Structure of the Periodic Table
1. Dmitri Mendeleev determined that there was a regular, repeating pattern (periodic) to the properties of the elements and arranged them in order of increasing atomic mass. Father of the Periodic Table
2. Henry Moseley determined the number of protons (atomic number) in an atom and found that when he arranged the elements by atomic number, every element fell into its proper place in an improved periodic table.
Periodic Table of the Elements
· The zigzag line on the table helps to identify the metals, nonmetals, and metalloids.
o Most elements are metals and are found to the left of the zigzag line.
§ Metals are shiny, good conductors, ductile (can be drawn into thin wires), and malleable (flattened with a hammer without shattering).
o Nonmetals are found to the right of the zigzag line.
§ Nonmetals are dull, poor conductors, and brittle.
o Metalloids border the zigzag line.
§ Metalloids are called semiconductors, and have some properties of metals and nonmetals.
· Each square on the periodic table contains information about an element.
o The atomic number determines the identity of the element, and is the number of protons in the nucleus of the atom.
o The atomic mass is the sum of the atoms’ neutrons and protons.
· An atom is neutral (no charge) when there are equal numbers of protons (+) and electrons (-).
· When an atom gains or loses electrons, the protons ≠ electrons, and the atom is considered an ion.
o When the atom gains electrons, the atom is negatively charged because there are more electrons than protons.
o When the atom loses electrons, the atom is positively charged because there are more protons than electrons.
· When the number of neutrons in the atom changes, it is an isotope.
· Each horizontal row of elements (from left to right) is called a period. Elements in the same period have the same number of electron shells.
· Each column of elements (from top to bottom) is called a group and have the same number of valence electrons (electrons in their outer shell). Elements in the same group often have similar chemical and physical properties, and the group is also referred to a “family”.
· The groups are:
o Group 1 – Alkali Metals. These are the most reactive of the metals. Reactive meaning elements whose atoms will take, give, or share electrons with other atoms in order to have a complete set of electrons in the valence shell.
o Group 2 – Alkaline-Earth Metals.
o Groups 3 – 12 – Transition Metals. These include the lanthanides and actinides located below the periodic table. They are placed at the bottom because the periodic table would become too wide if they were not placed there.
o Groups 13 – 16 – referred to as the “BCNO” Group. “BCNO” refers to the name of the element at the top of each column: Boron, Carbon, Nitrogen, and Oxygen.
o Group 17 – Halogens. These are the most reactive nonmetals.
o Group 18 – Noble Gases. These are unreactive nonmetals because the noble gases have a complete set of electrons in their outer shell.
o Hydrogen – the most abundant element in the universe. Its properties do not match any single group, so it is set apart from the other elements in the table. It is placed above Group 1 because it has only one electron in its outer shell.