Atomic Structure and Subatomic Particles

Subatomic Particles: Protons, Neutrons, and Electrons

Atoms are composed of three main subatomic particles: protons, neutrons, and electrons. Each particle has distinct properties and plays a specific role in atomic structure.

• Protons: Positively charged particles located in the nucleus. They determine the atomic number and identity of an element.

• Neutrons: Neutral particles also found in the nucleus. They contribute to the atomic mass and can vary in number, resulting in isotopes.

• Electrons: Negatively charged particles that orbit the nucleus in electron shells. They are involved in chemical bonding and reactions.

• Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Isotopes and Their Biological Applications

Definition and Use of Radioisotopes

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses. Radioisotopes are unstable isotopes that emit radiation as they decay.

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

• Biological Use: Radioisotopes such as Carbon-14 are used in radiometric dating and as tracers in biological research to track molecular processes.

• Example: Phosphorus-32 is used to label DNA in molecular biology experiments.

Valence Electrons and Chemical Bonding

Role of Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. They determine an atom's chemical reactivity and bonding characteristics.

• Influence on Reactivity: Atoms with similar numbers of valence electrons (same group in the periodic table) have similar chemical properties.

• Example: All Group 1 elements (alkali metals) have one valence electron and react similarly.

Molecules and Compounds

Definitions and Examples

Molecules are two or more atoms bonded together. Compounds are molecules composed of different elements.

• Molecule Example: O2 (oxygen gas)

• Compound Example: H2O (water)

• Difference: All compounds are molecules, but not all molecules are compounds.

Ionic and Covalent Bonds

Comparison and Biological Significance

Ionic bonds form when electrons are transferred from one atom to another, creating charged ions. Covalent bonds form when atoms share electrons.

• Ionic Bonds: Occur between metals and nonmetals; e.g., NaCl (table salt).

• Covalent Bonds: Occur between nonmetals; e.g., H2O (water).

• Effect on Biological Molecules: Covalent bonds provide stability to organic molecules; ionic bonds are important in physiological processes.

Properties of Water

Unique Properties and Biological Importance

Water exhibits several unique properties due to its molecular structure and hydrogen bonding.

• Cohesion: Water molecules stick to each other, aiding in transport in plants.

• High Heat Capacity: Water absorbs and retains heat, stabilizing temperatures in organisms and environments.

• Solvent Abilities: Water dissolves many substances, facilitating biochemical reactions.

• Example: Water supports life by enabling nutrient transport and temperature regulation.

Hydrogen Bonding and Water's Polarity

Formation and Biological Importance

Hydrogen bonds arise from the polarity of water molecules, where the oxygen atom is slightly negative and the hydrogen atoms are slightly positive.

• Formation: The positive region of one water molecule is attracted to the negative region of another.

• Biological Importance: Hydrogen bonds stabilize DNA structure, proteins, and contribute to water's unique properties.

Molecular Polarity and Solubility

Influence on Solubility

Polarity refers to the distribution of electrical charge over a molecule. Polar molecules dissolve well in water, a polar solvent.

• Effect: Polar substances (e.g., sugars, salts) are soluble in water; nonpolar substances (e.g., oils) are not.

pH, Acids, Bases, and Buffers in Biological Systems

Definitions and Importance

pH measures the concentration of hydrogen ions in a solution. Acids release H+ ions; bases accept H+ ions. Buffers stabilize pH by neutralizing excess acids or bases.

• Importance: Maintaining pH is crucial for enzyme function and metabolic processes.

• Buffer Example: The bicarbonate buffer system in blood helps maintain homeostasis.

Capillary Action

Explanation and Examples

Capillary action is the movement of liquid through narrow spaces due to cohesion and adhesion.

• Why It Happens: Water molecules adhere to surfaces and cohere to each other, allowing upward movement against gravity.

• Examples from Nature: Water transport in plant xylem; movement of water in soil.