Chapter 5Chapter 5The Periodic LawThe Periodic Law

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History of the Periodic Table

1869 – Dmitri Mendeleev published his periodic table. He had arranged it by grouping together the elements that had

similar properties and by increasing atomic masses. His periodic table left empty spaces for new elements that would be discovered.

Mendeleev’s List of elements in Russian Circa 1869

Periodic Table circa 1898

History of the Periodic Table

1911 – Henry Moseley (a student of Ernest Rutherford) rearranged a few elements on the periodic table so that elements were

arranged by increasing atomic number rather than by atomic mass.

History of the Periodic Table

1944 – Glenn T. Seaborg rearranged the periodic table to make it look like it does today. He moved the Actinide Series and

the Lanthanide Series elements to the bottom of the periodic table.

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Modern Periodic Table

The Periodic Law

The physical and chemical properties of the elements are periodic functions of their atomic numbers

What are the trends among the elements for atomic radius?

The atomic radius of an element is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined.

– Atomic radii are often measured in picometers (pm).

1. Interpret Diagrams Which element in the figure above has the largest atomic radius?

1. Interpret Diagrams Which element in the figure above has the largest atomic radius?

Summary: trends in atomic radius

6. Compare If a halogen and an alkali metal are in the same period, which element will have the larger atomic radius?

6. Compare If a halogen and an alkali metal are in the same period, which element will have the larger atomic radius?

Group trends

Atomic radius increase as you move down because each atom has another energy level, so the atoms get bigger.

HLi

Na

K

Rb

Periodic Trends As you go across a period, the radius gets

smaller. Electrons are in same energy level. Increasing number of positive protons within

the nuclei pull on the valence electrons.

Na Mg Al Si P S Cl Ar

Learning Check

A Beryllium

B Magnesium

C Calcium

D Strontium

According to their positions on the Periodic Table, which of the following neutral atoms has the largest atomic radius?

CATIONS

Cations are positively charged ions Cations form by losing electrons. Cations are smaller than the atom they

come from. Metals form cations. Cations of representative elements

have noble gas configuration.

ANIONS Anions are negatively charged ions Anions form by gaining electrons. Anions are bigger than the atom they

come from. Nonmetals form anions. Anions of ‘main’ groups elements have

noble gas configuration.

Group trends

Adding energy level Ions get bigger as you

go down.

Li1+

Na1+

K1+

Rb1+

Cs1+

Ionic Radius A greater number of protons will cause an ion

to become smaller due to attractive forces between the nucleus and the valence electrons

greater number of electrons will cause an ion to become larger due to electron repulsion.

Li1+

Be2+

B3+

C4+

N3-O2- F1-

Period trends in ionic radius

Learning Check 2 Which of the following statements is true about the trend for

ionic radii? A When electrons are lost forming positive ions, the ionic

radius is larger than its corresponding neutral atom.

B When electrons are lost forming positive ions, the ionic radius is smaller than its corresponding neutral atom.

C When electrons are gained forming positive ions, the ionic radius is larger than its corresponding neutral atom.

D When electrons are gained forming positive ions, the ionic radius is smaller than it’s corresponding neutral atom.

What are the trends among the elements for ionization energy?

The energy required to remove an electron from an atom is called ionization energy.

– This energy is measured when an element is in its gaseous state.

– The energy required to remove the first electron from an atom is called the first ionization energy.

Ionization Energy Decreases as we move down the periodic table. The outermost energy level is farther from the nucleus.

Therefore, it is easier to remove an electron.

Ionization Energy– Increases as you move across the periodic table

– The nuclear charge(atomic #) increases across the period because you have more protons and your atomic radius is getting smaller. As a result, there is an increase in the attraction of the nucleus for an electron.

– The outermost electrons are just a little closer to the nucleus and so they are harder to remove.

Summary: trends in ionization energy

11. Compare Which element would have a larger first ionization energy: an alkali metal in Period 2 or an alkali metal in Period 4?

11. Compare Which element would have a larger first ionization energy: an alkali metal in Period 2 or an alkali metal in Period 4?

Learning Check

3 Which element in group 17 (group 7A), the halogens, has the highest ionization energy?

A Fluorine B Chlorine C Bromine D Iodine

Learning Check

4 Based on the periodic trend for ionization energy, which element in Period 3 has the greatest tendency to lose an electron?

A Sodium B Aluminum C Phosphorus D Argon

Atoms with large ionization energy values are

A. more likely to form positive ions

B. less likely to form positive ions

C. most likely to lose their outer electrons

D. lacking valence electrons

Electronegativity The tendency for an atom to attract

electrons to itself when it is chemically combined with another element.

High electronegativity means it pulls the electron toward it.

Electronegativity

The further down a group, the farther the electron is away, and the more electrons an atom has.

More willing to share. Low electronegativity.

Electronegativity

Metals let their electrons go easily resulting in a low electronegativity

Nonmetals want more electrons and take them away from others resulting in a high electronegativity.

ElectronegativityElectronegativity Values for Selected Elements

H2.1

He

0

Li1.0

Be1.5

B2.0

C2.5

N3.0

O3.5

F4.0

Ne

0

Na0.9

Mg1.2

Al1.5

Si1.8

P2.1

S2.5

Cl3.0

Ar

0

K0.8

Ca1.0

Ga1.6

Ge1.8

As2.0

Se2.4

Br2.8

Kr

0

Rb0.8

Sr1.0

In1.7

Sn1.8

Sb1.9

Te2.1

I2.5

Xe

0

Cs0.7

Ba0.9

Tl1.8

Pb1.9

Bi1.9

Learning Check Which diagram below correctly depicts the

increase in electronegativity across periods and down groups?

Summary: periodic trends

15. Explain Periodic Trends In general, how can the periodic trends exhibited by the elements be explained?

15. Explain Periodic Trends In general, how can the periodic trends exhibited by the elements be explained?

Reactivity Reactivity increases as you go

down the columns of metallic elements.

Reactivity decreases as you go down the columns of non-metallic elements.– Flourine is the most reactive

nonmetal

Valence Electrons The electrons available to be lost,

gained, or shared in the formation of compounds.

The electrons in the highest energy level

Label valence electrons on periodic table

Extra Slides

1+

H

Li

Na

Be

2+

Mg

B

3+

Al

C

4-4+

Si

N

3-

O

2-

F

1-

Ne

0

He

P S Cl

K

Rb

Cs

Fr

Ca

Sr

Ba

Ra

Ga

In

Tl

Ge

Sn

Pb

As Se

Ar

Br Kr

Sb Te I Xe

Bi Po At Rn