Chapter 5 The Periodic Law

Chapter 5The Periodic Law

Patterns of the Periodic Table

Section 1

History of the Periodic Table

History

Atomic masses standardized in 1860

Mendeleev organized all known elements according to atomic mass and chemical and physical properties

History

Medeleev noticed a trend in physical/chemical properties

Trends were “periodic” which means there is a repeating pattern

History

Mendeleev left several empty spaces

Predicted that some elements were not discovered yet.

Scandium, Gallium, and Germanium

History

Mendeleev arranged elements by atomic mass

In 1911, Henry Moseley arranged elements by nuclear charge (proton or atomic number)

History

Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.

patterns repeat according to atomic number

Modern Periodic Table

About 40 more elements have been discovered or created since Mendeleev’s time

Noble Gases

Discovered in 1894 by Lord Rayleigh and Sir William Ramsay (Argon)

Very difficult to discover since they are not reactive (inert)

Helium was discovered to exist on the Sun in 1865, but thought not to exist on Earth. (discovered in 1895)

Noble Gases

Ramsay made a new group for Helium and Argon

1898 Ramsay discovered Krypton and Xenon

Radon discovered two years later by Dorn

S block elements Group 1 and 2

Highly reactive elements Usually found bonded to other

elements in nature (compounds)

Group 1 elements

Known as the alkali metals All have an ns1 outer electron

configuration Hydrogen, Lithium, Sodium,

Potassium, Rubidium, Cesium, Francium

Group 2 elements

Known as the alkaline earth metals ns2 valence electron configuration Less reactive than Group 1

elements Beryllium, Magnesium, Calcium,

Strontium, Barium, and Radium

Hydrogen and Helium

Exceptions Hydrogen’s properties do not

resemble the alkali metals (behaves like a metal under extremely high pressures)

Helium’s E.C. is 1s2, but it doesn’t act like a Group 2 (acts like noble gas)

The d-Block ElementsGroups 3-12

Known as transition metals Less reactive than alkali

metals/alkaline earth metals Some exist as free elements in

nature Palladium platinum and gold

P-Block ElementsGroups 13-18

Properties vary greatly Includes metals, metalloids, and

nonmetals Valence electrons are equal to

group number minus 10

Halogens

Group 17 elements Fluorine, Chlorine, Bromine, Iodine,

and Astatine valence configuration is ns2 np5

Most reactive non metals React vigorously with metals

F-block ElementsLanthanides and Actinides

Shiny metals Most are radioactive Elements above atomic number 92

(Uranium) are man made

Periodic Trends

Periodic Law

When elements are arranged in order of increasing atomic #, elements with similar properties appear at regular intervals.

Chemical Reactivity

Families Similar valence e- within a group

result in similar chemical properties

Chemical Reactivity Alkali Metals Alkaline Earth

Metals Transition Metals Halogens Noble Gases

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Atomic Radius Atomic Radius

Li

ArNe

KNa

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Atomic Radius Increases to the LEFT and DOWN

D. Atomic Radius

Why larger going down? Higher energy levels have larger orbitals Shielding - core e- block the attraction

between the nucleus and the valence e-

Why smaller to the right? Increased nuclear charge without additional

shielding pulls e- in tighter

D. Atomic Radius

First Ionization EnergyE. Ionization Energy

KNaLi

Ar

NeHe

First Ionization Energy Increases UP and to the RIGHT

E. Ionization Energy

Why opposite of atomic radius? In small atoms, e- are close to the nucleus where

the attraction is stronger

E. Ionization Energy

Successive Ionization Energies

Mg 1st I.E. 736 kJ

2nd I.E. 1,445 kJCore e- 3rd I.E. 7,730 kJ

Large jump in I.E. occurs when a CORE e- is removed.

E. Ionization Energy

Al 1st I.E. 577 kJ

2nd I.E. 1,815 kJ

3rd I.E. 2,740 kJCore e- 4th I.E.11,600 kJ

Successive Ionization Energies Large jump in I.E. occurs when a

CORE e- is removed.

E. Ionization Energy

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Which atom has the larger radius?

Be or Ba

Ca or Br

Ba

Ca

Examples

Which atom has the higher 1st I.E.?

N or Bi

Ba or Ne

N

Ne

Examples

Which particle has the larger radius?S or S2-

Al or Al3+

S2-

Al

Examples

Electron Affinity

Neutral atoms can also acquire electrons.

The energy change that occurs when an electron is acquired by a neutral atom is call the atoms electron affinity.

Electron affinity

Trend EA increases left to right EA decreases going down

Electronegativity

Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound.

Electronegativity

Tend to increase across each period (left to right)

Tend to decrease going down