Atoms, molecules, and chemical bonds form the foundation of life's chemistry. They're the building blocks that make up everything from water to DNA. Understanding these basics is crucial for grasping how our bodies work at the molecular level.
Chemical bonds hold atoms together, creating the molecules essential for life. Ionic, covalent, and hydrogen bonds each play unique roles in biological processes, from maintaining cell structure to enabling DNA replication and protein function.
Atomic Structure and Components
Subatomic Particles
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Atoms are the smallest unit of matter that retain the properties of an element
Composed of subatomic particles called protons, neutrons, and electrons
Protons are positively charged particles located in the nucleus at the center of an atom
The number of protons in an atom determines the element's atomic number and identity
Neutrons are electrically neutral particles also located in the nucleus
Contribute to the mass of the atom but do not affect the element's identity
Electrons are negatively charged particles that orbit the nucleus in shells or orbitals
The arrangement of electrons in these orbitals determines an atom's chemical properties and bonding behavior
Isotopes
Atoms of an element have the same number of protons but can vary in their number of neutrons
Results in different isotopes of the same element
Isotopes have different atomic masses but maintain the same chemical properties (carbon-12, carbon-13, carbon-14)
Chemical Bonds and Properties
Types of Chemical Bonds
Chemical bonds are the attractive forces that hold atoms together to form molecules or compounds
The three main types of chemical bonds are ionic, covalent, and metallic bonds
Ionic bonds form when electrons are completely transferred from one atom to another
Results in positively and negatively charged ions that attract each other (sodium chloride, NaCl)
Covalent bonds form when atoms share electrons to achieve a stable electronic configuration
Can be single, double, or triple depending on the number of electron pairs shared (water, H2O; carbon dioxide, CO2)
Metallic bonds occur in metals where valence electrons are delocalized and shared among many atoms
Creates a "sea of electrons" that gives metals their characteristic properties (copper, Cu; aluminum, Al)
Bond Properties
Ionic compounds have high melting points, are brittle as solids, and conduct electricity when dissolved in water
Covalent compounds have lower melting points, are often gases or liquids at room temperature, and do not conduct electricity
Metals have high electrical and thermal conductivity, malleability, and ductility due to their bonding arrangement
Ionic vs Covalent vs Hydrogen Bonds
Ionic and Covalent Bonds
Ionic bonds involve the complete transfer of electrons from one atom to another
Typically occur between a metal and a nonmetal (potassium iodide, KI)
Covalent bonds involve the sharing of electrons between atoms to achieve a stable electronic configuration
Can be polar or nonpolar, depending on the electronegativity difference between the bonded atoms
Nonpolar covalent bonds occur when electrons are shared equally between atoms with similar electronegativities (hydrogen gas, H2; chlorine gas, Cl2)
Polar covalent bonds occur when electrons are shared unequally due to differences in electronegativity (water, H2O; hydrogen chloride, HCl)
Hydrogen Bonds
Hydrogen bonds are a special type of intermolecular force
Occurs between a hydrogen atom bonded to a highly electronegative atom (such as N, O, or F) and another electronegative atom nearby
Weaker than ionic or covalent bonds but play a crucial role in the properties of water and the structure of biological molecules (DNA, proteins)
Chemical Bonds in Biological Molecules
Covalent Bonds in Organic Compounds
Chemical bonds are essential for the formation and function of biological molecules (carbohydrates, lipids, proteins, nucleic acids)
Covalent bonds, particularly carbon-carbon and carbon-hydrogen bonds, form the backbone of most biological molecules
The ability of carbon to form stable single, double, and triple bonds allows for the diversity of organic compounds found in living organisms
Hydrogen Bonds in Biological Structures
Hydrogen bonds play a crucial role in the structure and function of many biological molecules
In water, hydrogen bonds between molecules give rise to properties such as cohesion, adhesion, and high specific heat capacity, which are essential for life
In DNA, hydrogen bonds between complementary base pairs (A-T and G-C) stabilize the double helix structure and enable the storage and replication of genetic information
In proteins, hydrogen bonds between amino acids contribute to the formation of secondary structures (alpha helices, beta sheets), which ultimately determine the protein's three-dimensional shape and function
Ionic Bonds in Cellular Functions
Ionic bonds, while less common in biological molecules, are important for maintaining proper cell function
Electrolytes like sodium (Na+), potassium (K+), and chloride (Cl-) ions are involved in nerve impulse transmission, muscle contraction, and maintaining osmotic balance