Chapter: The Periodic Table

Table of Contents

Section 1: Introduction to the

Periodic Table

What does periodic mean?

• Periodic means with a repeating

pattern

• A periodic event is predictable

Periodic Table

**Periodic Table is a table that shows all the

chemical elements that have been

discovered.

**The elements in the P.T. are arranged

according to their properties, in a repeating

pattern.

**This means that their properties can be

predicted, according to their position in the

P.T.

• https://www.youtube.com/watch?v=fPnw

BITSmgU

• The genius of Mendeleev's periodic

table

https://www.youtube.com/watch?v=oylT

OhzpJL4

• Mendeleev and The Modern Periodic

Table

Mendeleev

• Russian chemist that publish a version

of a P.T. in which the elements were

arranged according to their atomic

mass.

• He observed that this arrangement

revealed a pattern.

Importance of Mendeleev’s work:

The importance of Mendeleev’s work lies on the

periodic table repeating patterns that he

observed and described.

By analyzing the properties of different

elements already present in the PT, he could

infer the properties of elements that were not

discovered yet.

With time, these “missing” elements were

discovered and placed in the PT empty spots.

The repeating patterns allow scientists to:

1)make predictions about an element’s

chemical and physical properties, based on

this element’s position on the periodic table.

(Elements with similar properties are placed in

the same area of the periodic table)

1)Find the correct location of a new element

in the periodic table.

• Henry Moseley an English physicist realized that Mendeleev's table could be improved by arranging the elements according to atomic number ( number of protons in the nucleus of an atom) rather than atomic mass

• That’ how the Periodic Table is organized today

Atomic Mass X Atomic Number

A period is a row of elements in the periodic table whose properties change gradually and predictably.

Why????

Because the atomic number increases by one, when you move from one element to another.

There are seven periods

The organization of the PT - Textbook page 436

• The periodic table has 18 columns of elements and each one is called a group or family.

• The groups or families are the columns. A group contains elements that have similar physical or chemical properties.

Today’s Periodic table :

textbook page 435 – Zones on the

Periodic table

• PT is divided in different zones:

Representative Elements – Gr 1,2, 13 through

18

Transition Elements – Gr 3 through 12

Inner Transition Elements – Two rows placed

below

Each element has an element key

• Name of the element, symbol, atomic number, atomic mass, the state of matter (at room temperature), if they are synthetic or not.

• the color of the box will tell you the type of element ( metals, metalloids and nonmetals)

The Element Keys

Metals – nonmetals and Metalloids

in the PT – read page 438

Atoms X Elements

•Atoms are the building blocks of matter

•Atoms form elements (elements have one

type of atom only)

***Atoms have chemical and physical

properties that will be kept by the

elements

Properties of Atoms and the pattern or

trends in the periodic table

• The chemical and physical properties of

atoms change according to the

location of the atom in the periodic

table

• Some of the properties are: ionization

energy, electronegativity, reactivity,

atomic radius, melting and boiling

point…

Atomic radius – distance from the center

of the nucleus to the last energy level of

the electron cloud

Atomic radius = the size of the atom

Graphs will reflect the PT trend- GROUP 1 atomic

number increases and the radius increases

Properties of Atoms: Atomic Radius

The atomic radius = the size of the atom.

Atoms generally get smaller as you go across the periods

Graphs – reflect the PT trend - PERIOD 4

Atomic Number increases but radius decreases

How can we explain that the radius of the

atoms decreases, when the atomic

number increases?

We would imagine that the more electrons

an atom has, the bigger the radius would

be.

Explanation: open book page 467 – Models of

atoms

Look at Group 1: Atomic Number increases and

radius increases – number of electrons increases

but the electrons are not as packet – there is

more space that the atoms can occupy without

being packet. (more energy levels to fit the

electrons)

The circles represent energy levels - the area

where you find electrons

Explanation: open book page 467 – Models of

atoms

Period: Atomic number increases and radius

decreases

- number of electrons increases with the atomic

number, but the space available for the

electrons is the same ( 2 energy levels)

Ionization Energy

An ion is an atom that lost or received an

electron.

Ionization energy is also a property of the

atoms and shows a pattern in the P.T.

Properties of Atoms: Ionization Energy

• Ionization energy is the energy required

to remove an electron from an atom in

the gas state of matter, to form a

positive ion

• The higher the ionization energy,

the more difficult it is to remove an

electron, because the atom is very

stable.

Ionization Energy - Group 1

Ionization Energy- Period 4

Usually metals have high melting and boiling

points because the atoms are united by

strong bonds.

Reactivity

• It is another property and it is the capacity

of an atom, to react with another atom.

• Fluorine is the most reactive non-metal

• Francium is the most reactive of the

metals

• Helium is the least reactive element

• You can notice a pattern of reactivity in

the PT

Reactivity of Elements

Reactivity

• Why does the reactivity go UP when you

move down in Groups 1 and 2 (metals)

of the PT?

Reactivity of Group 1- alkali metals

Electrons are found

in the energy levels

of the atoms.

Lithium has 2

energy levels,

Sodium 3 and

Potassium 4.

Reactivity of Group 1- alkali metals

Going down the group

the reactivity increases

because:

-The atoms are bigger

and there are more

energy levels

- the electrons in the

outer energy level are

less attracted by the

positive nucleus and will

react easily when

compared to the ones

closer to the nucleus

Reactivity and

Electronegativity

• The elements that are very reactive,

also have a high electronegativity.

What is electronegativity?

IMPORTANT

When atoms combine forming molecules,

they can share, donate or receive

electrons, forming chemical bonds.

Electronegativity is another property

• It is the tendency of an atom to attract

the electrons of a bond when this atom

is in a molecule. Ex:

• The chlorine atom has a higher

electronegativity than the hydrogen atom, so

the bonding electrons will be closer to the Cl

than to the H in the molecule.

From left to right: atoms in a period have more

protons, so the + charge in the nucleus is stronger,

attracting more the electrons that will tend to stay

closer to the nucleus.