THE PERIODIC TABLE

Chapter 4

HOW ARE ELEMENTS ORGANIZED?

Groups of elements share certain properties

PERIODIC PATTERN

Newlands (1865) – Arranged elements

according to increasing atomic mass

Properties repeated every 8 elements

Law of octaves

Dobereiner (early 1800s)

Groups of 3 elements have similar properties

Triads

MENDELEEV

First periodic table

63 known elements at the time

Mendeleev’s table contains gaps that unknown elements should fill

He predicted the properties of these unknown elements & gave them names

MOSELEY

Arranged elements according to atomic number

Erased the discrepancies in Mendeleev’s table

OTHER CONTRIBUTIONS

Seaborg – pulled out inner transition elements

to condense periodic table

Ramsey – discovered noble gases

PERIODIC LAW

Elements with similar properties appear at

regular intervals (when arranged by atomic #)

Valence electrons – outermost electrons in an

atom of an element

Electrons that participate in chemical reactions

with other atoms

GROUPS/FAMILIES & PERIODS

Group/family = vertical column on the periodic

table

Elements have similar chemical properties because

of same # of valence electrons

Period = horizontal row

Elements have same number of occupied energy

levels (i.e. energy level 2)

GROUPS AND PERIODS

THE PERIODIC TABLE

Main Group elements

Transition elements

Inner transition elements

METALS, NONMETALS, METALLOIDS

Metals – occupy the majority of the periodic table

Located to the left of the “staircase”

Lustrous, Malleable, Ductile, Conductors

Alloy = a solid or liquid mixture of 2 or more metals

Nonmetals – generally opposite properties of metals

Metalloids – have properties of both, located along the “staircase”

METALS, NONMETALS, METALLOIDS

TRANSITION METALS

d-block elements

Groups 3-12

Do NOT have identical outer electron

configurations

May lose different #’s of valence electrons

Good conductors, ductile, malleable

LANTHANIDE & ACTINIDE SERIES

f-block elements

Lanthanides – first row of inner transition

elements

Shiny metals, similar in reactivity to alkaline earth

metals

Actinides – second row

Radioactive

ns

1

ns

2

ns

2n

p1

ns

2n

p2

ns

2n

p3

ns

2n

p4

ns

2n

p5

ns

2n

p6

d1

d5

d1

0

4f

5f

Ground State Electron Configurations of the Elements

ALKALI METALS – GROUP 1A (GROUP 1)

React with water to make alkaline solutions

One valence electron = VERY reactive

Lose their 1 valence electron to achieve noble gas configuration (octet)

Soft texture, dull or shiny, good conductors

Group 1A Elements (ns1, n 2)

ALKALINE EARTH METALS – GROUP 2A (GROUP

2)

Highly reactive

2 valence electrons

Harder and have higher melting points than

alkali metals

Group 2A Elements (ns2, n 2)

COMMON GROUP ELEMENTS – 3A TO 5A

(GROUPS 13-15)

3, 4, or 5 valence electrons (depending on group)

Some metals, some metalloids, some nonmetals

Group 3A Elements (ns2np1, n 2)

Group 4A Elements (ns2np2, n 2)

Group 5A Elements (ns2np3, n 2)

CHALCOGENS – GROUP 6A (GROUP 16)

Oxygen group

6 valence electrons

Name means “ore former”

Nonmetals, metalloids, metals

Group 6A Elements (ns2np4, n 2)

HALOGENS – GROUP 7A (GROUP 17)

Highly reactive nonmetals

7 valence electrons (1 short of a noble gas

configuration)

Often react with alkali metals

“Salt maker”

Group 7A Elements (ns2np5, n 2)

NOBLE GASES – GROUP 8A (GROUP 18)

Inert = unreactive

8 valence electrons (full set); except He (2 e-)

HYDROGEN

Most common element in

the universe

1 electron

Extremely flammable

Reacts unlike any other

element

PERIODIC TRENDS

Predictable change in a particular direction

Reactivity of Alkali metals

Increases as you down the group

Reactivity of Halogens

Increases as you go up the group

IONIZATION ENERGY

Energy supplied to remove an electron

IE + X (g) X+(g) + e-

Filled n=1 shell

Filled n=2

shell

Filled n=3

shell Filled n=4 shell

Filled n=5

shell

Electron Shielding – outermost electrons

are not held as tightly to the nucleus due

to the inner electrons “shielding” them

General Trend in Ionization Energies

Increasing First Ionization Energy

Incre

asin

g F

irst Io

niz

atio

n E

ne

rgy

ATOMIC RADIUS

Atomic radius = ½ the distance from the center to the center of

2 like atoms that are bonded

Atomic Radii

ELECTRONEGATIVITY

Ability of an atom in a compound to attract

electrons

Fluorine has highest electronegativity value

ELECTRON AFFINITY

Electron affinity = energy change when a

neutral atom gains an electron

Cation is always smaller than atom from which it

is formed.

Anion is always larger than atom from which it is

formed.

ION SIZE

Comparison of Atomic Radii with Ionic Radii