Atomic Chemistry

The Basic building blocks of life

  • Importance of understanding the basic components of life and compounds.

    • What are we made of?

    • Building blocks of every living organism.

    • Basic composition of a compound and its properties.

Basic Composition of Life

  • Matter: Anything that occupies space and has mass.

  • Element: Cannot be broken down by ordinary chemical means.

    • 92 elements recognized in nature.

    • Approximately 25 elements are essential for life, along with trace elements.

Chemical Composition of the Human Body (Table 2.1)

Element

Symbol

Percentage of Human Body Weight

Oxygen

O

65.0%

Carbon

C

18.5%

Hydrogen

H

9.5%

Nitrogen

N

3.3%

Calcium

Ca

1.5%

Phosphorus

P

1.0%

Potassium

K

0.4%

Sulfur

S

0.3%

Sodium

Na

0.2%

Chlorine

Cl

0.2%

Magnesium

Mg

0.1%

Trace Elements (less than 0.01%): boron, chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, selenium, silicon, tin, vanadium, zinc.

Most Common Elements in Living Matter

  • Electrons determine atom behavior.

    • Electrons in different shells have varying energies (2 in the 1st shell, 8 in the 2nd, and 16 in the 3rd shell).

  • Key elements: Hydrogen (H), Carbon (C), Nitrogen (N), Oxygen (O).

    • All have unshared pairs of electrons, increasing their reactivity.

Trace Elements

  • Essential for life in small quantities (e.g., iodine for thyroid hormone production).

    • Iodine deficiency can cause goiter; hence iodine is added to table salt.

Compounds

  • A compound consists of two or more elements in fixed proportions (e.g., H2O, NaCl, CO2, NH3).

  • Rare to find pure elements in nature.

Structure of Atoms

  • Atoms: smallest unit of matter retaining properties of an element.

  • Made of subatomic particles:

    • Protons: Positive charge.

    • Neutrons: No charge.

    • Electrons: Negative charge, found in the electron cloud around the nucleus.

Identifying Atoms

  • Atomic Number: Number of protons.

  • Atomic Mass: Sum of protons and neutrons.

Isotopes

  • Isotopes have the same number of protons but different numbers of neutrons.

    • Example: 32P is a radioactive isotope.

  • Uses of radioactive isotopes:

    • Medical tracers for diagnosis.

    • Potential harm from uncontrolled exposure.

Chemical Bonds

  1. Ionic Bonds

    • Formed when oppositely charged ions attract.

    • Example: Sodium (Na) gives up an electron to Chlorine (Cl) to form NaCl.

  2. Covalent Bonds

    • Atoms share electrons to fill outer shells.

    • Can be:

      • Nonpolar: Equal sharing (e.g., H2, O2).

      • Polar: Unequal sharing (e.g., H2O).

Electron Arrangement and Bonding

  • Outermost shell holds 8 electrons for stability.

  • Electronegativity: An atom’s attraction for electrons.

Properties of Water

  • Hydrogen bonds lead to unique properties:

    1. Cohesion: Strength of water molecules attracting each other.

    2. Surface Tension: Ability to hold drops on surfaces.

    3. Solvent Properties: Water as a biological solvent.

    4. Moderation of Temperature: Water's high heat of vaporization.

    5. Density: Ice is less dense than liquid water, allowing it to float.

Chemical Bonding

  • Atoms bond to achieve stability and fill their outer electron shells to lower energy states.