what is the present concept of the atom?

Question

do you know....

Answer 1

During the 18th century, Antoine Lavois:er studied the mass relationships between the reactants and products involved in a chemical reaction. As a result of his observations, he suggested that mass was conserved when elements reacted and formed compounds. Additional observations by Joseph Proust (1754-1826), in 1797, indicated that when elements combined and formed compounds, they did so in definite proportions by mass. In 1803, Dalton proposed an atomic theory to explain the mass relationships existing among the substances which take part in chemical reactions. According to Dalton, all substances are composed of small, hard (dense), indivisible particles of matter that resemble tiny billiard balls. He called these particles atoms. Dalton believed that each element consisted of a particular kind of atom, and he attributed the varying properties of the elements to the differences in their atoms. He further proposed that the most important physical difference in the atoms of the various elements was a difference in mass. Accordingly, he assigned separate mass values (atomic masses) to each of the known elements. These were relative masses based on an arbitrarily chosen atomic mass of 1 for hydrogen, the lightest element.

To account for Proust's observations, Dalton proposed that during the formation of chemical compounds, the atoms of elements unite in a definite numerical ratio. Thus, the composition by mass of a given compound is always the same. Dalton further postulated that the total number of atoms of each kind does not change as a result of a reaction. No atoms are gained or lost in a chemical change. This idea explains the conservation of matter noted by Lavoisier.

The group of postulates or assumptions which were advanced by Dalton to explain the nature and behavior of chemical systems is known as Dalton's Atomic Theory.

Some of the points of Dalton's original theory have been modified in accordance with more recent discoveries, but the particle nature of matter and the existence of atoms are now accepted by all scientists. The field-ion microscope, developed in 1955 by Erwin Muller (1899- ) of the Penn~ylvania State University, furnishes the best direct evidence for the atomic nature oi'matter. This instrument, which magnifies by a factor of 4 million, reproduces on a fluorescent screen an image of each atom in a metallic crystal.

Atoms are far too small to be observed directly. The best we can do is to develop a tentative mental picture of the concept. These mental pictures, called models, help scientists to understand and explain abstract concepts. Models serve as useful guides to man's thinking in his search for nature's secrets. Thus, Dalton's billiardball model of atoms helped to clarify the mass relationships that had been observed to exist among the elements in chemical compounds. Although this model is extremely useful both then and now, it is important to avoid taking models too literally. They all have limitations and fall short of reality. The model of atoms has been modified many times since Dalton's time as a result of the work and discoveries of many scientists. Let us briefly examine the evolution of the atomic model from 1800 to the present. We shall investigate several of these concepts in more detail later.
During the 18th century, Antoine Lavois:er studied the mass relationships between the reactants and products involved in a chemical reaction. As a result of his observations, he suggested that mass was conserved when elements reacted and formed compounds. Additional observations by Joseph Proust (1754-1826), in 1797, indicated that when elements combined and formed compounds, they did so in definite proportions by mass. In 1803, Dalton proposed an atomic theory to explain the mass relationships existing among the substances which take part in chemical reactions. According to Dalton, all substances are composed of small, hard (dense), indivisible particles of matter that resemble tiny billiard balls. He called these particles atoms. Dalton believed that each element consisted of a particular kind of atom, and he attributed the varying properties of the elements to the differences in their atoms. He further proposed that the most important physical difference in the atoms of the various elements was a difference in mass. Accordingly, he assigned separate mass values (atomic masses) to each of the known elements. These were relative masses based on an arbitrarily chosen atomic mass of 1 for hydrogen, the lightest element.

To account for Proust's observations, Dalton proposed that during the formation of chemical compounds, the atoms of elements unite in a definite numerical ratio. Thus, the composition by mass of a given compound is always the same. Dalton further postulated that the total number of atoms of each kind does not change as a result of a reaction. No atoms are gained or lost in a chemical change. This idea explains the conservation of matter noted by Lavoisier.

The group of postulates or assumptions which were advanced by Dalton to explain the nature and behavior of chemical systems is known as Dalton's Atomic Theory.

Some of the points of Dalton's original theory have been modified in accordance with more recent discoveries, but the particle nature of matter and the existence of atoms are now accepted by all scientists. The field-ion microscope, developed in 1955 by Erwin Muller (1899- ) of the Penn~ylvania State University, furnishes the best direct evidence for the atomic nature oi'matter. This instrument, which magnifies by a factor of 4 million, reproduces on a fluorescent screen an image of each atom in a metallic crystal.

Atoms are far too small to be observed directly. The best we can do is to develop a tentative mental picture of the concept. These mental pictures, called models, help scientists to understand and explain abstract concepts. Models serve as useful guides to man's thinking in his search for nature's secrets. Thus, Dalton's billiardball model of atoms helped to clarify the mass relationships that had been observed to exist among the elements in chemical compounds. Although this model is extremely useful both then and now, it is important to avoid taking models too literally. They all have limitations and fall short of reality. The model of atoms has been modified many times since Dalton's time as a result of the work and discoveries of many scientists. Let us briefly examine the evolution of the atomic model from 1800 to the present.

Answer 2

In chemistry and physics, an atom (Greek ἄτομος or átomos meaning "indivisible") is the smallest particle of a chemical element that retains its chemical properties. (átomos is usually translated as "indivisible." Until the advent of quantum mechanics, dividing a material object was invariably equated with cutting it.) Whereas the word atom originally denoted a particle that cannot be cut into smaller particles, the atoms of modern parlance are composed of subatomic particles:

electrons, which have a negative charge, a size which is so small as to be currently unmeasurable, and which are the least heavy (i.e., massive) of the three;
protons, which have a positive charge, and are about 1836 times more massive than electrons; and
neutrons, which have no charge, and are about 1838 times more massive than electrons.
Protons and neutrons make up a dense, massive atomic nucleus, and are collectively called nucleons. The electrons form the much larger electron cloud surrounding the nucleus.

Atoms can differ in the number of each of the subatomic particles they contain. Atoms of the same element have the same number of protons (called the atomic number). Within a single element, the number of neutrons may vary, determining the isotope of that element. The number of electrons associated with an atom is most easily changed, due to the lower energy of binding of electrons. The number of protons (and neutrons) in the atomic nucleus may also change, via nuclear fusion, nuclear fission or radioactive decay, in which case the atom is no longer the same element it was.

Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms which have either a deficit or a surplus of electrons are called ions. Electrons that are furthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals.

Atoms are the fundamental building blocks of chemistry, and are conserved in chemical reactions.

Answer 3

The present concept is a very small nucleus (around 10^-15 metres) containing protons and neutrons which is surrounded by a cloud of electrons which is around 10^-10 metres in diameter

Answer 4

with the aid of Experiments. interior the previous an electron beam became shot at a bite of aluminum foil, gold foil, lead foil, copper foil, and others. The pondered, refracted, repelled development of the electron beam became studied and the form of the electron field around the atom became figured. Then a beam of protons became shot on the above foils ... back the pondered, refracted, repelled development of the proton beam have been studied and the form of the internal atom (nucleus) became figured.