Atoms are made of a positively charged nucleus surrounded by negatively charged electrons. The nucleus is a tiny fraction of the volume of an atom but makes up almost all of its mass. The nucleus is composed of protons and neutrons which have roughly the same mass but differ in that protons are positively charged while neutrons have no electric charge.
Learning Goal 2
The number of protons in the nucleus determines what an atom's electron configuration can be and so defines the element. 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.
Learning Goal 3
Although neutrons have little effect on how an atom interacts with other atoms, the number of neutrons does affect the mass and stability of the nucleus. Isotopes of the same element have the same number of protons (and therefore of electrons) but differ in the number of neutrons.
Learning Goal 4
The nucleus of radioactive isotopes is unstable and spontaneously decays, emitting particles and/or wavelike radiation. It cannot be predicted exactly when, if ever, an unstable nucleus will decay, but a large group of identical nuclei decay at a predictable rate. This predictability of decay rate allows radioactivity to be used for estimating the age of materials that contain radioactive substances.
Learning Goal 5
Scientists continue to investigate atoms and have discovered even smaller constituents of which neutrons and protons are made.
Learning Goal 6
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.
Learning Goal 7a
Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns.
Learning Goal 7b
An enormous variety of biological, chemical, and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules.
Learning Goal 8
The configuration of atoms in a molecule determines the molecule's properties. Shapes are particularly important in how large molecules interact with others.
Learning Goal 9a
The rate of reactions among atoms and molecules depends on how often they encounter one another, which is affected by the concentration, pressure, and temperature of the reacting materials.
Learning Goal 9b
Some atoms and molecules are highly effective in encouraging the interaction of others.
Learning Goal 10
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.