The Periodic Table

Periodic  The word periodic means “repeated pattern”.  Lunar Cycle  Days of the week  Months of the year  Seasons

Dmitri Mendeleev  A Russian chemist in the late 1800’s who looked for a way to organize the elements using a “periodic pattern”. Mendeleev organized his chart from lightest-to-heaviest elements and then used a repeating pattern based on the Physical & Chemical properties of the elements.

Period Table: Version 1.0 Looks Confusing!

Leave the empties!  Mendeleev had to leave some places in his chart blank because there where no known elements that fit into that spot.  Mendeleev predicted that there might be more elements that had not yet been discovered that could fit into those spots.  Once these predictions were made, other scientists started looking, and guess what?

Found it! Predicted Element Discovered Element NameEkasiliconGermanium Date Atomic mass Density (g/cm³) Melting point (°C)High947 ColorGray Predicted Element Discovered Element Name Ekaaluminium Gallium Date Atomic mass Density (g/cm³) Melting point (°C)Low29.78 ColorSilver Germanium was discovered by a ________ scientist. The prefix Eka mean close to or related to. Gallium was discovered by a ________ scientist.

There’s Always Room for Improvement  Every time a new element was discovered the periodic table would be updated. This is what is looks like today. Mendeleev’s Predicted Elements Every white slot represented a possible unknown elements, but Mendeleev did not have enough information to make predictions about the properties of these elements. Every empty green slot is a spot where Mendeleev predicted an unknown element would go.

Organizing the periodic table  Mendeleev organized elements by mass and chemical properties.  The Vertical columns are called groups, or families. These are elements that have similar chemical properties. The chemical properties of an atom are based on the number of electrons orbiting around the nucleus.

Organizing the periodic table  The first family or group called the alkali metals contains: Li, Na, K, Rb, Cs, Fr  These are dull grey, soft, metallic compounds that react violently with water. Disposal of Sodium Brainiac – Alkali Metals

Electron cloud structure  Not all electrons orbit at the same distance from the nucleus.  Each separate orbit is called an energy level or shell.  The 1 st orbital shell can only hold a maximum of 2 electrons. Hydrogen & Helium

More orbital shells  Once the 1 st shell is filled, we move on to a new orbital shell.  The second shell can hold a maximum of 8 electrons. Lithium Neon

Electron energy levels  Level 1 – 2 electrons  Level 2 – 8 electrons  Level 3 – 18 electrons  Level 4 – 32 electrons  Level 5 – 50 electrons

Let’s make this easier!  With the exception of the first energy level, all other elements repeat their chemical properties in a patter of 8’s We call this an Octave.  Every atom wants to be stable. This means getting as close to 8 electrons as possible in the outer shell. These electrons in the outer shell are called Valence electrons. Valence electrons are responsible for all chemical reactions between atoms.

Here’s the easy part  Instead of drawing pictures of the entire atom, we will ONLY draw the valence electrons.  We will use the chemical symbol for the atom and dots to represent the electrons.

4 rooms, 2 to a room.  Each group is labeled by the number of valence electrons in the outer electron shell.

This is the Lewis dot structure!  We will use the Lewis dot structure (a.k.a. – electron dot diagram) to help us figure out how elements interact with each other to do chemistry!  Let’s get in some practice!