Section 1: Structure of the Atom

• Scientific Shorthand

  • Scientists have developed their own shorthand for dealing with long, complicated names.

  • Chemical symbols consist of one capital letter or a capital letter plus one or two small letters.

  • Elements have been named in a variety of ways.

  • Because scientists worldwide use this system, everyone understands what the symbols mean.

• Atomic Components

  • Atom: the smallest piece of matter that still retains the property of the element.

    • The nucleus of the atom contains protons and neutrons that are composed of quarks. The proton has a positive charge and the neutron has no charge. A cloud of negatively charged electrons surrounds the nucleus of the atom.

  • Nucleus: a small, positively- charged center of the atom

  • Protons: particles with an electrical charge of 1+.

  • Neutrons: neutral particles that do not have an electrical charge.

  • Atoms of different elements differ in the number of protons they contain.

• Quarks - Even Smaller Particles

  • Scientists hypothesize that electrons are not composed of smaller particles and are one of the most basic types of particles.

  • Quarks: Smaller particles that make up Protons and neutrons.

  • The search for the composition of protons and neutrons is an ongoing effort.

  • To study quarks, scientists accelerate charged particles to tremendous speeds and then force them to collide with—or smash into—protons.

  • Bubble chambers can be used by scientists to study the tracks left by subatomic particles.

  • Scientists use inference to identify the subatomic particles and to reveal information about each particle’s inner structure.

  • The tracks of the sixth quark were hard to detect because only about one billionth of a percent of the proton collisions performed showed the presence of a sixth quark— typically referred to as the top quark.

• Models - Tools for Scientists

  • Scientists and engineers use models to represent things that are difficult to visualize—or picture in your mind.

  • Scaled-down models allow you to see either something too large to see all at once, or something that has not been built yet.

  • Scaled-up models are often used to visualize things that are too small to see.

  • For the model to be useful, it must support all of the information that is known about matter and the behavior of atoms.

  • Electron Cloud: the area around the nucleus of an atom where its electrons are most likely found.

    • The electron cloud is 100,000 times larger than the diameter of the nucleus.

    • Because an electron’s mass is small and the electron is moving so quickly around the nucleus, it is impossible to describe its exact location in an atom.

Section 2: Masses of Atoms

• Atomic Mass

  • The nucleus contains most of the mass of the atom because protons and neutrons are far more massive than electrons.

  • The unit of measurement used for atomic particles is the atomic mass unit (amu).

  • The atomic mass unit is defined as one-twelfth the mass of a carbon atom containing six protons and six neutrons.

  • The number of protons tells you what type of atom you have and vice versa.

  • Atomic Number: The number of protons in an atom is equal to a number

  • Mass Number: The sum of the number of protons and the number of neutrons in the nucleus of an atom.

    • If you know the mass number and the atomic number of an atom, you can calculate the number of neutrons.

  • Atoms of the same element with different numbers of neutrons can have different properties.

• Isotopes: Atoms of the same element that have different numbers of neutrons.

  • You use the name of the element followed by the mass number of the isotope to identify each isotope.

  • Because most elements have more than one isotope, each element has an average atomic mass.

  • Average Atomic Mass: the weighted-average mass of the mixture of its isotopes.

Section 3: The Periodic Table

• Organizing the Elements

  • On a clear evening, you can see one of the various phases of the Moon.

  • Each month, the Moon seems to grow larger, then smaller, in a repeating pattern.

  • Chemical properties found in lighter elements could be shown to repeat in heavier elements.

  • Periodic Table: the elements are arranged by increasing atomic number and by changes in physical and chemical properties.

  • Mendeleev had to leave blank spaces in his periodic table to keep the elements properly lined up according to their chemical properties.

• The Atom and the Periodic Table

  • Objects often are sorted or grouped according to the properties they have in common.

  • Groups: families

  • Elements in each group have similar properties.

  • In a neutral atom, the number of electrons is equal to the number of protons.

  • Scientists have found that electrons within the electron cloud have different amounts of energy.

    • Scientists model the energy differences of the electrons by placing the electrons in energy levels

    • Energy levels in atoms can be represented by a flight of stairs. Each stair step away from the nucleus represents an increase in the amount of energy within the electrons. The higher energy levels contain more electrons.

  • Elements that are in the same group have the same number of electrons in their outer energy level. It is the number of electrons in the outer energy level that determines the chemical properties of the element

  • Energy levels are named using numbers one to seven.

    • Energy level one can contain a maximum of two electrons.

    • Energy level two can contain a maximum of eight electrons.

    • In elements in periods three and higher, additional electrons can be added to inner energy levels although the outer energy level contains only eight electrons.

  • The first row has hydrogen with one electron and helium with two electrons both in energy level one.

  • The second row begins with lithium, which has three electrons—two in energy level one and one in energy level two.

  • The row ends with argon, which has a full outer energy level of eight electrons.

  • Elements that are in the same group have the same number of electrons in their outer energy level.

  • Electron Dot Diagram: uses the symbol of the element and dots to represent the electrons in the outer energy level.

    • Electron dot diagrams are used also to show how the electrons in the outer energy level are bonded when elements combine to form compounds.

  • Since all of the members of a group on the periodic table have the same number of electrons in their outer energy level, group members will undergo chemical reactions in similar ways.

  • A common property of the halogens is the ability to form compounds readily with elements in Group 1.

  • Not all elements will combine readily with other elements.

• Regions on the Periodic Table

  • Periods: The horizontal rows of elements on the periodic table.

  • Most metals exist as solids at room temperature.

  • Most nonmetals are gases, are brittle, and are poor conductors of heat and electricity at room temperature.

  • Metalloids are located along the green stair-step line. Metals are located to the left of the metalloids. Nonmetals are located to the right of the metalloids.

• Elements in the Universe

  • Using the technology that is available today, scientists are finding the same elements throughout the universe.

  • Atoms join together within stars to produce elements with atomic numbers greater than 1 or 2—the atomic numbers of hydrogen and helium.

  • Scientists think that some elements are found in nature only within stars.

  • Promethium, technetium, and elements with an atomic number above 92 are rare or are not found on Earth.