Development of the Periodic Table Mendeleev Constructed the first periodic table according to the similarities in each element’s properties - He arranged them in order of atomic masses - He left blank spaces in his periodic table because there were no known elements with the appropriate properties and masses.

Later Mosley rearranged the periodic table by atomic number The Modern Periodic Table Periodic Law: When elements are arranged in order of atomic number, there is a repetition of their physical and chemical properties

Groups or Families: vertical columns. Group numbers are indicated with a number and a letter A or B - Elements within a group have similar physical and chemical properties - Group A elements are the representative elements because they exhibit a wide range of chemical and physical properties

Metals → ← Nonmetals Where are things located on the Periodic Table? The light blue elements are semimetals

Properties of Metals: - They make up 80% of the elements - All metals except for one is a solid at room temperature - One the big periodic table solids are black, liquids are blue, and gases are red - They have a metallic luster - They are good conductors of electricity - They are malleable - They are ductile

Properties of Nonmetals - They lack luster - They are brittle - They are poor conductors of electricity (insulators) Properties of Semimetals - They have some of the characteristics of metals and some of nonmetals

Periodic Trends Atomic Radius: The distance from the center of the nucleus of an atom to the outer edge of that atom As you go to the left and down the periodic table the atomic radius tends to increase.

Why does the atomic radius decrease if we are adding another proton and electron when we move to the right? Think as the principle quantum energy level of an atom as an amount of space. - As you move down the periodic table you add more space and make the atomic radius larger - As you move from the left to the right there is the same energy level (amount of space) but we add another proton and electron - This makes more attraction between these particles and contracts the atom

Ionic Radius: The distance from the center of the nucleus of an ion to the outer edge of that ion - As you go to the right and down the periodic table the ionic radius tends to increase. - The parent atoms of positive ions are always larger than the ion. - Because an energy level is lost and the protons have an even greater pull on the electrons - The parent atoms of negative ions are always smaller than the ion because they gain electrons

Ionization Energy: the amount of energy required to remove the outermost electron - The higher the number the harder it is to take away an electron

Electronegativity (Electron Affinity): The attraction that an atom has for electrons. - This is the reason that atoms form bonds