CHAPTER 1 Flashcards
What is the difference between the concepts of ‘basic substance’ and ‘simple substance’? Illustrate this with an example.
The definition of “element” given by Mendeleev and that of “basic substance” given by Paneth are similar in that they both refer to fundamental building blocks of matter. However, there are some differences between the two concepts.
According to the information in the PDF, Mendeleev defined an element as a material particle of simple and compound substances that determines their behavior from a chemical and physical point of view. He associated the concept of an element with the idea of an atom, and considered it to be an abstract, but strictly associated with empirical experience. In contrast, Paneth used the term “basic substance” to refer to what is indestructible in compounds, and which survives in compounds. He identified basic substances by their atomic number, and considered them to be completely unobservable to our senses, and just bearers of properties, while at the same time devoid of any property.
Therefore, while both concepts refer to fundamental building blocks of matter, Mendeleev’s definition of an element is more closely associated with the idea of an atom, and emphasizes the role of elements in determining the behavior of substances, while Paneth’s concept of a basic substance is more focused on the indestructible component of compounds.
Give a summary of Aristotle’s four elements theory.
Aristotle’s four elements theory was based on the idea that all matter was made up of four basic elements: fire, air, earth, and water. Aristotle discarded Plato’s mathematical approach, but kept Empedocles’ theory of four elements.
Aristotle believed that these elements were not fundamental matter, but rather simple perceptible bodies that underlie perceptible bodies. He also believed in the existence of a “primary material” which is a substrate for “qualities” (hot, cold, dry, and wet), but is inseparable from those qualities. Each element was provided with a pair of qualities.
Aristotle’s theory of the four elements was influential in the development of later theories of matter, such as the medieval theory of the four humors, which associated the four elements with bodily fluids and personality traits. However, the theory was eventually replaced by more sophisticated models of atomic structure, which showed that matter was made up of atoms and subatomic particles, rather than the four basic elements. 5
How does the meaning of the concept ‘element’ used by the Greek philosophers differ from our current definition of this concept?
he meaning of the concept “element” used by the Greek philosophers differs from our current definition of this concept.
In antiquity, the term “element” comprised two different notions. From Thales to Empedocles, the concept of an abstract conserved entity was used. Aristotle, on the other hand, used the term to refer to the direct carrier of properties, such as water as the carrier of the cold and the wet.
In contrast, our current definition of the concept “element” is based on the modern theory of atomic structure, which defines an element as a substance that cannot be broken down into simpler substances by chemical means. Each element is characterized by a unique number of protons in the nucleus of its atoms, which determines its atomic number and its position in the periodic table.
Therefore, the Greek concept of “element” was more abstract and focused on the properties of matter, while our current definition is more concrete and based on the structure of matter at the atomic level. 11
Compare the definition of ‘element’ given by Mendeleev with that of ‘basic substance’ given by Paneth.
Mendeleev’s definition of “element” and Paneth’s definition of “basic substance” are related but distinct concepts.
Mendeleev defined an element as a material particle of simple and compound substances that determines their behavior from a chemical and physical point of view. He considered an element to be an abstract, but strictly associated with empirical experience, material part of a compound that corresponds to the idea of an atom.
In contrast, Paneth defined a basic substance as what is indestructible in compounds and survives in compounds. It is completely unobservable to our senses and is just a bearer of properties, while at the same time devoid of any property. A basic substance is identified by the atomic number Z.
Therefore, while both concepts refer to the fundamental building blocks of matter, Mendeleev’s definition of an element is more closely related to the idea of an atom and its role in determining the behavior of compounds, while Paneth’s definition of a basic substance is more focused on the indestructible component of compounds that carries their properties. 31 29
Why did Lavoisier consider ‘heat’, ‘light’, barite (= BaSO4), and alu- mina (= Al2O3) as chemical elements, although we no longer consider them as elements?
Lavoisier considered “heat” and “light” as elements because he believed that they were fundamental substances that could not be further decomposed. However, these substances were later found to be forms of energy rather than chemical elements.
Lavoisier also considered barite and alumina as elements because they were simple substances that could be isolated and could not be further decomposed by chemical means. However, these substances were later found to be compounds of other elements, specifically barium, sulfur, aluminum, and oxygen.
Therefore, Lavoisier considered these substances as elements based on the knowledge and techniques available at the time, but as scientific understanding advanced, it became clear that they were not fundamental building blocks of matter. Instead, they were either forms of energy or compounds of other elements. 19
Describe Mendeleev’s definition of chemical element.
Mendeleev’s definition of a chemical element is based on the idea that an element is a material particle of simple and compound substances that determines their behavior from a chemical and physical point of view.
Mendeleev distinguished between the terms “simple substance” and “element.” A simple substance is somewhat material, endowed with physical properties and capable of chemical reactions. It is able to display itself in the form of allotropic modifications and is distinguished from a compound substance only by the homogeneity of its material parts.
In contrast, an element is an abstract, but strictly associated with empirical experience, material part of a compound that corresponds to the idea of an atom. It is those material particles of simple and compound substances which determine their behavior from a chemical and physical point of view. An element is invisible, but strictly associated with the empirical experience, and corresponds to the idea of an atom.
Therefore, Mendeleev’s definition of a chemical element emphasizes the role of elements as fundamental building blocks of matter that determine the behavior of simple and compound substances from a chemical and physical point of view. 29
What are Lavoisier’s restricted and extended laws of conservation of elements? Compare those 2 laws.
Lavoisier’s restricted law of conservation of elements states that elements that enter into a compound can be recovered from it, both qualitatively and quantitatively. For example, hydrogen and oxygen gas can combine to form water, but water can be split to form hydrogen and oxygen gas again.
Lavoisier’s extended law of conservation of elements goes further and states that the elements that enter into a compound are not only recoverable from it, but they are also actually present in the compound. Lavoisier arrived at this conclusion from the empirical fact that water could be both synthesized from hydrogen gas and oxygen gas (2H2 + O2 → 2H2O), as well as being decomposed into hydrogen and oxygen gas (2H2O → 2H2 + O2). He concluded that both gases were actually present in the water, i.e. 2H2O = 2H2 + O2.
The restricted law of conservation of elements is a more basic principle that simply states that the elements that enter into a compound can be recovered from it. The extended law of conservation of elements builds on this principle and goes further to state that the elements are actually present in the compound.
Therefore, while both laws emphasize the recoverability of elements from compounds, the extended law goes further to assert the actual presence of the elements in the compound. 23
Dalton defined the chemical atom as the smallest quantity of a sub- stance still showing the properties of the whole. Explain how Dalton’s atomic model led to a contradiction.
Dalton’s atomic model led to a contradiction because it assumed that atoms were both indestructible and unchangeable, and that each element was made up of one unique type of atom with a characteristic atomic mass. However, this assumption did not explain why compounds made up of different elements did not exhibit the characteristic properties of those elements.
For example, if an iron sulfide molecule consisted of a minute piece of sulfur joined to a minute piece of iron, how then is it possible that the elements iron and sulfur are deprived of almost all their characteristic properties, in spite of their being present in the compound? Similarly, why is iron sulfide, though containing so much sulfur, not dissolved by carbon disulfide (a good solvent for sulfur)? And why is iron sulfide not strongly ferromagnetic, though it contains so much iron?
These contradictions in Dalton’s atomic model were not resolved until later developments in atomic theory, which showed that atoms were not indestructible and unchangeable, but could be broken down into smaller particles, such as protons, neutrons, and electrons. This led to the development of more sophisticated models of atomic structure, such as the Bohr model and the quantum mechanical model, which better explained the behavior of atoms and their interactions with other atoms to form compounds. 28 27
What are the postulates of Dalton’s atomic theory?
he postulates of Dalton’s atomic theory are as follows:
- Elements are made of tiny particles called atoms.
- The atoms of a given element are different from those of any other element, and the atoms of different elements can be distinguished from one another by their respective relative atomic mass.
- All atoms of a given element are identical.
- Atoms of one element can combine with atoms of other elements to form chemical compounds, and a given compound always has the same relative numbers of types of atoms.
- Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process, and a chemical reaction simply changes the way atoms are grouped together.
These postulates formed the foundation of modern atomic theory and were proposed by John Dalton in his book “New System of Chemical Philosophy” in 1808. They helped to explain the behavior of matter in terms of the behavior of atoms, and they provided a framework for understanding the composition and properties of chemical compounds.
Therefore, the postulates of Dalton’s atomic theory include the ideas that elements are made of atoms, atoms of different elements are different, all atoms of a given element are identical, atoms can combine to form compounds, and atoms cannot be created, divided, or destroyed in chemical reactions. 26
Where did the alchemical idea of transmuting base metals (e.g. lead) into gold originate from?
the alchemical idea of transmuting base metals (e.g. lead) into gold originated from Aristotle’s idea that an element might be transformed into another element by a change of its qualities. The alchemists of the Middle Ages and the Renaissance were interested in this idea and sought to apply it to the transmutation of metals. They believed that base metals could be transformed into noble metals like gold and silver by a process of purification and transformation.
The alchemists developed their own postulates about the unity of matter and the transmutation of metals, and they used the term “principle” rather than “element” to describe the basic building blocks of matter. They believed that there was a transmuting agent called the Philosopher’s Stone that could turn base metals into gold, and that this stone was also man’s perfect medicine and the elixir of life.
Therefore, the alchemical idea of transmuting base metals into gold originated from Aristotle’s idea that an element might be transformed into another element by a change of its qualities, and it was developed further by the alchemists of the Middle Ages and the Renaissance. 12
What is the difference between an element and an isotope?
an element is a pure chemical substance composed of atoms with the same number of protons in the atomic nucleus. In other words, all atoms of a given element have the same atomic number, which is equal to the number of protons in the nucleus. For example, all carbon atoms have 6 protons in the nucleus, so carbon is an element with atomic number 6.
On the other hand, an isotope is a variant of an element that has the same number of protons in the atomic nucleus, but a different number of neutrons. This means that isotopes of the same element have the same atomic number (number of protons) but different mass numbers (number of protons + number of neutrons). For example, carbon-12 and carbon-14 are both isotopes of carbon, since they both have 6 protons in the nucleus, but carbon-12 has 6 neutrons while carbon-14 has 8 neutrons.
Therefore, the main difference between an element and an isotope is that an element is defined by the number of protons in the atomic nucleus, while an isotope is defined by the number of neutrons in addition to the number of protons. 35
Why did Mendeleev select the atomic weight as the fundamental prop- erties of a basic substance?
Mendeleev selected the atomic weight as the fundamental property of a basic substance because he believed that the atomic weight was a more fundamental property than other properties like density or melting point. He recognized that the atomic weight of an element was related to its chemical properties, and that elements with similar atomic weights tended to have similar chemical properties.
Mendeleev also recognized that the atomic weight of an element was a measurable quantity that could be determined experimentally, and that it was relatively easy to obtain accurate atomic weight measurements for many elements. He used these atomic weight measurements to construct his periodic table, arranging the elements in order of increasing atomic weight and grouping together elements with similar chemical properties.
Therefore, Mendeleev selected the atomic weight as the fundamental property of a basic substance because he believed it was a more fundamental property than other properties, it was related to the chemical properties of elements, and it was a measurable quantity that could be used to construct a periodic table. 30
Elaborate the statement: “For Mendeleev, the periodic table is a classification of elements, not of simple substances as conceived by Lavoisier.”
Mendeleev’s definition of an element differed from Lavoisier’s definition in that Mendeleev considered an element to be a material particle of a simple or compound substance that determined its behavior from a chemical and physical point of view. In other words, Mendeleev believed that an element was an abstract concept that was associated with the empirical experience of observing the behavior of substances, rather than a material substance in and of itself.
Based on this definition of an element, Mendeleev constructed his periodic table as a classification of elements, rather than a classification of simple substances as conceived by Lavoisier. Mendeleev arranged the elements in order of increasing atomic weight, and grouped together elements with similar chemical properties. He believed that the periodic table was a way of organizing the elements based on their fundamental properties, and that it could be used to predict the properties of undiscovered elements.
In contrast, Lavoisier considered a simple substance and an element to be synonyms, and believed that all substances were composed of combinations of elements. He did not recognize the existence of different forms of the same element, such as allotropic forms of carbon like graphite and diamond.
Therefore, the statement “For Mendeleev, the periodic table is a classification of elements, not of simple substances as conceived by Lavoisier” means that Mendeleev’s periodic table was based on a different definition of an element than Lavoisier’s, and that it was constructed as a way of organizing the elements based on their fundamental properties rather than as a way of classifying simple substances. 29
Compare Boyle’s and Lavoisier’s definitions of a chemical element.
Boyle and Lavoisier both proposed definitions of a chemical element, but their definitions differed in several ways.
Boyle defined an element as a body which is not subject to analysis, and he theorized about the microstructure of matter. However, he did not dare to name any substances as elements, and he did not see any satisfactory method to determine which substances are true elements. Therefore, Boyle’s definition of an element was more theoretical and less empirical than Lavoisier’s definition.
In contrast, Lavoisier defined an element as a simple substance that can be isolated and cannot be further decomposed. He identified the elements on an experimental basis, using state-of-the-art analytical methods to decompose compound substances into simple substances. Lavoisier’s definition of an element was based on empirical observations and experiments, and he used it to compose a list of simple substances or elements.
Therefore, the main difference between Boyle’s and Lavoisier’s definitions of a chemical element is that Boyle’s definition was more theoretical and less empirical, while Lavoisier’s definition was based on empirical observations and experiments. Boyle theorized about the microstructure of matter and did not see a satisfactory method to determine which substances are true elements, while Lavoisier used state-of-the-art analytical methods to decompose compound substances into simple substances and composed a list of elements based on empirical observations. 19
Why is it wrong to state that the density of carbon is 2.267 gcm−3 ?
it is wrong to state that the density of carbon is 2.267 gcm−3 because different allotropic forms of carbon have different densities. The density of an allotropic form of carbon must be specified in order to accurately describe the density of carbon.
For example, the allotropic form of carbon known as graphite has a density of 2.267 gcm−3, which is the density that is often cited for carbon. However, other allotropic forms of carbon, such as diamond, have much higher densities. Therefore, it is important to specify which allotropic form of carbon is being referred to when discussing the density of carbon.
In summary, it is wrong to state that the density of carbon is 2.267 gcm−3 because different allotropic forms of carbon have different densities, and the density of an allotropic form of carbon must be specified in order to accurately describe the density of carbon. 34
