elements remember: atoms of one type form an element elements are the simplest form of a substance...

ELEMENTS

Remember:

• Atoms of one type form an element

• Elements are the simplest form of a substance

• Every element is unique and has its own chemical and physical properties

Dimitri Mendeleev• Russian chemist who

worked in the mid 1800’s

• Researched the 63 known elements

• Made cards for each element with all the facts he could find

• Developed the first periodic table by atomic mass

• Not perfect!!

Henry Moseley• British scientist who

determined atomic numbers for the elements

• When elements arranged by atomic number and properties every element fell in place perfectly

• Periodic Law: Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups.

Elements are arranged:

Vertically into Groups

Horizontally Into Periods

Why?

If you looked at one atom of every element in a group you would

see…

Each atom has the same number of electrons in it’s outermost shell.

• An example…

The group 2 atoms all have 2 electrons in their outer shells

Be (Beryllium)

Atom

Mg (Magnesium) Atom

• The number of outer or “valence” electrons in an atom effects the way an atom joins with other atoms.

• The way atoms join determine many properties of the element.

• This is why elements within a group usually have similar properties.

If you looked at an atom from each element in a period

you would see…

Each atom has the same number of electron holding shells.

An example…

The period 4 atoms each have 4 electron containing shells

K (Potassium)

AtomFe (Iron) Atom

Kr (Krypton)

Atom

4th Shell

Each group has distinct properties

• The periodic Table is divided into several groups based on the properties of different atoms.

Alkali Metals

Soft, silvery colored metals

Very reactive especially with water

Not found in pure form in nature

Alkaline Earth Metals

Silvery-White Metals

Fairly reactive

Many are found in rocks in the earth’s crust

Transition Metals

Malleable (easily bent/hammered into wires or sheets)

Most are good Conductors of electricity

How many things can you think of that have Transition Metals in

them?

Metalloids lie on either side of the “stairstep” line

They share properties with both metals and non-metals

Si (Silicon) and Ge (Germanium) are very important “semi-conductors”

Where are semiconductors used?

Nonmetals

Brittle

Do not conduct electricity

Groups 13-16

Group 13Boron Group

Group 14Carbon Group

Group 15Nitrogen Group

Group 16 Oxygen Group

Most are poisonous

Fairly reactive

Halogens

Chlorine Gas was used as a chemical weapon during World War I.

It was used by the Nazis in World War II.

Non-reactive

Gases at room temperature

Very Stable

Noble Gases

WHY STABLE?

Noble gases have full valence levels!

Actinide Series

•Share properties of Group 3 transition metals•Rare and some are radioactive•Elements with atomic numbers greater than 92 (Uranium) are synthetic.Lanthanide Series