Atoms

Definition and Structure of Atoms

Atoms are the basic units of matter and the defining structure of elements. They consist of subatomic particles that determine the properties and behavior of each element.

• Atom: The smallest unit of matter that retains the properties of an element.

• Subatomic particles: Include protons, neutrons, and electrons.

  • Proton: Positive charge, mass of 1.

  • Neutron: No charge, mass of 1.

  • Electron: Negative charge, negligible mass (not included in atomic mass calculations).

Matter

Elements and Atomic Composition

Matter is composed of elements, which are made up of atoms. Elements are organized in the periodic table and have unique properties.

• There are 92 elements that occur naturally.

• Atoms of different elements have different numbers of protons.

• Atoms can gain or lose electrons from the valence shell, affecting their chemical behavior.

• Six elements (C, H, O, N, P, S) are fundamental molecular components of all organisms.

• Atomic Mass: Number of protons + number of neutrons.

Neutrons, Isotopes, & Electrons

Isotopes and Electron Behavior

Isotopes and electrons play crucial roles in the chemical properties and stability of atoms.

• Neutrons: Number determined by isotopes.

  • Atomic mass number: Number of protons + number of neutrons.

  • Isotopes: Atoms of the same element with different numbers of neutrons. Some isotopes are stable, others are radioactive (unstable).

• Electrons: Determine how atoms interact (bonding ability).

Atomic Structure

Electron Shells and Orbitals

Electrons are located in orbitals arranged in shells around the nucleus. The arrangement affects chemical reactivity.

• Orbitals are filled in a specific sequence.

• The outermost shell (valence shell) determines how atoms bond.

• If the valence shell is full, the atom is stable; if not, it will react with other atoms.

• Reactive atoms have unpaired electrons in their outermost shell.

• The energy level of each shell increases with distance from the nucleus.

Molecules

Formation and Properties of Molecules

Molecules are pure substances containing only one kind of atom or combinations of atoms bonded together.

• Molecule: Made up of a neutral group of two or more atoms held together by chemical bonds.

• Compound: Molecule made of two or more elements bonded together in a fixed ratio.

Chemical Bonds

Types and Properties of Chemical Bonds

Chemical bonds are attractive forces that link atoms together, forming molecules. They determine the structure and function of molecules.

• Shared electrons: Covalent bonds.

• Polar covalent bonds: Atoms share electron pairs unequally. Occurs when two atoms are different; the more electronegative atom pulls the shared electrons closer to itself (e.g., H2O structure).

• Nonpolar covalent bonds: Atoms share electron pairs equally. Occurs when two atoms are identical (except for C-H bonds).

Ions and Ionic Bonds

Formation and Properties of Ions

Ions are electrically charged particles formed when atoms lose or gain electrons. Ionic bonds are attractions between oppositely charged ions.

• Cations: Positive charge.

• Anions: Negative charge.

• Ionic bond: Attraction between a positive ion and a negative ion (e.g., Na+ and Cl- in NaCl).

• Ionic bonds are weak in water and dissolve easily.

Hydrogen Bonds

Properties and Biological Importance

Hydrogen bonds are weak attractions that occur between polar molecules, especially involving hydrogen and electronegative atoms like oxygen or nitrogen.

• Bond with O and N.

• Contribute to surface tension, cohesion, and specific heat.

Chemical Reactions

Reactants, Products, and Conservation of Matter

Chemical reactions involve the making and breaking of chemical bonds, transforming reactants into products.

• Reactants: Starting materials in a chemical reaction.

• Products: Final molecules produced by the reaction.

• Law of Conservation of Matter: A chemical reaction cannot create or destroy matter.

Example equation:

Water: Properties and Importance

Water as a Polar Molecule

Water is a polar molecule and an excellent solvent, making it essential for biochemical reactions.

• Polarity: Water molecules have a positive and negative end.

• Solvent: Dissolves many substances, important for life.

Hydrogen Bonding in Water

Hydrogen bonds form between water molecules, giving water unique properties.

• Hydrogen bonds are strong enough to hold water molecules together but weak enough to break and reform easily.

Specific Heat of Water

Water has a high specific heat, meaning it can absorb or release large amounts of heat with little temperature change.

• 1 gram of water requires 1 calorie to raise its temperature by 1 degree Celsius.

• Helps regulate temperature in organisms and environments.

High Heat of Vaporization

Water requires a large amount of energy to change from liquid to gas, which helps moderate climate and organism temperature.

• Heat of vaporization: Energy required to convert water from liquid to gas.

• Evaporation removes heat from surfaces, resulting in cooling.

Ice Floats

Ice is less dense than liquid water, allowing it to float and insulate aquatic environments.

• Density = Mass / Volume.

• Ice acts as an insulator and moderates temperature flux.

Cohesion and Surface Tension

Water molecules stick together (cohesion) and create surface tension due to hydrogen bonding.

• Cohesion: Water molecules resist separation.

• Surface tension: Water molecules at the surface are hydrogen-bonded to other water molecules below.

Water as Acid and Base

Water can act as both an acid and a base due to the reactive nature of hydrogen ions.

• Hydrogen ions can modify pH levels.

Acids and Bases

Definitions and Properties

Acids release hydrogen ions in solution, while bases accept hydrogen ions.

• Strong acids: Ionize fully (e.g., HCl).

• Weak bases: Do not ionize fully.

Acidity and Alkalinity

pH Scale and Biological Relevance

The pH scale measures the concentration of hydrogen ions in a solution, affecting biological processes.

• Water is neutral (pH 7).

• Acidic solutions: pH < 7 (e.g., beer, tomato juice, battery acid).

• Basic solutions: pH > 7 (e.g., bleach).

• Most biological fluids have pH levels between 6 and 8.

Impacts on Biological Systems

pH and Biological Reactions

pH influences the rates of biological reactions and can change the structure of biological molecules.

• Enzyme activity and molecular stability are affected by pH.

Homeostasis: Maintaining pH

Buffer Systems and pH Regulation

Living organisms use buffer systems to maintain constant internal conditions (homeostasis), especially pH.

• Buffers consist of a weak acid and its corresponding base.

• Buffers help maintain a constant pH by neutralizing excess acids or bases.

*Additional info: Some explanations and examples have been expanded for clarity and completeness.*