The Periodic Table

1. The Periodic Table Organizing the Elements

2. Purpose of the Periodic Table • To organize the elements based on similar properties • Makes them easy to study, easy to predict patterns, easy to reference

3. Mendeleev • 1869, Russian scientist, Dmitri Mendeleev, saw hidden patterns in the elements . • Looked at similar chemical and physical properties. • Ex: silver and copper both tarnish in air • Fluorine and chlorine both toxic gases when breathed

4. First periodic table • Mendeleev wrote down all properties of the elements, including atomic mass and bonding power. • Atomic mass – average mass of one atom of the element. • Bonding power – number of chemical bonds an element can form.

5. First Periodic Table • Patterns appeared when the elements were arranged in order of increasing atomic mass. • Bonding power also changed in an orderly way. • Left blank spaces for elements he felt had not been discovered yet. Predicted their properties. • Periodic – regular, repeated pattern • Mendeleev published the 1st periodic table in 1869.

7. The Table and Atoms • What we know about atoms changed the periodic table • Atoms are made of protons and neutrons in the nucleus, electrons orbit the nucleus. • Atomic mass unit – the mass of one proton.

8. Atoms • AMU’s – used to measure the mass of atoms of the elements. • Example: Helium • Atomic mass = 4 • (2 protons, 2 neutrons) • Electrons have almost no mass • Neutral atom – means equal number of protons and electrons.

9. Atomic Number • Every atom of an element has the same number of protons. Defines that element. • Atomic number = # of protons • Table organized by atomic number

10. Trends in the Table

11. Trends in Table • Elements in a column are called a group, or family. Often given a family name. • Families have similar characteristics. • Ex: Alkali metals, 1st family – highly volatile, same atomic structure. • Horizontal rows – called periods.

12. Valence Electrons • Valence electrons – number of electrons in the outer layer around the nucleus • These electrons are responsible for bonding. • Determines the bonding power of an element. • Groups or families all have the same # of valence electrons.