Matter, Atoms, and Elements

Matter, Atoms, and Elements

• Matter occupies space, possesses mass, and exists as a solid, liquid, gas, or plasma.
• An element cannot be broken down into other substances via chemical means; 25 of the 118 elements are essential for human life.
• An atom is matter's smallest unit with elemental properties, composed of protons, neutrons, and electrons.
• Protons have a positive charge and reside in the nucleus, determining the atomic number.
• Neutrons have a neutral charge and reside in the nucleus, contributing to the atom's mass number.
• Electrons have a negative charge, orbit the nucleus in electron shells, and participate in chemical bonding.
• Atomic number signifies the number of protons in an atom's nucleus, defining the element's place on the periodic table.
• Mass number is the total count of protons and neutrons in an atom's nucleus, measured in atomic mass units (amu).
• Isotopes are variations of an element with the same proton number but differing neutron numbers, leading to different mass numbers; some are radioactive, like Carbon-14.
• Electron shells represent energy levels around the nucleus where electrons are situated, filling from the lowest energy level outward, with the outermost shell being the valence shell.
• Valence electrons are in an atom's outermost shell.
• Valence electrons dictate reactivity, influencing interactions with other atoms to achieve a full valence shell (octet rule).

Chemical Bonds

• A chemical bond is an attractive force joining atoms, forming as atoms interact to gain a stable electron configuration, usually a full valence shell.
• Ionic bonds arise from electron transfer between atoms, creating ions.
• Cations are positively charged ions formed by losing electrons.
• Anions are negatively charged ions formed by gaining electrons.
• NaCl (sodium chloride) is an example where Na loses an electron to become Na+, and Cl gains one to become Cl-, attracting each other to form the bond.
• Covalent bonds are formed by sharing electrons between atoms.
• Nonpolar covalent bonds involve equal electron sharing between atoms with similar electronegativity, such as O2 (oxygen gas).
• Polar covalent bonds involve unequal electron sharing between atoms with differing electronegativity, exemplified by H2O (water), producing partial charges (δ+ and δ-).
• Electronegativity describes an atom's attraction for electrons in a covalent bond; higher electronegativity indicates a stronger pull on shared electrons.
• A hydrogen bond is a weak bond between a slightly positive hydrogen atom and a slightly negative atom, like oxygen or nitrogen, crucial for water’s properties and biological molecule structure.

Water Properties

• Water's characteristics stem from polar covalent bonds and hydrogen bonding.
• High specific heat means resistance to temperature changes.
• High heat of vaporization means requiring substantial energy for liquid to gas transition (evaporative cooling).
• Cohesion refers to water molecules sticking together due to hydrogen bonds.
• Adhesion refers to water molecules sticking to other polar substances.
• Surface tension is the force causing a liquid's surface to contract.
• Water is an excellent solvent capable of dissolving many polar and ionic substances.
• Ice is less dense than liquid water.
• A solution is a homogeneous mixture.
• A solvent dissolves the solute.
• A solute is dissolved in the solvent.
• An aqueous solution uses water as the solvent.

Acids, Bases, and pH

• An acid donates hydrogen ions (H+), increasing the H+ concentration in a solution.
• A base accepts hydrogen ions (H+) or donates hydroxide ions (OH-), decreasing the H+ concentration in a solution.
• The pH scale measures acidity/basicity from 0 to 14.
• A pH of 0-7 is acidic with higher H+ concentration.
• A pH of 7 is neutral.
• A pH of 7-14 is basic with higher OH- concentration.
• Each pH unit signifies a tenfold change in H+ concentration.
• A buffer resists pH changes by accepting or donating H+ ions, which maintains stable pH in biological systems.

Macromolecules

• Macromolecules are large polymers containing smaller monomer subunits.
• Carbohydrates consist of monosaccharides (simple sugars) and serve in energy storage and structural support.
• Lipids consist of fatty acids and glycerol, providing energy storage, insulation, and form cell membranes.
• Proteins consist of amino acids and have roles as enzymes, perform structural work, transport substances, and signaling.
• Nucleic acids consist of nucleotides and store/transmit genetic information (DNA and RNA).
• Dehydration reactions link monomers, removing water molecules to form polymers.
• Hydrolysis breaks polymers by adding water molecules, which decomposes polymers into monomers.

Nucleic Acids and Proteins

• DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) carry genetic information.
• Nucleic acids consist of nucleotides.
• Sugars are deoxyribose (DNA) or ribose (RNA).
• Components include a phosphate group, and nitrogenous base: adenine (A), guanine (G), cytosine (C), thymine (T) in DNA; uracil (U) replaces thymine in RNA.
• DNA is usually double-stranded, and RNA is typically single-stranded.
• Proteins are amino acid polymers.
• Proteins have multiple functions: enzymes, structural support, transport, signaling, etc..
• Amino acids contain an amino group (-NH2), a carboxyl group (-COOH), and an R group(side chain).
• Properties of amino acids are determined by the R group, which varies among the 20 different amino acids.
• Proteins exhibit four structure levels: primary (amino acid sequence), secondary (alpha-helices and beta-sheets), tertiary (3D folding), and quaternary (multiple polypeptide chains).

Life's Characteristics and Organization

• Order refers to highly organized structures.
• Growth and development refer to increases in size and complexity.
• Energy processing refers to how living things obtain and utilize energy.
• Evolutionary adaptation describes changes over time responding to the environment.
• Reproduction is the ability to produce offspring.
• Regulation maintains internal stability (homeostasis).
• Response to stimuli is the ability to react to environmental changes.
• A cell is the basic unit of life and all living things are composed of cells.
• Prokaryotic cells (bacteria and archaea) lack a nucleus.
• Eukaryotic cells (plants, animals, fungi, protists) have a nucleus and other membrane-bound organelles.
• Life’s organization unfolds as atoms → molecules → organelles → cells → tissues → organs → organ systems → organisms → populations → communities → ecosystems → biosphere.
• Emergent properties manifest at each hierarchical level.

The Scientific Method

• The scientific method systematically explores the natural world.
• Observation is the first step.
• A question is formed based on observations.
• A hypothesis (testable explanation) is proposed.
• A prediction is made based on the hypothesis.
• An experiment is conducted, manipulating one variable in a controlled setting.
• Data Analysis is performed.
• A conclusion is drawn to support or refute the hypothesis.
• Communication of results.
• A hypothesis is a testable explanation that can be supported or refuted, but never definitively proven.
• A theory is a well-supported explanation backed by extensive evidence, offering a broad understanding of nature.