Dmitri Mendeleev (1834 – 1907) listed elements in vertical columns in order of increasing atomic mass noticed recurrence of their physical and chemical properties arranged so most similar properties were side by side predicted properties of the missing elements

Henry Moseley ( ) 1 st scientist that set the table in order of atomic number. 1 st scientist that set the table in order of atomic number.

Modern Periodic Table Periods horizontal rows of the periodic table properties change from group to group Groups or Families vertical columns elements of any group have similar physical and chemical properties Representative elements – Group 1A - 7A and 0 (8A) exhibit a wide variety of physical and chemical properties

Modern Periodic Table Periodic Law When the elements are arranged in order of increasing atomic #, there is a periodic pattern in their physical and chemical properties

one half of the distance from center to center of two like atoms distance between centers of like atoms that are joined together in a diatomic molecule one half of the distance from center to center of two like atoms distance between centers of like atoms that are joined together in a diatomic molecule Atomic Radius

Group Trends increases as you go down a group Periodic Trends Decrease as you go across a period

How does the size of an atom change when electrons are added or removed? A positive ions become smaller because they have a stronger hold on the electrons pulling them closer to the nucleus (lose an electron) Positive Ion Size

How does the size of an atom change when electrons are added or removed? Negative Ion Size Negative ions become larger because the electrons are pulling away from the nucleus due to the electrons outnumbering the protons.

Ionization Energy energy needed to remove an electron from an atom Group Trends In general, decreases as we move down a group Periodic Trends In general, increases as we move across a period

First Ionization Energy

Electron Affinity Ability of an atom to attract and hold an extra electron The more negative the electron affinity, the easier an atom can take an extra electron Group Trends tends to decrease as you move down a group Periodic Trends values become more negative as you move across a period

Electron Affinity

Electronegativity Attract electrons to itself when it is chemically combined with another element Attract electrons to itself when it is chemically combined with another element Fluorine has the highest electronegativity value Fluorine has the highest electronegativity value Cesium has the lowest electronegativity value Cesium has the lowest electronegativity value Electronegativity correlates to an atom’s ionization energy and electron affinity Electronegativity correlates to an atom’s ionization energy and electron affinity

Periodic Trends of Electronegativity Group Trend decreases going down a group Periodic Trend increases going across a period