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