Trends in the Periodic Table

The Periodic Table

• Dmitri Mendeleev (1834-1907) determined the properties of every known element at the time– Atomic Mass– Density– Colour– Melting Point– Boiling Point

The Periodic Table: Periods

• Mendeleev arranged the known elements in order of increasing atomic mass

• He found that the properties of the elements repeated at definite, or PERIODIC, intervals– Na has similar properties to Li and K

The Modern Periodic Table:Atomic Number

• In 1915, the Periodic Table was reorganized based on the element’s atomic structure

• Each element has an ATOMIC NUMBER, which is unique to each element

• The atomic number begins with H (1) in the upper-left hand corner, and moves from Left to Right

The Modern Periodic Table:Groups

• Vertical columns in the periodic table

• Chemical families• Elements in a group share

very similar properties• Numbered from 1-18• Elements in the same GROUP

have the same number of atomic SHELLS where VALENCE ELECTRONS (outer electrons) are held

1 2 3 4 3 2 1 0

Nonmetals

Metals

Metalloids

Elements are grouped based on specific properties:

MetalsMetals

Non-MetalsNon-Metals

MetalloidsMetalloids

The Modern Periodic Table: Characteristics of Groups

• The number of valence electrons in the elements is same in a group. • The atomic radii increase from top to bottom• Metallic Elements:

– Metallic character and chemical reactivity increase from top to bottom

• Non-Metallic Elements:– Metallic character and chemical reactivity decrease from top to bottom

Elements are ordered in the periodic table according to reactivity and atomic number:

Na and K react with Water

Na

K

Mg and Ca React with Hydrochloric Acid (Same Group)

Mg

Ca

F, Cl, I are gases

F

Cl

I

The Modern Periodic Table: Groups of Elements

3 4 5 6 7 8 9 10 11 12

13 14 15 16 17

1812

Group 1: Alkali Metals

• Very reactive metals that do not occur freely in nature (Cs, Fr the most reactive)

• Valence Electrons: One; ready to lose that one electron to bond with other elements.

• Properties: Malleable, ductile, good conductors of heat and electricity, softer than most metals

• Can explode if exposed to water.

Group 2: Alkaline Earth Metals

• Very reactive• Valence Electrons: 2; can bond

easily with other elements• Not found free in nature

Groups 3-12: Transition Metals

• Properties: Ductile, malleable, conduct electricity and heat

• Valence Electrons: present in more than one shell

• Iron, cobalt, and nickel are the only elements known to produce a magnetic field.

Groups 13-15: Other Metals

• Properties: Ductile and malleable, solid, high density, opaque

• Valence Electrons: present in their outer shell.

Metalloids

• Along the stair-step line that distinguishes metals from non-metals

• Al is an exception as it is classified as an “Other Metal”

• Properties: Similar to metals and non-metals

• Si and Ge are semi-conductors (can carry an electrical charge under special conditions; used in calculators and computers)

Group 14-16: Non-Metals

• Properties: Do not conduct electricity or heat very well, brittle, not malleable or ductile, no luster, do not reflect light

• Exist as gases (N, O) or solids (C, S)

Group 17: Halogens

• “Salt-former”, compounds containing halogens are called “salts”

• Valence Electrons: 7; will bond easily with Alkali Metals.

• Exist as solids (I, At), liquid (Br), and gas (F, Cl)

Group 18: Noble Gases

• Valence Electrons: 0; prevents gases from readily forming compounds

• Very stable because they have the maximum electrons in their outer shell

Rare Earth Elements

• Lanthanide and Actinide series (Group 3 and Period 6-7)

• One element of the lanthanide series and most of the elements in the actinide series are trans-uranium (synthetic or man-made)

Mendeleev’s Periodic Law

If the elements are arranged according

to their atomic mass, a pattern can be

seen in which similar properties occur

regularly