Page 1

Structure of atoms

teaching standard spatial concepts

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 atom together. 178 B (9-12)

atom, force, interaction, mass, measurement, nucleus, small, surround

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. 178 B (9-12)

composition, mass, nucleus, size

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. 178 B (9-12)

bond, distance, fission, force, nucleus, scatter, size

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. 178 B (9-12)

decay, emission, nucleus, radiation, rate, wave

Structure and properties of matter

teaching standard spatial concepts

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. 178 B (9-12)

atom, distance, interaction, nucleus, outer, share, structure, transfer

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. 178 B (9-12)

outer, pattern, representation, spatialization

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. 179 B (9-12)

atom, atomicity, bond, composition, crystalline, interaction, pairing

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. 179 B (9-12)

angle, composition, distance, interaction, spatial interaction, structure

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. 179 B (9-12)

angle, bond, distance, molecule, motion, movement, rigidity, separation

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. 179 B (9-12)

atom, bond, branching, chain, molecule, network, ring
Page 2

Biological evolution

teaching standard spatial concepts

The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms. 185 C (9-12)


Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life forms, as well as for the striking molecular similarities observed among the diverse species of living organisms. 185 C (9-12)

fossil, similarity

The millions of different species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors. 185 C (9-12)


Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification. 185 C (9-12)

classification, group, hierarchy, similarity

Interdependence of organisms

teaching standard spatial concepts

The atoms and molecules on the earth cycle among the living and nonliving components of the biosphere. 186 C (9-12)

atom, composition, cycle, interaction, molecule

Energy flows through ecosystems in one direction, from photosynthetic organisms to herbivores to carnivores and decomposers. 186 C (9-12)

direction, flow

Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years. 186 C (9-12)

ecosystem, environment, interrelationship, size, stability

Living organisms have the capacity to produce populations of infinite size, but environments and resources are finite. This fundamental tension has profound effects on the interactions between organisms. 186 C (9-12)

environment, finite, infinite, size

Human beings live within the world’s ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems will be irreversibly affected. 186 C (9-12)

atmospheric, destruction, ecosystem, fractal, growth, habitat, scale, stability

Matter, energy, and organization in living systems

teaching standard spatial concepts

All matter tends toward more disorganized states. Living systems require a continuous input of energy to maintain their chemical and physical organizations. With death, and the cessation of energy input, living systems rapidly disintegrate. 186 C (9-12)

disintegration, order, organization, site, state
Page 3

Conservation of energy and increase in disorder

teaching standard spatial concepts

The total energy of the universe is constant. Energy can be transferred by collisions in chemical and nuclear reactions, by light waves and other radiations, and in many other ways. However, it can never be destroyed. As these transfers occur, the matter involved becomes steadily less ordered. 180 B (9-12)

collision, order, radiation, spatial interaction, universe, wave

All energy can be considered to be either kinetic energy, which is the energy of motion; potential energy, which depends on relative position; or energy contained by a field, such as electromagnetic waves.

field, kinetic, motion, position, wave

Heat consists of random motion and the vibrations of atoms, molecules, and ions. The higher the temperature, the greater the atomic or molecular motion. 180 B (9-12)

atom, molecule, motion, vibration

Everything tends to become less organized and less orderly over time. Thus, in all energy transfers, the overall effect is that energy is spread out uniformly. Examples are the transfer of energy from hotter to cooler objects by conduction, radiation, or convection and the warming of our surroundings when we burn fuels. 180 B (9-12)

convection, distribution, order, organization, radiation, spread, transfer, uniform

Interactions of energy and matter

teaching standard spatial concepts

Waves, including sound and seismic waves, waves on water, and light waves, have energy and can transfer energy when they interact with matter. 180 B (9-12)

interaction, matter, seismicity, spatial interaction, wave

Electromagnetic waves result when a charged object is accelerated or decelerated. Electromagnetic waves include radio waves (the longest wavelength), microwaves, infrared radiation (radiant heat), visible light, ultraviolet radiation, x-rays, and gamma rays. The energy of electromagnetic waves is carried in packets whose magnitude is inversely proportional to the wavelength. 180 B (9-12)

acceleration, deceleration, packet, proportion, radiation, wave, wavelength

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. 180 B (9-12)

discrete, wave, wavelength

In some materials, such as metals, electrons flow easily, whereas in insulating materials such as glass they can hardly flow at all. Semiconducting materials have intermediate behavior. At low temperatures some materials become superconductors and offer no resistance to the flow of electrons. 181 B (9-12)

flow, insulation, resistance