Alaska Science
Key Element A1

Performance Standard Level 4, Ages 15–18

Students develop, create and use models to demonstrate their understanding of the nature of particles and their interactions on the molecular, atomic and subatomic levels, and how these explain the physical and chemical properties of matter.

Sample Assessment Ideas

• Students experiment with puffed rice and a Van DeGraaf static electricity generator OR an “electric ferry” apparatus (styrofoam, tin cans, pencil, string, tack, electron source); build models to explain the observations using subatomic, atomic, molecular, and particulate structures.

• Students compare the viscosity of different oils, greases, petroleum and synthetic lubricants at different temperatures; build models to explain differences in properties.

Expanded Sample Assessment Idea

• Students examine samples of salt (NaCl) crystals and sugar crystals; prepare solutions and measure conductivity and freezing points; build models that exhibit differences at the subatomic, atomic and molecular level of organization and account for the differences in observations. [Proper SAFETY precautions should be used.]

Procedure

Students will:

1. Use a magnifying glass or microscope and hardness test device (e.g. scratch block) to observe and describe properties of salt and sugar crystals.

2. Prepare quantitative solutions of at least two different concentrations of salt in water (e.g. 0.1g per 100g water, and 2 g per 100 g water) and attempt to do the same using hexane instead of water.

3. Prepare quantitative solutions of at least two different concentrations of sugar in water (e.g. 0.1g per 100g water, and 2 g per 100 g water) and attempt to do the same using hexane instead of water.

4. Observe and compare the properties of the solutions using simple conductivity apparatus.

5. Observe and compare the freezing point of each solution and the freezing point of pure water and pure hexane.

6. Build models to represent the two different solids and the different solutions; models should include differences at the subatomic level (i.e. electrons and nucleus), atomic level (i.e. ions vs. covalent bonds) and the molecular level (i.e. polar vs. non-polar solvents).

7. Use the models to explain orally (or in writing) the difference between a solid and a solution.

Reflection and Revision

Use the models to explain how differences between the solid and their solutions leads to the observed differences in properties. Why do some solids dissolve in some liquids and not in others?

Levels of Performance

Standards Cross-References
( Alaska Department of Education & Early Development Standards)

National Science Education Standards

Matter is made of minute particles called atoms, and atoms are composed of even smaller components. These components have measurable properties, such as mass and electrical charge. Each atom has a positively charged nucleus surrounded by negatively charged electrons. The electric force between the nucleus and electrons holds the atoms together. (Page 178)

The atom’s nucleus is composed of protons and neutrons, which are much more massive than electrons. When an element has atoms that differ in the number of neutrons, these atoms are called different isotopes of the element. (Page 178)

The nuclear forces that hold the nucleus of an atom together, at nuclear distances, are usually stronger than the electric forces that would make it fly apart. Nuclear reactions convert a fraction of the mass of interacting particles into energy, and they can release much greater amounts of energy than atomic interactions. Fission is the splitting of a large nucleus into smaller pieces. Fusion is the joining of two nuclei at extremely high temperature and pressure, and is the process responsible for the energy of the sun and other stars. (Page 178)

Radioactive isotopes are unstable and undergo spontaneous nuclear reactions, emitting particles and/or wavelike radiation. The decay of any one nucleus cannot be predicted, but a large group of identical nuclei decay at a predictable rate. This predictability can be used to estimate the age of materials that contain radioactive isotopes. (Page 178)

Atoms interact with one another by transferring or sharing electrons that are furthest from the nucleus. These outer electrons govern the chemical properties of the element. (Page 178)

An element is composed of a single type of atom. When elements are listed in order according to the number of protons (called the atomic number), repeating patterns of physical and chemical properties identify families of elements with similar properties. This “Periodic Table” is a consequence of the repeating pattern of outermost electrons and their permitted energies. (Page 178)

Bonds between atoms are created when electrons are paired up by being transferred or shared. A substance composed of a single kind of atom is called an element. The atoms may be bonded together into molecules or crystalline solids. A compound is formed when two or more kinds of atoms bind together chemically. (Page 179)

The physical properties of compounds reflect the nature of the interactions among its molecules. These interactions are determined by the structure of the molecule, including the constituent atoms and the distances and angles between them. (Page 179)

Solids, liquids, and gases differ in the distances and angles between molecules or atoms and therefore the energy that binds them together. In solids the structure is nearly rigid; in liquids molecules or atoms move around each other but do not move apart; and in gases molecules or atoms move almost independently of each other and are mostly far apart. (Page 179)

Carbon atoms can bond to one another in chains, rings, and branching networks to form a variety of structures, including synthetic polymers, oils, and the large molecules essential to life. (Page 179)

Each kind of atom or molecule can gain or lose energy only in particular discrete amounts and thus can absorb and emit light only at wavelengths corresponding to these amounts. These wavelengths can be used to identify the substance. (Page 180)

Benchmarks

The usefulness of a model can be tested by comparing its predictions to actual observations in the real world. But a close match does not necessarily mean that the model is the only “true” model or the only one that would work. (Page 270)

A physical or mathematical model can be used to estimate the probability of real-world events. (Page 230)

Atoms are made of a positive nucleus surrounded by negative electrons. An atom’s electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons. (Page 80)

The nucleus, a tiny fraction of the volume of an atom, is composed of protons and neutrons, each almost two thousand times heavier than an electron. The number of positive protons in the nucleus determines what an atom’s electron configuration can be and so defines the element. In a neutral atom, the number of electrons equals the number of protons. But an atom may acquire an unbalanced charge by gaining or losing electrons. (Page 80)

Neutrons have a mass that is nearly identical to that of protons, but neutrons have no electric charge. Although neutrons have little effect on how an atom interacts with others, they do affect the mass and stability of the nucleus. Isotopes of the same element have the same number of protons (and therefore electrons) but differ in the number of neutrons. (Page 80)

Scientists continue to investigate atoms and have discovered even smaller constituents of which electrons, neutrons, and protons are made. (Page 80)

When elements are listed in order by the masses of their atoms, the same sequence of properties appears over and over again in the list. (Page 80)

Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns. An enormous variety of biological, chemical, and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules. (Page 80)

The configuration of atoms in a molecule determines the molecule’s properties. Shapes are particularly important in how large molecules interact with others. (Page 80)