Francisco Javier Cervigon Ruckauer, Metales y metaloides o semimetales, Metals and metalloids

Badge Insignia del curso Metal and Metalloids of the Main Groups: Basis and Their Role in the Daily Life

Badge Insignia del curso

Metales y Metaloides de los Grupos Principales: Bases y Su Papel en la Vida Diaria /

Metal and Metalloids of the Main Groups:

Basis and Their Role in the Daily Life

Francisco Javier Cervigon Ruckauer

Archivo del curso, Course file Metal and Metalloids of the Main Groups: Basis and Their Role in the Daily Life

Archivo del curso, Course file

Metal and Metalloids of the Main Groups:

Basis and Their Role in the Daily Life

Francisco Javier Cervigon Ruckauer

Course index Francisco Javier Cervigon Ruckauer

Course index

0. Introduction to the course
Course introduction
Laboratory experiments
Discussion forums
Useful information

1. Acid & base and redox properties of elements
Basic acid & base concepts
Basic Redox Concepts
Design and interpretation of redox and pH diagrams
Interview with students

2. Group I
Properties and trends of alkali metals
Isolation and applications of alkali metals
Basic chemicals of alkali metals
Interview with students

3. Group II
Properties and trends of alkaline-earth metals
Isolation and applications of alkaline-earth metals
Basic chemicals of alkaline-earth metals
Interview with students

4. Elements of group 13
Properties and trends of elements of group 13
Boron
Aluminium
Gallium, indium and thallium
Interview with students

5. Elements of group 14
Properties and trends
Silicon
Germanium, tin and lead
Interview with students

6. Metals and metalloids of group 15 & 16
Properties and trends of metals and metalloids of group 15 & 16
Arsenic, antimony and bismuth
Tellurium and polonium
Interview with students

Farewell
Interview with students
Acknowledgements
Badge , current section
Certificate
Exit survey
Francisco Javier Cervigon Ruckauer

0. Introduction to the course. Course introduction Francisco Javier Cervigon Ruckauer

0. Introduction to the course.

Course introduction

COURSE OVERVIEW

This course deals with the study of metals and metalloids from what are known as “Main Groups” of the Periodic Table. During this course the student will have the opportunity to discover how an element occurs in nature, how it can be obtained and for which important applications it is used. Additionally the study of physical and chemical properties of these elements will help learners to understand and consolidate all the basic concepts acquired in a General Chemistry course, such as the study of chemical reactions, and the thermodynamics, kinetics and equilibrium of those reactions. After the course, the student will be able to analyse the suitability of a determined element for some application. This relationship with real life will contribute to the engagement of the student during the course.

During the first week of the course we will review the main acid/base theories and oxidation/reduction concepts, which will be a key factor for assimilating most of the content of this course. The student will learn how to construct and interpret redox diagrams, such as Latimer and Frost diagrams, which are really useful for visualising the most stable oxidation states of the elements. Moreover, during this first week, we will also show the construction and interpretation of Ellingham diagrams, which are really important in order to rationalise the process of extraction of a metal from its ore.

From the second week until the end of the course we will go over what it are known as “The Main Groups” of the Periodic Table, by exploring and studying metal and metalloid elements present in those groups. There will be a descriptive study of each element where we will review all their physical and chemical properties. We will pay more attention to the elements and combinations that are most useful in our lives, so we will end up every week with a series of compounds for each studied group, which are relevant in our society.

The course has been structured in videos, where basic ideas are presented, and some text readings recommended, in order to gain a deeper insight into specific physical and chemical data, such as density values, ionisation energy data, main reactivity, abundance of the elements on earth and so on. We have also included an experiment recorded in our laboratory facilities which will be really useful for seeing chemistry in action and conveniently understanding all concepts learned during the week.

The course’s assessment will be based on some small problems between the videos, homework given at the end of the week and a final exam the last week of the course. For a detailed explanation about how will be the assessment developed please consult the grading policy of the course. We have estimated around 4-5 hours per week in order to complete successfully all the content.

PRERREQUISITES

To complete the course satisfactorily, basic knowledge in general chemistry is recommended, especially in acid-base and redox concepts. However, the course has been designed to also be accessible to less-qualified students, incorporating supporting material to better understand the key concepts.

GOALS OF THE COURSE

By taking this course, students will achieve the following objectives:

Master and apply fundamental concepts of general chemistry, such as acid/base and redox equilibria, kinetics, and thermodynamics.
Interpret and construct Latimer and Frost diagrams what will be really useful for predicting the relativity stability of the different oxidation states of an element.
Be able to interpret the extraction of metals from their corresponding ores by employing an Ellingham Diagram.
Rationalise the properties of an element according its position in the Periodic Table and be able to predict its chemical behaviour.
Understand the occurrence and the obtaining process of the studied elements and their most industrially demanded combinations.
Recognise the importance and relevance of metals and metalloids in our daily life.
Apply theoretical principles to real situations by visualising different laboratory experimental processes.

Francisco Javier Cervigon Ruckauer

1. Acid & base and redox properties of elements. Basic acid & base concepts Francisco Javier Cervigon Ruckauer

1. Acid & base and redox properties of elements

Basic acid & base concepts

ARRHENIUS, BRØNSTED-LOWRY AND LEWIS THEORIES

Saltar a una versión navegable de la transcripción de este curso.

FACTORS INFLUENCING ACID-BASE STRENGTH

Saltar a una versión navegable de la transcripción de este curso.

ACID-BASE TRENDS IN THE PERIODIC TABLE

Carefully analysing all trends and behaviors described in the previous sections we can easily observe clear trends in acidity and basicity based upon where the elements lie in the Periodic Table.

It is clear that when we move along a row from left to right in the Periodic Table there is a transition from basic to acid properties. Let’s examine what happens in period 3 which is in agreement with this behavior.

Sodium, the first element of the row, is present as sodium ion,

Na+, for all pH intervals while calcium, the next element in the row, is forming calcium hydroxide at higher pH values. Aluminium exhibits amphoteric properties, due to the fact is present in solution as

Al3+ for low pH values and as the aluminate ion

[Al(OH)4]−,at higher pH values. When we move at intermediates pH, aluminium is in the form of the insoluble hydroxide,

Al(OH)3 . In the case of silicon, cationic solutions are not formed even at low pH values, instead forming hydrated

SiO2 . When we move at strongly alkaline pH it dissolves to form different ions such as

[SiO(OH)3]− ; and

[SiO2(OH)2]− .The next elements of the row, phosphorus, Sulphur and chlorine are all non-metals and none of them are found in solution as a free cation. Their oxides react with water to form the corresponding oxoacid. If we compare oxoacids of much higher oxidation state, e.g. phosphoric acid, sulphuric acid and perchloric acid, the strength of this oxoacids increases along the row as was discussed in the previous section.

We can take a similar approach about how the acid and base properties vary along a column or group in the Periodic Table. The general behaviour is that descending the column elements turn more basic. We see this pattern if we examine the

pka values of the oxoacids with the highest oxidation state of elements of group 15. While nitric acid is a strong acid, phosphoric and arsenic acids are weak with similar values of

pka, antimonic acid is amphoteric whilst the corresponding bismuth compound,

Bi(OH)3 is weakly basic.

Another important correlation can be established between the oxidation state and the acid or base properties. The higher the oxidation state the higher their acidic properties. This effect is highly notorious for elements of the transition series not covered in this course.

ACID-BASE PROPERTIES OF OXIDES

The oxides of the elements can be classified as: acidic, basic, amphoteric or neutral.

Acidic oxides are those oxides which dissolve in water to give an acidic solution (e.g.

P2O5,

N2O5,

Cl2O7 , etc.) or an oxide insoluble in water but which dissolve in excess alkali (e.g.

SiO2 ).

Basic Oxides are those which dissolved in water give basic solutions (e.g.

Na2O,

CaO, etc.) or insoluble in water and which dissolve in excess acid (e.g.

MgO)

Amphoteric oxides are usually insoluble in water but dissolve in both alkali and acids. (e.g.

Al2O3,

BeO,

Bi2O3)

Neutral Oxides which do not interact with any other oxide, dissolve in water to give neutral solution or are insoluble at any pH (e.g

CO,

NO)

Basic oxides are the anhydrides of strong bases as illustrated by the following equilibria:

N a 2 O (s) + H 2 O (l) \to 2 N a O H (s)

These basic oxides are combinations of oxygen with electropositive metals of group 1 and 2. They are ionic compounds while covalent oxides are the combinations of oxygen with most of the nonmetallic elements of the Periodic Table. These covalent oxides are acidic and they are the anhydride of the corresponding acid, as the following equations show

P 4 O 10 (s) + 6 H 2 O (l) \to 4 H 3 P O 4 (a q)

S O 3 (g) + H 2 O (l) \to H 2 S O 4 (a q)

One of the most typical reactions of the oxides is the reaction of an acid and a base oxide to form a salt. For example the following reactions to produce two important compounds involve this type of reaction:

C a O (s) + S O 2 (g) \to C a S O 3 (s)

C O 2 (g) + 2 N a O H (a q) \to N a 2 C O 3 (a q) + H 2 O (a q)

In the case of an amphoteric oxide such as

Al2O3 or

ZnO, they will react with both acids and base, as the for example:

A l 2 O 3 (s) + 6 H C l (l) \to 2 A l C l 3 (a c) + (a c)

A l 2 O 3 (s) + 2 N a O H \to 2 N a A l O 2 (a c) + H 2 O (a c)

It is remarkable to note that if we compare the oxides of the elements of the second row, there is a transition from the more basic oxides on the left to the more basic oxides to the right. The acidic character of non-metallic oxides increase with the increase in oxidation number of the elements. It is also interesting to consider a similar trend along a column, as can be illustrated in group 14.

CO2 is a weak acid but down the group the oxide becomes increasingly ionic and less acid and

PbO2 is amphoteric.

THE HARD AND SOFT ACIDS AND BASES: THE HSAB CONCEPT

It seems reasonable and useful to establish an unambiguous way to order the basic and acid character of Lewis acids and bases in a similar way as we did with BrØnsted-Lowry species in the previous section. According to the Lewis theory of acid and bases, they react as shown in the following equation to form the corresponding complex

A + : B \to A : B

Thus, we can establish a similar scale to that presented in the previous section if we can rationalise the interaction between Lewis acids and bases.

The more favorable this interaction the more stable the complex will be. However, it turns out to be an extremely difficult and challenging task because the coordination between Lewis acids and bases can vary widely. For example,

BCI3shows greater acidity than

BF3 with respect to bases such as

NH3while toward weaker bases such

CO,

BF3 is a stronger acid than

BCI3. In order to deal with this situation a number of qualitative relationships were developed to categorise Lewis acids and bases. In 1963 American chemist R. G. Pearson suggested a systematic form to approach this situation based on the concepts of hardness and softness. According to the descriptions given by Pearson, hard acids are those having high positive charge, small size and the absence of outer electrons. They have a low polarizability (the ability to distort the electron cloud of a specie), while the soft acids have the opposite characteristics. A hard base usually has high electronegativity, low polarizability, and are difficult to oxidize while soft bases have the opposite characteristics. According this classification Pearson establishes that the most favorable interactions occur when the acid and the base have similar electronic character. This is the HSAB principle, and can be summarised as hard acids preferring hard bases and soft acids preferring soft bases.

A number of Lewis acids and bases have been assigned to hard or soft groups according what we have explained above (see table 1), although it is hard to determine the exact line of separation of both categories and therefore some species are considered as intermediate or borderline cases

Francisco Javier Cervigon Ruckauer