Subatomic Particles of the Atom

Protons, Neutrons, and Electrons

Atoms are compofsed of three main subatomic particles: protons, neutrons, and electrons. Understanding their properties is essential for grasping atomic structure and chemical behavior in biological systems.

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

• Neutrons: Neutral particles also found in the nucleus. They contribute to the atomic mass but do not affect charge.

• 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

Definition and Biological Use

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses. Some isotopes are stable, while others are radioactive and decay over time.

• Radioisotope: An isotope that emits radiation as it decays. Used in biological research for tracing molecules and imaging.

• Example: Carbon-14 is used in radiolabeling to track metabolic pathways.

Valence Electrons and Chemical Bonding

Role in Reactivity and Periodic Table Trends

Valence electrons are the electrons in the outermost shell of an atom. They determine how atoms interact and bond with each other.

• Elements in the same group of the periodic table have the same number of valence electrons, leading to similar chemical properties.

• Chemical reactivity is influenced by the tendency to gain, lose, or share valence electrons.

• Example: Group 1 elements (e.g., sodium, potassium) have one valence electron and are highly reactive.

Molecules vs. Compounds

Definitions and Examples

A molecule is two or more atoms bonded together. A compound is a molecule that contains atoms of different elements.

• Molecule: O2 (oxygen gas) consists of two oxygen atoms.

• Compound: H2O (water) consists of hydrogen and oxygen atoms.

Ionic vs. Covalent Bonds

Comparison and Biological Impact

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). Important for forming salts and maintaining cellular ion gradients.

• Covalent bonds: Occur between nonmetals (e.g., H2O, CH4). Essential for stable biological molecules like proteins and DNA.

• Effect on structure/function: Covalent bonds provide stability; ionic bonds can dissociate in water, affecting molecule function.

Unique Properties of Water

Cohesion, High Heat Capacity, Solvent Abilities

Water exhibits several unique properties that are vital for life:

• Cohesion: Water molecules stick together due to hydrogen bonding, enabling surface tension.

• High heat capacity: Water absorbs and retains heat, helping organisms maintain temperature.

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

• Support for life: These properties enable nutrient transport, temperature regulation, and cellular processes.

Hydrogen Bonding and Water's Polarity

Origin and Biological Importance

Hydrogen bonds arise from water's polarity, where the oxygen atom is slightly negative and hydrogen is slightly positive.

• Polarity: Unequal sharing of electrons creates partial charges.

• Biological importance: Hydrogen bonds stabilize DNA, proteins, and enable water's unique properties.

Polar Molecules and Solubility

Influence of Molecular Polarity

Polar molecules dissolve well in water due to interactions between partial charges and water's polarity.

• Hydrophilic substances: Polar molecules (e.g., sugars, salts) are soluble in water.

• Hydrophobic substances: Nonpolar molecules (e.g., oils) do not dissolve in water.

pH and Biological Buffers

Definition, Importance, and Buffer Systems

pH measures the concentration of hydrogen ions () in a solution. Biological systems use buffers to maintain stable pH and homeostasis.

• Acids: Substances that donate ions.

• Bases: Substances that accept ions.

• Buffer: A solution that resists changes in pH by neutralizing added acids or bases.

• Bicarbonate buffer system: Maintains blood pH in humans.

Equation:

Capillary Action

Mechanism and Examples

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

• Why it happens: Water molecules adhere to surfaces and cohere to each other, pulling the liquid upward.

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