formed at the bottom of a saturated solution.

VIII Solution Concentrations

Ratio solution: Solution concentration represented as a ratio (1:100) between solute and solvent in number of grams to number of milliliters.

    Examples:

    2:500 means 2 g to 500 ml: 2 indicates the number of grams of solute, and 500 indicates the number of milliliters of solvent.

    1:1000 means 1 g to 1000 ml: 1 indicates the number of grams of solute, and 1000 indicates the number of milliliters of solvent.

    Problems:

Percent weight/volume (w/v): Solution concentration in which the actual percentage indicates the number of grams of solute per 100 ml of solution.

    Example:

    1% w/v solution means 1 g of solute is contained in 100 ml of solution.

    Problems:

True percent solution: Solution concentration in which solute and solvent are expressed in either weight (% w/w) or volume (%v/v). The solute is expressed as a true percentage of the solution.

    Examples:

    10% w/w solution, where the total solution volume is 100 g, there is 10 g of solute and 90 g of solvent.

    3% v/v solution, where the total solution volume is 500 ml, there is 15 ml of solute and 485 ml of solvent.

    Problems: