THE PERIODIC TABLE

Physical Science

Chapter 5

ARRANGING THE ELEMENTS

Physical Science

Chapter 5.1

Objectives:1. Describe how Mendeleev arranged

elements in the first periodic table.

2. Explain how elements are arranged in the modern periodic table.

3. Compare metals, nonmetals, and metalloids based on their properties and on their location in the periodic table.

4. Describe the difference between a period and a group.

Discovering a Pattern In 1869, Russian chemist Dmitri

MendeleevArranged the elements in order of

increasing atomic mass. Periodic Properties of the

ElementsWhen the elements are arranged

in order of increasing atomic mass○ Those that had similar properties

occurred in a repeating pattern.○ These repeating patterns are

periodic, meaning that they happen at regular intervals.

Predicting Properties of Missing ElementsMendeleev’s arrangement had gaps in its pattern.

○ Mendeleev predicted that elements yet to be found would fill these gaps.

○ He also predicted the properties of the missing elements.By 1886, all of the gaps had been filled and Mendeleev’s

predictions were right.

Changing the Arrangement A few elements’ properties did not fit in the pattern of Mendeleev’s table. In 1914,

British scientist Henry Moseley found the number of protons—the atomic number—in an atom.

When the elements were arranged by atomic number, they fit the pattern in Mendeleev’s table.

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

Classes of Elements Elements are classified as:

MetalsNonmetalsMetalloids

The number of electrons in the outer energy levelOne characteristic that helps determine which

category an element belongs in. The zigzag line on the periodic table

Can help you recognize which elements belong in which category.

Metals: Found to the left of the zigzag line. Atoms of most metals have few electrons in

their outer energy level. All metals are

ShinyDuctileMalleableGood conductors of electric current and thermal

energy.

Nonmetals Found to the right of the zigzag line. Atoms of most nonmetals have an almost

complete set of electrons in their outer energy level.

Nonmetals are:Not shinyNot ductile, or malleablePoor conductors of electric current and thermal energy.

Metalloids The elements that border the zigzag line. Atoms of metalloids have about half of a

complete set of electrons in their outer energy level.

have some properties of metals and some properties of nonmetals.also called semiconductors

Decoding the Periodic Table Each Element is Identified

by a Chemical SymbolEach square on the periodic

table includes○ Element’s name○ Chemical symbol○ Atomic number○ Atomic mass.

For most elementsThe chemical symbol has one

or two letters.The newest elements have

temporary three-letter symbols.

6

C 12.011 Carbon

Atomic number

Chemical Symbol

Atomic Mass

Element Name

Horizontal rows Are Called Periods The chemical and physical properties of elements in a

row follow a repeating pattern as you move across the period.

Vertical columns Are Called GroupsElements in the same group often have similar

chemical and physical properties.

Group

Period