CHAPTER 17SECTION 3

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

Name Ekasilicon Germanium

Date 1871 1886

Atomic mass 72 72.61

Density (g/cm³) 5.5 5.35

Melting point (°C) High 947

Color Gray Gray

 Predicted Element

Discovered Element

Name Ekaaluminium Gallium

Date 1871 1875

Atomic mass 68 69.72

Density (g/cm³) 6 5.904

Melting point (°C) Low 29.78

Color Silver Silver

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 ElementsEvery 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 1st orbital shell can only hold a maximum of 2 electrons.

Hydrogen &

Helium

More orbital shells

Once the 1st 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’sWe 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!