Chemistry

Chemistry

The universe is a vast soup of interacting particles and energy. The ways in which those interactions take place, as well as the structure and composition of matter, is the main focus of the field of chemistry. Our chemistry learning modules introduce you to the world of chemistry, exploring current research and scientific findings on concepts like the structure and function of atoms, forms of energy and its transfer, chemical bonding and reactions, and more.

misconception:

The gas state of a substance weighs less than the liquid or solid state.


Tracking the development of our understanding of the atomic structure of matter, this module begins with the contributions of ancient Greeks, who proposed that matter is made up of small particles. The module then describes how Lavoisier's Law of Conservation of Mass and Proust's Law of Definite Proportions contributed to Dalton's modern atomic theory.

Modern atomic theory has evolved dramatically from the 19th century view of the atom as a small, solid sphere resembling a billiard ball. This module explores that story: from the discovery of electrons and protons in the late 19th century to the planetary model of the atom in the early 20th century. The module explains the function of subatomic particles as well as their relative size and weight. The concepts of atomic number and atomic mass are introduced.

The 20th century brought a major shift in our understanding of the atom, from the planetary model that Ernest Rutherford proposed to Niels Bohr’s application of quantum theory and waves to the behavior of electrons. With a focus on Bohr’s work, the developments explored in this module were based on the advancements of many scientists over time and laid the groundwork for future scientists to build upon further. The module also describes James Chadwick’s discovery of the neutron. Among other topics are anions, cations, and isotopes.

  • Drawing on experimental and theoretical evidence, Niels Bohr changed the paradigm of modern atomic theory from one that was based on physical particles and classical physics, to one based in quantum principles.
  • Under Bohr’s model of the atom, electrons cannot rotate freely around the atom, but are bound to certain atomic orbitals that both constrain and define an atoms electronic behavior.
  • Atoms can gain or lose electrons to become electrically charged ions.
  • James Chadwick completed the early picture of the atom with his discovery of the neutron, a neutral, nuclear particle that affects an atom’s mass and the different physical properties of atomic isotopes.

The modern periodic table is based on Dmitri Mendeleev’s 1896 observations that chemical elements can be grouped according to chemical properties they exhibit. This module explains the arrangement of elements in the period table. It defines periods and groups and describes how various electron configurations affect the properties of the atom.

This lesson is an introduction to the history and use of the scientific concept of the mole.

The process of diffusion is critical to life, as it is necessary when our lungs exchange gas during breathing and when our cells take in nutrients. This module explains diffusion and describes factors that influence the process. The module looks at historical developments in our understanding of diffusion, from observations of “dancing” particles in the first century BCE to the discovery of Brownian motion to more recent experiments. Topics include concentration gradients, the diffusion coefficient, and advection.

  • Diffusion is the process by which molecules move through a substance, seemingly down a concentration gradient, because of the random molecular motion and collision between particles.
  • Many factors influence the rate at which diffusion takes place, including the medium through with a substance is diffusing, the size of molecules diffusing, the temperature of the materials, and the distance molecules travel between collisions.
  • The diffusion coefficient, or diffusivity, provides a relative measure at specific conditions of the speed at which two substances will diffuse into one another.

Solids are formed when the forces holding atoms or molecules together are stronger than the energy moving them apart. This module shows how the structure and composition of various solids determine their properties, including conductivity, solubility, density, and melting point. The module distinguishes the two main categories of solids: crystalline and amorphous. It then describes the four types of crystalline solids: molecular, network, ionic, and metallic. A look at different solids makes clear how atomic and molecular structure drives function.

  • A solid is a collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and size.
  • There are two main categories of solids: crystalline and amorphous. Crystalline solids are well ordered at the atomic level, and amorphous solids are disordered.
  • There are four different types of crystalline solids: molecular solids, network solids, ionic solids, and metallic solids. A solid's atomic-level structure and composition determine many of its macroscopic properties, including, for example, electrical and heat conductivity, density, and solubility.

There are many states of matter beyond solids, liquids, and gases, including plasmas, condensates, superfluids, supersolids, and strange matter. This module introduces Kinetic Molecular Theory, which explains how the energy of atoms and molecules results in different states of matter. The module also explains the process of phase transitions in matter.

This module provides an introduction to the chemical properties of water. The dipole across the molecule, hydrogen bonding, surface tension,and solvation are all introduced.

Chemical bonding between atoms results in compounds that can be very different from the parent atoms. This module, the second in a series on chemical reactions, describes how atoms gain, lose, or share electrons to form ionic or covalent bonds. The module lists features of ionic and covalent compounds. Lewis dot structures and dipoles are introduced.

When scientists want to describe a chemical reaction in writing, they use precise chemical equations. This module, the third in a series on chemical reactions, explains chemical equations in a step-by-step process. The module shows how chemical equations are balanced in the context of the chemical changes that take place during a reaction. The Law of Conservation of Matter is introduced.

Since acids and bases were first labeled and described in the 17th century, their definition has been refined over the centuries to reflect an increased understanding of their chemical properties. This module introduces the fundamentals of acid/base chemistry, including neutralization reactions. The relationship between hydrogen ion concentration [H+] and pH is shown alongside everyday examples of acids and bases.

Exploring the how and why of chemical reactions, this module describes properties of the inert – or "noble" – gases. It also explains how different elements achieve a stable configuration by bonding to fill their valence shells with electrons, resulting in a chemical compound. The difference between exothermic and endothermic reactions is discussed.

Beginning with the work of Marie Curie and others, this module traces the development of nuclear chemistry. It describes different types of radiation: alpha, beta, and gamma. The module then applies the principle of half-life to radioactive decay and explains the difference between nuclear fission and nuclear fusion.

The chemical basis of all living organisms is linked to the way that carbon bonds with other atoms. This introduction to organic chemistry explains the many ways that carbon and hydrogen form bonds. Basic hydrocarbon nomenclature is described, including alkanes, alkenes, alkynes, and isomers. Functional groups of atoms within organic molecules are discussed.

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