Bio Chap 2
Chemical Context of Life: A Summary
The sources describe the chemical context of life, examining how the structure of atoms and their bonding behavior impact the formation and function of molecules, driving the chemical reactions essential for life.
Matter and Its Building Blocks
Matter is defined as anything that takes up space and has mass.
Matter comprises elements, which cannot be broken down into simpler substances by chemical reactions.
Elements combine in fixed ratios to form compounds, which possess properties distinct from their constituent elements.
For instance, table salt (NaCl) is a compound with different properties than the elements sodium (a metal) and chlorine (a poisonous gas).
Atomic Structure: Subatomic Particles and Isotopes
Atoms are the smallest unit of matter that retains the properties of an element.
Atoms consist of three subatomic particles: protons, neutrons, and electrons.
Protons carry a positive (+) charge, while electrons carry a negative (-) charge.
Neutrons have no charge.
The number of protons in an atom's nucleus defines its atomic number.
The mass number is the sum of protons and neutrons in the nucleus.
The atomic mass represents the weighted average mass of the naturally occurring isotopes of an element.
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.
While isotopes have the same chemical properties due to their identical electron arrangements, they differ in mass.
Many isotopes are radioactive, meaning they spontaneously decay, emitting particles and energy.
Radioactive isotopes have various applications, including as diagnostic tools in medicine (radioactive tracers) and for dating fossils and rocks (radiometric dating).
Chemical Bonds: The Foundation of Molecular Structure
Chemical bonds result from the interactions between atoms seeking to complete their valence shells.
The most important types of chemical bonds are covalent bonds and ionic bonds.
Covalent bonds form when two atoms share one or more pairs of valence electrons.
The electronegativity of an atom determines its ability to attract electrons in a covalent bond.
Non-polar covalent bonds occur when electrons are shared equally between atoms with similar electronegativities, as in H2 and O2.
Polar covalent bonds form when atoms with differing electronegativities share electrons unequally, resulting in partial charges (δ+ and δ-) within the molecule, such as in H2O.
Ionic bonds result from the transfer of an electron from one atom to another, creating ions with opposite charges that attract each other.
The atom that loses an electron becomes a cation (positively charged), while the atom that gains an electron becomes an anion (negatively charged).
Ionic compounds, or salts, are formed by the attraction between cations and anions, arranging themselves in a three-dimensional lattice.
Weak Chemical Interactions
Weak chemical interactions, including hydrogen bonds and van der Waals interactions, are vital in biological systems, influencing the three-dimensional shapes and interactions of molecules.
Hydrogen bonds occur when a hydrogen atom covalently linked to a highly electronegative atom (like oxygen or nitrogen) is attracted to another electronegative atom nearby.
Van der Waals interactions arise from temporary fluctuations in electron distribution within molecules, creating fleeting regions of positive and negative charge that allow atoms and molecules to stick together.
Molecular Shape and Function
The spatial arrangement of atoms within a molecule, determined by the positions of the atoms' orbitals, plays a critical role in molecular function.
Molecular shape influences how biological molecules recognize and interact with one another.
For instance, morphine's ability to bind to endorphin receptors in the brain highlights how molecular shape influences biological activity.
The concept of molecular mimicry exemplifies this phenomenon, where molecules with similar shapes can bind to the same receptors and elicit comparable effects.
Chemical Reactions: Rearranging Matter
Chemical reactions involve the making and breaking of chemical bonds, leading to changes in the composition of matter.
In chemical equations, reactants are the starting materials, and products are the substances formed.
Photosynthesis is a crucial biological example, showcasing how chemical reactions rearrange atoms to create new molecules.
During photosynthesis, plants utilize sunlight to convert carbon dioxide and water into glucose and oxygen.
Chemical reactions are fundamentally reversible and strive for chemical equilibrium, a state where the forward and reverse reactions occur at the same rate, leading to stable concentrations of reactants and products.
This summary covers all the chapter objectives listed in and.