Periodic Table Key

History of the Periodic Table

• Mendeleev: arranged elements in order of atomic mass, while grouping elements with similar properties in the same column. Predicted the existence of three new elements based on gaps in the Table

• Moseley: developed the concept of atomic number (equal to the number of protons) and the Table was reorganized in order of atomic number

The Periodic Law

• When elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic trend

– Groups or Families: elements with similar properties are arranged in vertical columns. These elements have similar valence electrons

– Periods: Horizontal Row – the row number is the same as the principal quantum number

Electron Configurations and the Periodic Table

• Valence Electrons: the atoms outermost electrons . These electrons occupy the highest principal energy level and are largely responsible for an atoms chemical properties

– The elements in a group have similar properties because they have valence electrons

– Bohr models show the valence electrons in the outer ring

Trends of the Periodic Table

1. Atomic Number

# increases from left to right & top to bottom

2. Atomic Mass

# increases from left to right & top to bottom

3. Atomic Radius

increases from top to bottom & right to left

4. Metal vs. Nonmetal

metals on left; nonmetals on right

Trends of the Periodic Table

• Chemical Activity

Metals – activity increases from top to bottom & right to left (Fr most active)

Nonmetals – activity increases from bottom to top & left to right (F most active)