Atomic Theory and Periodic Table Module Overview

Periodic Table Cakes Atoms, Molecules, and Elements…Oh My! No, these are not things to fear like lions, tigers, and bears. You know matter is all around you. In this module, you will be looking at the composition of matter as well as the number of elements that make up the world around us. As a chemistry student, you must also familiarize yourself with the periodic table. The periodic table is as essential as the alphabet is to learning the English language or plus/minus is for computing mathematical problems. You will be investigating the properties of atoms, the organization of the periodic table, and how to use the periodic table to predict the properties of elements. Atoms and how they interact with each other is chemistry. The more you understand chemistry, the better you will understand the world we live in.

Essential Questions

How does the atomic structure of an element determine its physical and chemical properties?
How does the composition of an element determine the element's placement on the periodic table?
What are the trends of the periodic table and how can they be used to predict the properties of elements?

Key Terms

Atom – a unit of matter, the smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons.
Proton – a subatomic particle with a positive charge located in the nucleus of an atom and has a mass of 1 amu (atomic mass units).
Neutron – a subatomic particle with a neutral charge located in the nucleus of an atom and has a mass of 1 amu (atomic mass units).
Electron – a subatomic particle with a negative charge located orbiting around the nucleus within the electron cloud and has a mass of 1/1840 amu (atomic mass units).
Atomic mass unit (amu) – the standard unit used for indicating mass on an atomic scale (a very small unit of mass). It is equivalent to 1/12 the mass of carbon-12.
Nucleus – the central part of the atom housing the protons and neutrons.
Electron cloud - the negatively charged space around the atom nucleus where the probable orbitals of electrons are.
Electron energy levels (electron shells) – a probable electron configuration based on the level of energy that an electron can have in an atom. Each energy level can hold a certain number of electrons. The first energy level, which is closest to the nucleus and has the lowest amount of energy, can hold only two electrons. Electrons with higher energy are found in energy levels farther from the nucleus.
Valence electrons - an electron located in the outermost shell (valence shell) of the atom, that can be transferred to or shared with another atom.
Octet Rule - a rule stating that atoms lose, gain, or share electrons in order to have 8 valence electrons.
Atomic number - the number of protons in an atomic nucleus.
Isotope - atoms that have the same number of protons but different numbers of neutrons.
Atomic Mass - the average mass of all the different isotopes that make up the element. The average is calculated using the relative abundance of isotopes in a naturally occurring element.
Mass Number – the mass of an isotope calculated by adding the number of protons and neutrons.
Periodic Table - a table of the chemical elements arranged in order of atomic number so that elements with similar chemical properties appear in vertical columns.
Metal – elements located on the left side of the periodic table that are solid at room temperature, have a shiny luster, the ability to conduct heat and electricity, can be hammered into thin sheets or drawn into wires, and can easily lose electrons in order to make positive ions.
Nonmetal - elements located on the right side of the periodic table that can exist in all 3 states (solids, liquids, gases) at room temperature, do not have the ability to conduct heat and electricity, are brittle, and can easily gain electrons in order to make negative ions or share electrons.
Metalloid – elements straddling the diagonal dividing line between boron and astatine that display both metallic and nonmetallic properties and are solid at room temperature.
Group (Family) – a vertical column on the periodic table. Elements in the same group (family) have the same number of valence electrons and therefore have similar physical and chemical properties.
Period – a horizontal row on the periodic table. Elements in the same period have the same number of total energy levels but do not have similar characteristics.
Alkali Metals – elements in Group 1 on the periodic table. These are very reactive metals, which readily lose their 1 valence electron to form ionic compounds with nonmetals.
Alkaline Earth Metals – elements in Group 2 on the periodic table. These are also reactive metals, although not as reactive as alkali metals.
Transition Metals - elements occupying a central block in the periodic table (Group 3 – 12). An incomplete inner electron shell, multiple valences, colored compounds, and the ability to form stable complex ions characterize these metals.
Halogens – elements in Group 17 on the periodic table. The term "halogen" means "salt former" because compounds containing halogens are called salts. These elements are very reactive nonmetals. Since they have 7 valence electrons, they readily gain 1 electron.
Noble Gases – elements in Group 18 on the periodic table. These nonmetals are considered stable, nonreactive inert gases because they have full valence shells.
Ion – an electrically charged atom due to losing or gaining 1 or more electrons.
Cation – a positively charged ion due to the loss of 1 or more electrons.
Anion – a negatively charged ion due to gaining 1 or more electrons.
Oxidation Number – numerical charge of an ion that indicates the number of electrons lost, gained, or shared. For example, a +1 means an atom lost 1 electron whereas a -3 means an atom gained 3 electrons.
Periodic Law - when elements are arranged in order of increasing atomic number, there is a periodic repetition of their chemical and physical properties.
Atomic radius - the atomic radius is a way of measuring the size of an atom.
Ionization energy - the energy required to remove the most loosely held electron from an atom in the gas phase. The higher the value of the ionization energy, the harder it is to remove that electron.
Electron affinity - electron affinity can be thought of as how much an element wants electrons.
Electronegativity - the tendency of atoms to attract electrons. The values of electronegativity are higher for elements that more strongly attract electrons.

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