Chapter 5: The Periodic TablePEPSRainier Jr/Sr High SchoolMr. Taylor

Section 1: Organizing the Elements Russian chemist Dmitri Mendeleev in

the 1860’s knew about 60 elements and their atomic masses.

When he placed these elements in order by atomic mass he saw that chemical properties repeated at regular intervals (periodic repetition).

Section 1: Organizing the Elements Mendeleev’s table had gaps in it but he

predicted the properties of these “gap” elements Predictions were close when these

elements were discovered.

Section 1: Organizing the Elements A few elements did not fit the pattern

Henry Moseley (English chemist) rearranged the elements by atomic number; problem solved.

The Periodic Law: when arranged by increasing atomic number, elements have similar chemical properties that repeat at regular intervals (periods).

Section 1: Organizing the Elements

Chemical symbol

Chemical name

Section 1: Organizing the Elements The rows are called periods

Elements become less metallic from left to right

The columns are called groups. Each column (group) has similar chemical

properties

Section 2: Exploring the Periodic Table The periodic repetition of chemical

properties is the result of the arrangement of electrons in the outer energy level (valence electrons).

Variations in physical properties are due to different atomic numbers (protons).

Section 2: Exploring the Periodic Table Elements are place in;

Rows by the number of electron energy levels

Columns by the number of electrons in the outer energy level (valence electrons).

Section 2: Exploring the Periodic Table Ion Formation

Atoms may gain or lose electrons to form ions

Ions are charged particles because they do not have the same number of protons and electrons (unbalanced charges).

Section 2: Exploring the Periodic Table Ion Formation

Atoms gain or lose electrons to achieve a full outer energy level.

Group 1; loses an electron easily, has a positive charge (cation).

Group 17; gain an electron easily, has a negative charge (anion)

Section 2: Exploring the Periodic Table Metals vs non-metals

Metals areShiny solids (mostly)Malleable (able to be hammered into

shapes)Ductile (can be stretched into wires)Conductors of electricity and heat

Section 2: Exploring the Periodic Table Metals vs non-metals

Non-metals areSolids, liquids, or gases at room

temp.Often dull and brittlePoor conductors of heat and

electricity (insulators)

Section 2: Exploring the Periodic Table Metals vs non-metals

SemiconductorsHave some properties of metals and

non-metalsAre used in computer chips

Section 3: Families of Elements Elements of a family have the same

number of valence electrons

Metals: left side of table Non-metals: right side of table

Section 3: Families of Elements Alkali metals: Group 1

One valence electron Form an ion with a 1+ charge HIGHLY reactive

Never found in Nature except combined with another element in a compound

Section 3: Families of Elements Alkaline Earth metals: Group 2

2 valence electrons Form a 2+ ion Very reactive, but less than Group 1

Section 3: Families of Elements Transition Metals

Number of valence electrons varies Some are reactive (iron), some are not

(Gold) Many metals we use everyday are in

this group (Iron, gold, aluminum, copper).

Section 3: Families of Elements Noble gases: Group 18

Full outer valence electron energy level

Non-reactive gases do not usually form compounds or molecules.

Section 3: Families of Elements Halogens: Group 17

7 electrons in outer energy level (almost full).

Gain 1 electron easily to fill the level; 1- charge

VERY reactive; combine easily with metals to form a salt (NaCl, KCl, SnF2).

Section 3: Families of Elements Other non-metals

Oxygen and Nitrogen are the most abundant gases in the atmosphere.

Carbon compounds form the basis of most of the molecules in living organisms.

Section 3: Families of Elements Semiconductors

Also called metalloids Silicon makes up 28% of the matter in

the Earth’s crust Sand is mostly silicon dioxide.