Chapter 6: The Periodic Table

Chapter summary6:1 History od the Periodic table

1) Mendeleev’s Periodic table2) Problems with early periodic tables

6:2 Modern Periodic table1) Key points: Periodic law, Periods and Groups, 3 broad classes of elements2) Properties of the 3 classes of elements (Metals, nonmetals and metalloids)3) Sorting elements based on general properties (3-types)4) Sorting elements based on electron configuration (4-types)5) Periodic trends:

a) Atomic sizeb) Ionization energyc) Ionic sized) Electronegativity Chemistry _ Notes

Dr. Chirie Sumanasekera10 /30/ 2017

6.1: History of the periodic table1) Mendeleev’s Periodic table2) Problems with early periodic tables

History: Mendeleev’s periodic table

• For thousands of years only a few elements were known - Gold, Silver and copper

• As chemists began using the scientific method, the rate of discovery of elements increased

• Chemists used the properties of elements to sort them into groups.

• In 1869 Dimitri Mendeleev organized the known elements into groups based on repeating properties and increasing atomic mass

• Mendeleev left spaces for elements still not discovered (?) as he predicted their properties and discovery

• In the late 1800s Gallium & Germanium which has properties similar to Mendeleev’s predictions for elements between Zn and As were discovered. Then his periodic table gained acceptance.

Mendeleev’s published periodic table from 1869

History: Problems with early periodic tables

• When Mendeleev created his periodic table, scientists did not know about a) the structure of the atom or b) that atoms of each element had a unique number of protons (atomic

number)• Number of protons is the same in all isotopes of an element. Proton numbers are

different only between different elements

• So arranging elements based on atomic mass- the sum of protons and neutrons-is not a good way to arrange elements based on their properties as it ignores the elements with chemically similar isotopes

• A better way to groups elements is by Atomic number – which is unique to each element.

6.2: The Modern Periodic Table

Modern Periodic Table: Organization of Elements

Group:1234567891011121314 15161718

Period:1

2

3

4

5

6

7

Metals Metalloids Nonmetals

Figure 6.5 (p:158)

1) Key Points on the arrangement of Elements:1) Arranged in order of increasing atomic number (protons)

2) 7 periods and 18 groups /columns

3) Each period represents a Principle Energy Level (n=1 to n=7)

4) More elements in higher numbered periods because there are more orbitals in those energy levels

5) Elements within a group have similar properties

6) Properties of elements in a period change as you go from left to right but the properties within a period repeat as you move from one to another period

7) Three broad classes of elements: majority of the elements are metals (left side), some are nonmetals (upper right) and in between these are a few metalloids

8) Across a period elements become less metallic• Periodic law: When elements are arranged in order f increasing atomic number

there is a periodic repetition of their physical and chemical properties

2) properties of the3 classes of Elements

*Noble gases: He, Ne, Ar, Kr, Xe, Rn**Ductile = make into wires Malleable = can be hammered into shape

1.Metals 2.Metalloids 3.Nonmetals

Percentofelements 80% 6% 14%

Heatconduction Excellent poor Mostlyverypoor

Electricalconduction Excellent Poor(siliconchipsmadeofmixturesofSiandBconductwell)

Mostly verypoor

At roomTemperature: AllSolid (exceptHg) All solid Somearesolid,gas(H,He,N,O,F,Clandallnoblegases*)andBr isabrownliquid

**Ductileandmalleable yes no no

Highluster/sheen Yes no Notreally

Toughness Usuallyhard soft Rangefromhardtosoft

Ingeneral: All havesimilarproperties

Hasbothmetalandnonmetalproperties

HastheoppositepropertiesofMetalsandthisgrouphasgreatvariation inproperties