The Periodic Table

The Periodic Table of The

Elements

Elements are like a collection

As more and more elements were

discovered it became more important to

organize and classify them

Between the late 1700’s and mid

1800’s scientists, using mostly atomic

spectroscopy, doubled the number of known elements.

In early 1800’s, German chemist J.W. Dobereiner observed that several of the elements could be

classified into groups of three which he

called triads

Ca, Sr, and Ba

Li, Na, K

Cl, Br, IDobereiner based his triads on similar

chemical properties

In addition:

Many of the properties of the middle element

in each triad are approximate averages of the properties of the first and third

element

Element Atomic DensityMass (amu)

Cl 35.5 1.56 g/LBr 79.9 3.12 g/LI 126.9 4.95 g/L

Ca 40.1 1.55 g/cm3

Sr 87.6 2.6 g/cm3

Ba 137 3.5 g/cm3

In 1865, English chemist J.A.R

Newlands presented another way to classify and

organize the 62 elements known at

the time

Newlands placed the elements in order of

increasing atomic mass

He noticed that the properties of the eighth element were like those of the first, the ninth

like those of the second, and so on….

He called this repeating pattern of every eight

elements

THE LAW OF OCTAVES

After the eight notes of the musical scale

Because he linked chemistry to music, he was not taken

seriously!

It took 20 years for him to

receive credit for recognizing

periodicity

In 1869 Russian Chemist Dimitri

Mendeleev and German chemist Lothar Meyer

published nearly identical ways of

classifying

But Mendeleev is generally more credited with the 1st periodic table for 2 reasons:

He published first

He was better at explaining it than

Meyer

Mendeleev also saw the “periods”

Credited with publishing the first

“periodic table”

Mendeleev got lots of credit because he left gaps for missing elements!

In 1913, English Chemist James

Moseley Presented a way of organizing the elements that

we still use today.

Moseley was the first to put the elements in order of increasing

Atomic #

Atomic # represents the

number of protons in the nucleus of

each element

When he did this, he saw the same

repeating periodic pattern, without the

exceptions that Mendeleev had to switch around

Periodic LawWhen the elements are arranged in

increasing order by their atomic

numbers, their properties repeat

periodically

The

Modern

Periodic Table

Each Square Tells about a different element

H Element Symbol

HydrogenElement Name

Not always there

1 Atomic NumberRepresents the number of PROTONS in each atom of

this element

1.009Atomic MassRepresents the number of PROTONS AND AVERAGE NUMBER OF NEUTRONS in each atom

of this element

H

Hydrogen

1

1.009

Atomic Number 1:

1 proton (positive charge particles) in

nucleus of EVERY hydrogen atom

Atomic Number 1:

ALSO means 1 electron (negatively charged particle)

OUTSIDE the nucleus

Atoms are NEUTRAL: Same number of positives as negatives

Atomic Mass of 1.009 means that there is an average of 1.009 PROTONS AND NEUTRONS

in the nucleus… Since there is

already 1 proton (AND THAT CAN NOT

CHANGE AND STILL BE HYDROGEN) That means

that the average atom of Hydrogen has

0 Neutrons!

He

Helium

2

4.003

Let’s do another4 Particles

2 MUST BE Protons

4-2 = 2 Neutrons in nucleus

Each block tells us about the element…

The periodic table arranges the

elements into rows and columns based on

similarities

Vertical columns are called groups.Vertical columns are called groups. Elements are placed in columns by Elements are placed in columns by

similar properties.similar properties. Also called familiesAlso called families

Alkali MetalsAlkali Metals

Group 1Group 1

ALL elements in Group 1 ALL elements in Group 1 have 1 electron in their have 1 electron in their outer regionouter region

Alkali Earth MetalsAlkali Earth Metals Group 2Group 2

ALL elements in Group 2 ALL elements in Group 2 have 2 electrons in their have 2 electrons in their outer regionouter region

Boron FamilyBoron Family

Group 13Group 13


Carbon FamilyCarbon Family

Group 14Group 14


Nitrogen FamilyNitrogen Family

Group 15Group 15


Oxygen FamilyOxygen Family

A.K.A. the ChalcogensA.K.A. the Chalcogens

Group 16Group 16


HalogensHalogens

Group 17Group 17


Noble GassesNoble Gasses

Group 18Group 18


Lanthanide SeriesLanthanide Series Actinide SeriesActinide Series

Horizontal rows are called “Periods”Horizontal rows are called “Periods” Each period also shows something Each period also shows something

in commonin common

Period 1Period 1 Each element has one region of Each element has one region of

space for electrons around itspace for electrons around it

Period 2Period 2 Each element in this period has two Each element in this period has two

regions of spaceregions of spacearound it for around it for electronselectrons

Period 3Period 3 Each element in this period has 3 Each element in this period has 3




The Lanthanides are part of period 6The Lanthanides are part of period 6



The Actinides are part of period 7The Actinides are part of period 7

The periodic table can also show larger “Groups”

METALS Non-METALS

METALLOIDS

Tall columns are collectively Tall columns are collectively referred to as the “representative referred to as the “representative elements”elements”

Short, center groups are collectively Short, center groups are collectively referred to as the “transition referred to as the “transition elements”elements”

Two long rows on bottom are Two long rows on bottom are collectively referred to as the “inner collectively referred to as the “inner transition metals”transition metals”

Periodic Trends

Atomic SizeAtomic Size First problem where do you start First problem where do you start

measuring.measuring. The electron cloud doesn’t have a The electron cloud doesn’t have a

definite edge.definite edge. They get around this by measuring They get around this by measuring

more than 1 atom at a time.more than 1 atom at a time.

Atomic SizeAtomic Size

Atomic Radius = half the distance between Atomic Radius = half the distance between two nuclei of a diatomic molecule.two nuclei of a diatomic molecule.

}Radius

Trends in Atomic Size Trends in Atomic Size

Influenced by two factors.Influenced by two factors. Energy LevelEnergy Level Higher energy level is further away.Higher energy level is further away. Charge on nucleusCharge on nucleus More charge pulls electrons in More charge pulls electrons in

closer.closer.

Group Group trendstrends

As we go down a As we go down a groupgroup

Each atom has Each atom has another energy another energy level,level,

So the atoms get So the atoms get bigger.bigger.

HLi

Na

K

Rb

Periodic TrendsPeriodic Trends As you go across a period the radius As you go across a period the radius

gets smaller.gets smaller. Same energy level.Same energy level. More nuclear charge.More nuclear charge. Outermost electrons are closer.Outermost electrons are closer.

Na Mg Al Si P S Cl Ar

The Periodic Table

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