The Periodic Table

download report

Transcript The Periodic Table

The Periodic Table

Section 1

- Organizing the Elements

Section 2

- Exploring the Periodic Table

Section 3

- Families of Elements

State Standards

• • • CLE 3202.1.3 Characterize and classify elements based on their atomic structure CLE 3202.Inq.1 Recognize that science is a progressive endeavor that reevaluates and extends what is already accepted CLE 3202.Inq.6 Communicate and defend scientific findings

1 - Organizing The Elements

• KEY QUESTIONS : • How did Mendeleev arrange the elements in his periodic table?

• How are elements arranged in the modern periodic table?

Mendeleev - Recognizing Patterns

• By 1860, 60 + elements were known • Dmitri Mendeleev, Russian Chemist, studied properties of the elements • 1869 : he published first Periodic Table of Elements • Arranged by rows of increasing mass number • If chemical properties repeated, new row started – EXAMPLE : Lithium and Sodium are very reactive – Gold and Silver have similar properties, same column

Predicting New Elements

• • • Gaps existed in his table ?

Predicted the properties of Germanium – Description close to what was later found to be

Ge

He was the first to use table to predict • Work in Progress – Some predictions did not fit –

Te

and

I

fit better in a an inconsistent way – i.e, where the mass number decreased from left - right

Changing the Arrangement

• Mendeleev’s Periodic Table has been improved – Henry Moseley, ~ 1910 – Elements arranged by atomic number • Resolved problems such as at Tellurium – Iodine –

Te

has larger average mass,

I

has 1 more proton – They fit in rows/columns

BETTER THAT WAY

Mendeleev’s Competition

• John Newlands, 1865,

Law of Octaves

Every 8 th element will mimic each other in The Table

• Ordered by Atomic Weights (YET ANOTHER ‘ MASS ’) • Ridiculed and DISS’ED ( dismissed by peers )

Periodic Law

• Metallic properties decrease across

PERIODS

Other properties such as reactivity and conductivity

• • •

GROUPS

have similar properties Groups – Columns Periods - Rows • Elements with similar properties appear at regular intervals –

The Periodic Law

Let’s Describe Some Elements

!!

• The chemical symbol, C, stands for carbon, which has an atomic number of 6 and an atomic mass [

OR, MASS NUMBER

] of 12.01

– Which value is an average ( average of what? ) – Which value also represents molar mass?

Your turn!!

Let’s Describe Some Elements

!!

• The chemical symbol, C, stands for carbon, which has an atomic number of 6 and an atomic mass [

OR, MASS NUMBER

] of 12.01

• KEY QUESTIONS : • How did Mendeleev arrange the elements in his periodic table?

• How are elements arranged in the

MODERN

periodic table?

2 –Exploring the Periodic Table

• KEY QUESTIONS : • Why do elements within a group of the Periodic Table have similar chemical properties?

• What happens to an atom that gains or loses electrons?

• What are the three main categories of elements?

Role of Electrons

• How many electrons in a neutral atom?

• Trends in PT are result of electron arrangement • Valence electrons account for similar properties – Example:

Lithium

and

Sodium

• Element’s location related to electron arrangement

Ion Formation

• What is an “ion”?

• Once an atom gains/loses electrons, it no longer has a balance between protons/electrons – Charges don’t cancel 

atom has net electric charge

• What is easier – GAIN or LOSE electrons?

– Group 1 elements form positive ions ( CATIONS ) – Group 17 elements form negative ions ( ANIONS )

Classifying Elements

• Elements in each category have similar properties •

Metals

Nonmetals

Semiconductors

2 –Exploring the Periodic Table

• KEY QUESTIONS : • Why do elements within a group of the Periodic Table have similar chemical properties?

• What happens to an atom that gains or loses electrons?

• What are the three main categories of elements?

3 –Families of Elements

• KEY QUESTIONS : • What does each element family have in common?

• What are the families of metals?

• What are some non-metal families?

• What are semiconductors

Let’s Classify Elements Further

• Relate

GROUPS

of elements to “family” • Elements in family have same # valence electrons • ONLY

elements

( not compounds ) are in a family

Group Number Group 1 Group 2 Group 3-12 Group 17 Group 18 Number Valence Electrons 1 2 Varies 7 8 ( except He – has 2 ) Name of Family Alkali Metals Alkaline-Earth Metals Transition Metals Halogens Noble Gases

Metals

• • • • INCLUDE: Alkali, Alkaline-Earth, and Transition Alkali metals are very reactive (

Li

and

Na

) Alkaline-Earth metals also fairly reactive – Form compounds found in

human body/limestone

– More

solid

than Group 1 – Means: harder, denser, higher melting temperature Transition metals – less reactive than Group 1-2 – Typically more solid than Group 1-2

Transition Metals

• • Very good catalysts –

Catalyst

: speeds a reaction up / is not reacted H2 and O2 explode in presence of Pt catalyst • • • Some synthetic elements Technetium and Promethium Radioactive (

nuclei decays into smaller atoms

) • Atomic Number > 92 : elements are SYNTHETIC

Nonmetals

• Families include

Noble Gases

and

Halogens

NOBLE GASES: Group 18 ( Ne, Ar, He ) • HALOGENS: Group 17 ( Cl, F, Br ) – Combine easily with metals to form

SALTS

• Nonmetals/compounds plentiful on Earth • Carbon – backbone of life ( organic compounds ) – C forms many other compounds

Semiconductors

• Also called metalloids – B, Si, Ge, As, Sb, Te • Able to

CONDUCT

heat and electricity – BUT only under certain conditions – Silicon (

Si

) is found everywhere!!

– Boron (

B

) used in steel and glass

Hydrogen

Hydrogen

is in a class by itself • 1 proton and 1 electron – Reacts with many other elements • Most abundant element in universe – 3 out of every 4 atoms in universe are

H

3 –Families of Elements

• KEY QUESTIONS : • What does each element family have in common?

• What are the families of metals?

• What are some non-metal families?

• What are semiconductors