History of the Periodic Table Aristotle first classified the known elements into three groups Few elements, classified by physical characteristics Earths Gases Solids

Early 19 th century attempts at classification Dobereiner triads Newlands Law of octaves

Eight columns of repetitive properties Meyer arranged by atomic mass eight columns with elements of similar properties in the same column Mendeleev Eight columns similar to Meyer’s table, but saw inconsistencies and left spaces Meyer arranged by atomic mass eight columns with elements of similar properties in the same column Mendeleev Eight columns similar to Meyer’s table, but saw inconsistencies and left spaces

Current arrangement Moseley Determined the atomic number of the elements and arranged in order of atomic number rather than atomic mass Moseley Determined the atomic number of the elements and arranged in order of atomic number rather than atomic mass

Navigating the table Periods/Series These are the rows. When the elements are arranged in atomic number order, the properties of the elements repeat periodically – the periodic law Elements in the same period have the same number of energy levels, hence the same “n” quantum number Periods/Series These are the rows. When the elements are arranged in atomic number order, the properties of the elements repeat periodically – the periodic law Elements in the same period have the same number of energy levels, hence the same “n” quantum number

Navigating the table – cont. Groups or Families These are the columns The elements in a group or family have similar physical and chemical properties Groups or Families These are the columns The elements in a group or family have similar physical and chemical properties

Representative Elements Groups 1A through 7A and group 0 are the representative elements 1A are the alkali metals 2A are the alkaline earth metals Group 6A are the chalcogens Group 7A are the halogens Group 0 are the noble gases Groups 1A through 7A and group 0 are the representative elements 1A are the alkali metals 2A are the alkaline earth metals Group 6A are the chalcogens Group 7A are the halogens Group 0 are the noble gases

Metals The great majority of the elements are classified as metals. Metals have 3 or less electrons in the outer level, thus tend to form cations The metals with d sublevels filling are the transition metals The metals with f sublevels are the rare-earth elements 4f lanthanide series 5f actinide series The great majority of the elements are classified as metals. Metals have 3 or less electrons in the outer level, thus tend to form cations The metals with d sublevels filling are the transition metals The metals with f sublevels are the rare-earth elements 4f lanthanide series 5f actinide series

Nonmetals Nonmetals have 5 or more electrons in the outer level and tend to form anions

Metalloids Are located on the periodic table along the heavy stairstep line Metalloids exhibit some properties characteristic of metals and other properties characteristic of nonmetals Are located on the periodic table along the heavy stairstep line Metalloids exhibit some properties characteristic of metals and other properties characteristic of nonmetals

Periodic Trends Atomic Radius – the average size of the electron cloud Increases as you move down a group Decreases as you move from left to right across a period

Ionization energy The energy required to remove an electron from an atom Generally decreases as you move down a group For the representative elements generally increases as you move from left to right across a period This is due to the greater attraction of the nucleus for the electrons The energy required to remove an electron from an atom Generally decreases as you move down a group For the representative elements generally increases as you move from left to right across a period This is due to the greater attraction of the nucleus for the electrons

Electronegativity The tendency for the atoms of the element to attract electrons when they are chemically combined with atoms of another element Decreases as you move down a group Generally increases as you move from left to right across a period (excluding the noble gases) Trends in the transition metals are less regular The tendency for the atoms of the element to attract electrons when they are chemically combined with atoms of another element Decreases as you move down a group Generally increases as you move from left to right across a period (excluding the noble gases) Trends in the transition metals are less regular

Ionic Size Positive ions are always smaller than the neutral atoms from which they form Negative ions are always larger than the neutral atoms from which they form Positive ions are always smaller than the neutral atoms from which they form Negative ions are always larger than the neutral atoms from which they form