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
12
have the same number of
atomic SHELLS where
VALENCE ELECTRONS
(outer electrons) are held
343210
Elements are grouped based on specific properties:
Nonmetals
Metalloids
Metals
Metals
Non-Metals
Metalloids
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:
Mg and Ca React with
Hydrochloric Acid (Same
Group)
Na and K react with Water
Na
K
F, Cl, I are gases
F
Mg
Cl
Ca
I
The Modern Periodic Table:
Groups of Elements
1
18
2
13
3
4
5
6
7
8
9
10
11 12
14 15 16
17
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 transuranium (synthetic or man-made)
Mendeleev’s Periodic Law