Radiometric Dating Tulane University


The committee developed four core ideas in the physical sciences three of which parallel those identified in previous documents, including the National Science Education Standards and Benchmarks for Science Literacy [, ]. The three core ideas are PS6: Matter and Its Interactions, PS7: Motion and Stability: Forces and Interactions, and PS8: Energy. The first three physical science core ideas answer two fundamental questions What is everything made of? And Why do things happen?

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That are not unlike questions that students themselves might ask. These core ideas can be applied to explain and predict a wide variety of phenomena that occur in people s everyday lives, such as the evaporation of a puddle of water, the transmission of sound, the digital storage and transmission of information, the tarnishing of metals, and photosynthesis. And because such explanations and predictions rely on a basic understanding of matter and energy, students abilities to conceive of the interactions of matter and energy are central to their science education. For this reason we have chosen to present the two subjects together, thereby ensuring a more coherent approach to the core ideas across all grades. Core Idea PS9: Waves and Their Applications in Technologies for Information TransferHow can one explain the structure, properties, and interactions of matter? The existence of atoms, now supported by evidence from modern instruments, was first postulated as a model that could explain both qualitative and quantitative observations about matter (e. G. , Brownian motion, ratios of reactants and products in chemical reactions). Matter can be understood in terms of the types of atoms present and the interactions both between and within them. The states (i. E. , solid, liquid, gas, or plasma), properties (e. , hardness, conductivity), and reactions (both physical and chemical) of matter can be described and predicted based on the types, interactions, and motions of the atoms within it. Chemical reactions, which underlie so many observed phenomena in living and nonliving systems alike, conserve the number of atoms of each type but change their arrangement into molecules. Nuclear reactions involve changes in the types of atomic nuclei present and are key to the energy release from the sun and the balance of isotopes in matter. While too small to be seen with visible light, atoms have substructures of their own.

They have a small central region or nucleus containing protons and neutrons surrounded by a larger region containing electrons. The number of protons in the atomic nucleus (atomic number) is the defining characteristic of each element different isotopes of the same element differ in the number of neutrons only. Despite the immense variation and number of substances, there are only some 655 different stable elements. Each element has characteristic chemical properties. The periodic table, a systematic representation of known elements, is organized horizontally by increasing atomic number and vertically by families of elements with related chemical properties. The development of the periodic table (which occurred well before atomic substructure was understood) was a major advance, as its patterns suggested and led to the identification of additional elements with particular properties. Moreover, the table s patterns are now recognized as related to the atom s outermost electron patterns, which play an important role in explaining chemical reactivity and bond formation, and the periodic table continues to be a useful way to organize this information. The substructure of atoms determines how they combine and rearrange to form all of the world s substances. Electrical attractions and repulsions between charged particles (i. , atomic nuclei and electrons) in matter explain the structure of atoms and the forces between atoms that cause them to form molecules (via chemical bonds), which range in size from two to thousands of atoms (e. , in biological molecules such as proteins). Atoms also combine due to these forces to form extended structures, such as crystals or metals. The varied properties (e. , hardness, conductivity) of the materials one encounters, both natural and manufactured, can be understood in terms of the atomic and molecular constituents present and the forces within and between them. Within matter, atoms and their constituents are constantly in motion. The arrangement and motion of atoms vary in characteristic ways, depending on the substance and its current state (e. , solid, liquid).

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Chemical composition, temperature, and pressure affect such arrangements and motions of atoms, as well as the ways in which they interact. Under a given set of conditions, the state and some properties (e. , density, elasticity, viscosity) are the same for different bulk quantities of a substance, whereas other properties (e. , volume, mass) provide measures of the size of the sample at hand. Materials can be characterized by their intensive measureable properties. Different materials with different properties are suited to different uses. , plastics, nanoparticles). Moreover, the modern explanation of how particular atoms influence the properties of materials or molecules is critical to understanding the physical and chemical functioning of biological systems. By the end of grade 7. Different kinds of matter exist (e. , wood, metal, water), and many of them can be either solid or liquid, depending on temperature. Matter can be described and classified by its observable properties (e. , visual, aural, textural), by its uses, and by whether it occurs naturally or is manufactured. Different properties are suited to different purposes. A great variety of objects can be built up from a small set of pieces (e. , blocks, construction sets). Objects or samples of a substance can be weighed, and their size can be described and measured.

(Boundary: volume is introduced only for liquid measure. )By the end of grade 8. All substances are made from some 655 different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms. Pure substances are made from a single type of atom or molecule each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it. Gases and liquids are made of molecules or inert atoms that are moving about relative to each other. In a liquid, the molecules are constantly in contact with each other in a gas, they are widely spaced except when they happen to collide. In a solid, atoms are closely spaced and vibrate in position but do notchange relative locations. Solids may be formed from molecules, or they may be extended structures with repeating subunits (e. , crystals). The changes of state that occur with variations in temperature or pressure can be described and predicted using these models of matter. (Boundary: Predictions here are qualitative, not quantitative. )By the end of grade 67. Each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons. The periodic table orders elements horizontally by the number of protons in the atom s nucleus and places those with similar chemical properties in columns.

The repeating patterns of this table reflect patterns of outer electron states. The structure and interactions of matter at the bulk scale are determined by electrical forces within and between atoms. Stable forms of matter are those in which the electric and magnetic field energy is minimized. A stable molecule has less energy, by an amount known as the binding energy, than the same set of atoms separated one must provide at least this energy in order to take the molecule apart. How do substances combine or change (react) to make new substances? How does one characterize and explain these reactions and make predictions about them? Many substances react chemically with other substances to form new substances with different properties. This change in properties results from the ways in which atoms from the original substances are combined and rearranged in the new substances. However, the total number of each type of atom is conserved (does not change) in any chemical process, and thus mass does not change either. The property of conservation can be used, along with knowledge of the chemical properties of particular elements, to describe and predict the outcomes of reactions. Changes in matter in which the molecules do not change, but their positions and their motion relative to each other do change also occur (e. , the forming of a solution, Understanding chemical reactions and the properties of elements is essential not only to the physical sciences but also is foundational knowledge for the life sciences and the earth and space sciences. A change of state). Such changes are generally easier to reverse (return to original conditions) than chemical changes. Collision theory provides a qualitative model for explaining the rates of chemical reactions. Higher rates occur at higher temperatures because atoms are typically moving faster and thus collisions are more frequent also, a larger fraction of the collisions have sufficient energy to initiate the process. Although a solution or a gas may have constant chemical composition that is, be in a steady state chemical reactions may be occurring within it that are dynamically balanced with reactions in opposite directions proceeding at equal rates.

Any chemical process involves a change in chemical bonds and the related bond energies and thus in the total chemical binding energy. This change is matched by a difference between the total kinetic energy of the set of reactant molecules before the collision and that of the set of product molecules after the collision (conservation of energy). Some reactions release energy (e.

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