Periodic Table

The Periodic Table

Lesson 3

Why is part of the periodic table separate
and below the rest of it?

Focus Question

electron dot diagram

group

period

periodic table

New Vocabulary

chemical property: any characteristic of a
substance that indicates whether it can undergo
a certain chemical change

Review Vocabulary

What do you see in this picture

Periodic

​Alef 42. Organizing the Elements

Home

Open in new tab

Copy link

In the late 1800s, a Russian chemist named Dmitri
Mendeleev presented a way to organize
all the known elements.
•

He arranged elements in rows based on increasing
atomic mass.

•

He arranged elements in columns based on
elements that shared similar physical and chemical
properties.

•

He left blank spaces and predicted properties for
elements not yet discovered.

Organizing the Elements

Mendeleev’s Predictions

Predicted Properties of
Ekasilicon (Es)

Actual Properties of
Germanium (Ge)

Existence predicted:1871

Actual Discovery:1886

Atomic mass= 72

Atomic mass=72.61

High melting point

Melting point=938oC

Density=5.5g/cm3

Density=5.323 g/cm3

Dark gray metal

Gray metal

Density of EsO2=4.7g/cm3

Density of GeO2=4.23g/cm3

Scientists later confirmed the identities of the missing elements and found
that their properties were similar to what Mendeleev had suggested.

In the modern periodic table, the elements are
arranged by increasing atomic number—not
atomic mass—and by periodic changes in
physical and chemical properties.

Organizing the Elements

Changes in Periodic table

Increasing

atomic mass

Changes in Periodic table

In 1913, A young English scientist named Henry G.J Moseley arranged all the
known elements based on increasing atomic number ( the number of protons).

This new arrangement seemed to solve the problem of fluctuating mass.

Increasing

atomic number

Multiple Choice

What was Henry Moseley’s improvement to the periodic table?

• He arranged elements by atomic mass.

• He arranged elements by atomic number.

• He placed elements with similar properties in columns.

• He placed elements with similar properties in rows.

•

The modern periodic table consists of boxes,
each containing information such as element
name, symbol, atomic number, and atomic
mass.

•

The horizontal rows of elements in the
periodic table are called periods and are
numbered 1 through 7.

•

The vertical columns in the periodic table are
called groups (also called families), and they
are numbered 1 through 18.

The Atom and the Periodic Table

Home

Open in new tab

Copy link

Home

Open in new tab

Copy link

Knowing in which region an element is located
allows you to know its likely properties.

Regions of the Periodic Table

Home

Open in new tab

Copy link

Scientists have discovered that electrons within an
electron cloud have different amounts of energy.
Scientists model the energy differences between
electrons by placing electrons in energy levels.

Electron cloud structure

Step 1=less energy
Step4=more energy

Multiple Choice

How many more electrons can energy level 4 hold than energy level 3?

• 14

• 18

• 32

• 50

Electron cloud structure

Electron cloud structure

Elements in the same group have the same number of electrons in their outermost energy
(valence electrons) which determines the chemical properties of each individual element.

Electron cloud structure

Energy levels coincide with the number of rows on the periodic table. ( 1 to 7 )

1

2

3

An electron dot diagram
consists of the chemical
symbol of an element
surrounded by dots to
represent the number of
electrons in the outermost
energy level. Elements in the
same group have the same
number of electrons in their
outermost energy levels.

The Atom and the Periodic Table

The Atom and the Periodic Table

Home

Open in new tab

Copy link

An electron dot diagram can provide
information about how an atom might react,
the substance it could form, and why an atom
might be nonreactive.

The Atom and the Periodic Table

Multiple Choice

What can you determine about this element from its electron dot diagram?

• It is from group 1 and is reactive.

• It is from group 18 and is reactive.

• It is from group 1 and is unreactive.

• It is from group 18 and is unreactive.

Home

Open in new tab

Copy link

New Elements

Scientists around the world continue their research into the synthesis elements.

Elements

Roentgenium (Rg)

Element 111 officially approved
in 2004

Copernicium (Cn)

Element 112 in 2010

Scientists have synthesized elements 113 through 118.
The search for elements with higher atomic numbers continues.

These elements are produced in the laboratory by joining smaller atom into a
single larger atom.

•

Many of the same elements are found
throughout the universe.

•

Many scientists think that hydrogen and helium
are the building blocks of all other elements.

•

Atoms fuse within stars to produce heavier
elements with atomic numbers greater than
hydrogen and helium.

Elements in the Universe

Multiple Choice

Which best describes magnesium based on its location ?

• It’s a metal and is likely shiny

• It’s a nonmetal and is likely shiny.

• It’s a metal and is likely a gas.

• It’s a nonmetal and is likely a gas.

Home

Open in new tab

Copy link

Home

Open in new tab

Copy link

Multiple Choice

Which statement correctly describes the periodic table?

• Elements in a group have similar properties but different numbers of outermost electrons.

• Elements in a period have similar properties but different numbers of outermost electrons.

• Elements in a group have similar properties and the same number of outermost electrons.

• Elements in a period have similar properties and the same number of outermost electrons.