The Nature of Molecules and the Properties of Water

Elements
Chemical Bonds
Atoms
Atoms, Atomic Structure, Elements, Chemical Bonds, Molecules, Water, Acids and Bases
Acidic
Water
pH Scale
Neutral
Alkaline
Acids & Bases
JCU

Know what electrons, protons, and neutrons are.
How the number of valence electrons of an atom relates to its chemical properties.
The principal chemical elements of living things.
Distinguish covalent bonds, hydrogen bonds, and ionic bonds.
How hydrogen bonds between adjacent water molecules govern many of the properties of water.
Why all of the above are important to living systems, including humans!

Matter: Any substance in the universe that has mass and occupies space.
- Everything around you is made of matter.
- Matter can have different phases: Solid, Liquid, or Gas.
Atom: Fundamental unit of matter, composed of protons, neutrons, and electrons.
- Size: Atoms are tiny, approximately 0.1 nm in diameter.
- Atoms differ because objects can be made up of different kinds of atoms.

Atoms consist of three sub-atomic particles:
- Protons: Positively charged particles located in the nucleus.
- Neutrons: Neutral particles also located in the nucleus.
- Electrons: Negatively charged particles that orbit the nucleus in areas called orbitals or valence shells.
- The positive charge of the protons keeps electrons from flying out of orbit.

Analogy: If an atom was the size of an apple, the apple would be as large as the Earth.

An Element: Any substance that cannot be broken down into simpler substances by ordinary chemical means.
- Examples: Gold (Au) derived from Latin "aurum".
The Periodic Table includes all known elements, each having a unique chemical symbol and atomic number.

Living organisms primarily consist of four major elements making up 96.3% of their mass:
- Oxygen (O): 65%
- Carbon (C): 18.5%
- Hydrogen (H): 9.5%
- Nitrogen (N): 3.2%
Additional macro-nutrients: Phosphorus (P), Calcium (Ca), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg).
Trace elements are also important: Iron (Fe), Zinc (Zn), etc., which are required in very small amounts but play vital roles in biological processes.

Isotopes: Atoms of a single element with different numbers of neutrons.
- Radioactive Isotopes: Unstable, emitting radiation during decay, useful in medical applications (e.g., imaging).
- Half-life: Time required for half of the radioactive atoms in a sample to decay.

Molecules: Groups of atoms held together in a stable association.
- Compounds: Molecules containing more than one type of element (e.g., H₂O, CO₂).
- Properties of compounds differ from the elements that compose them.

Ionic Bonds:
- Ions form from the loss or gain of electrons.
- Sodium (Na) loses an electron to form Na⁺, while Chloride (Cl) gains an electron to form Cl⁻, with an electrostatic attraction between oppositely charged ions forming an ionic bond (e.g., NaCl).
Covalent Bonds:
- Formed when two elements with similar electronegativity share electrons to complete their valence shells.
- Types of covalent bonds:
  - Single Bond: H–H (Hydrogen gas)
  - Double Bond: O=O (Oxygen gas)
  - Triple Bond: N≡N (Nitrogen gas)
Polar Covalent Bonds:
- Occurs when one atom has higher electronegativity than another, resulting in unequal sharing of electrons.
- Example: Water (H₂O) has polar covalent bonds due to oxygen’s higher electronegativity.

Water is essential for life and is characterized by hydrogen bonding between molecules.
- Polarity: Water molecules exhibit polar properties due to the high electronegativity of oxygen.
- Cohesion: Water molecules attract each other, leading to high surface tension.
- Adhesion: Water can stick to other polar molecules, which is evident in the meniscus of water.

High Specific Heat: Requires significant energy input to change its temperature.
High Heat of Vaporization: Evaporation of water causes cooling.
Less Dense as a Solid: Ice floats on liquid water, as solid water (ice) is less dense than its liquid form.
Good Solvent: Water dissolves polar molecules and ions.
Hydrophobic & Hydrophilic Interactions: Water organizes nonpolar molecules.

The pH scale measures hydrogen ion concentration in solutions:
- Pure water has a [H⁺] of 10^(-7) (neutral pH = 7).
- Acid: Any substance that increases [H⁺] in solution and decreases pH.
- Base: Any substance that lowers [H⁺] by binding with hydrogen ions, increasing pH.

Buffers: Resist changes in pH by absorbing excess H⁺ or releasing H⁺ when base is added.
- Composed of a weak acid and its corresponding base (e.g., Carbonic acid (H₂CO₃) and Bicarbonate ion (HCO₃⁻)).

Knowledge of elements, atoms, and their properties is crucial in fields like chemistry, biology, environmental science, and medicine.
Understanding the molecular makeup and interactions of substances leads to advances in various real-world applications, from pharmaceuticals to environmental conservation.