The Periodic TableUnit 3/Chapters 3 & 8 Notes

Chemistry CPA

Unit Objectives:

• To describe the contribution of the structure of the periodic table by scientists such as Dobereiner, Mendeleev, and Mosley

• To describe the information given in an element square on the periodic table• To know the difference (in structure and properties) between families/groups and periods• To be able to distinguish between metals, nonmetals and metalloids and know their

general location on the periodic table• To describe the general physical and chemical properties of metals and nonmetals• To be able to name and identify the properties of the following families: Alkali metals,

alkaline earth metals, transition metals, boron family, carbon family, nitrogen family, oxygen family, halogens and noble gases

• To be able to analyze the major trends on the periodic table: atomic radius, ionization energy, electronegativity, and electron affinity, and reactivity

The History of the Periodic Table

Dobereiner’s Triads• In 1829, Johann Wolfgang Dobereiner, a German scientist, was the first to classify elements into groups based on John Dalton's postulates.• He grouped the elements with similar

chemical properties into clusters of three called 'Triads'. • The distinctive feature of a triad was

the atomic mass of the middle element.• When elements were arranged in

order of their increasing atomic mass, the atomic mass of the middle element was approximately the average of the other two elements of the triad.

Mendeleev

• In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table. • He grouped elements according to

their atomic mass, and as he did, he found that the families had similar chemical properties. • Blank spaces were left open to add

the new elements he predicted would occur.

Mendeleev’s Table

Mosely

• Later, Henri Moseley (England, 1887-1915) established that each elements has a unique atomic number, which is how the current periodic table is organized.

What’s in a square?

• Different periodic tables can include various bits of information, but usually:• atomic number• symbol• atomic mass• number of valence electrons• state of matter at room

temperature.

Organization of the periodic table – Families/Groups (columns)(notes)

• The vertical columns of the table are called groups or families. Element in the same group have similar but not identical characteristics• Numbered from 1 to 18. • Elements in the same group have the same number of outer shell electrons, and hence similar chemical properties.

Organization of the periodic table – Periods (columns)• The horizontal rows of the table are called periods.• Numbered from 1 to 7. • Each contains elements with electrons in the sameouter shell. • Elements do not have similar properties in the periods like Families do.

More on Families and Periods…

Families/Groups: • Columns of elements are called

groups or families. • Elements in each family have similar

but not identical properties.• For example, lithium (Li), sodium (Na),

potassium (K), and other members of family IA are all soft, white, shiny metals.• All elements in a family have the same

number of valence electrons.

Periods:• Each horizontal row of elements is

called a period.• The elements in a period are not

alike in properties.• In fact, the properties change greatly

across even given row.• The first element in a period is

always an extremely active solid. The last element in a period, is always an inactive gas.

Types of elements

• There are three main types of elements: metals, non metals and metalloids• 1. Metals appear on the left hand side

of the zig zag line that separates the periodic table• 2. Non metals appear on the right hand

side of the zig zag line that separates the periodic table• 3. Elements on either side of the zigzag

line have properties of both metals and non-metals. These elements are called metalloids.

Properties of Metals

• Most elements are metals. 88 elements to the left of the stairstep line are metals or metal like elements.• Left side of the periodic table• Positive valencies

Physical Properties of Metals

• Luster (shininess) • Good conductors of heat and

electricity • High density (heavy for their

size) • High melting point • Ductile (most metals can be

drawn out into thin wires) • Malleable (most metals can be

hammered into thin sheets)

Chemical Properties of Metals

• Easily lose electrons • Corrode easily. Corrosion is a

gradual wearing away. (Example: silver tarnishing and iron rusting)

Properties of Nonmetals

• Nonmetals are found to the right of the stairstep line. Their characteristics are opposite those of metals.

Sulfur

Physical Properties of non-Metals• No luster (dull appearance) • Poor conductor of heat and electricity • Brittle (breaks easily) • Not ductile • Not malleable • Low density • Low melting point

Chemical Properties of Nonmetals• Tend to gain electrons • Since metals tend to lose electrons and nonmetals tend to gain

electrons, metals and nonmetals like to form compounds with each other. These compounds are called ionic compounds. When two or more nonmetals bond with each other, they form a covalent compound.

Properties of Metalloids

• Metalloids (metal-like) have properties of both metals and non-metals.• They are solids that can be shiny

or dull.• They conduct heat and

electricity better than non-metals but not as well as metals.• They are ductile and malleable.