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Atomic Structure


Each atom consists of a very small nucleus composed of protons and neutrons which is encircled by moving electrons. Some of the important properties depend on geometrical atomic structure and also the interaction that exist among the constituent atoms and molecules.

Elements are composed of atoms with characteristics masses. Compounds are composed of small atoms in whole number ratios.

What are Atoms?

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Atoms are tiny units of matter. All matter are made up of matter that occupies space and is made up of atoms. Atoms are the smallest particle of an element that can join up in whole numbers to form molecules.


Atoms sometimes exist by themselves, without connection to other atoms. Mostly though atoms form groups with other atoms. There may be only two atoms in a group or there may be hundreds. These groups of atoms are called molecules.

Atomic Structure Definition

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"Atom is the tiniest particle which cannot be further divided." The concept of indivisibility of atom is given by John Dalton.

The modern view about the structure of atom suggests.
  1. Inside the nucleus, protons and neutrons are present which are collectively called nucleons.
  2. The electrons are revolving around the nucleus in fixed orbits.
  3. The mass of an atom is concentrated inside the nucleus of an atom.
  4. Atom is electrically neutral.

Model of the Atom

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One early outgrowth of quantum mechanics was the simplified Bohr atomic model, in which electrons are assumed to revolve around the atomic nucleus in discrete orbitals and the position of any particular electron is more or less well defined in terms of its orbital.

Model of the Atom

The energies of electrons are quantized. The electrons are permitted to have only specific values of energy. An electron may change energy but in doing so it must make a quantum jump either to an allowed higher energy or to a lower energy. Bohr model is an early attempt to describe electrons in atoms both in terms of position and energy.
The basic building block of any substance is the atom. Every element and compound is made up of one or more atoms. In making up of the atom an atom is made up of only one nucleus but can have several shells. Within the nucleus protons and neutrons are present. Every element has a specific number of protons. For example, carbon will always have six protons and oxygen will always have eight protons. The number of protons corresponds to the atomic number of the element.

Electrons orbit around the nucleus much way planets orbit the sun. These electrons are said to reside in shells sometimes called orbits or rings. Protons and electrons are electrically charged. Protons are positively charged and electrons are negatively charged. Neutrons have no electrical charge and thus they have very little bearing on an atoms electrical activity.

The structure of the atom and the electrical charges associated with parts of the atom are shown below.

Structure of an Atom

Summary of atomic structure is give below.

Parts of the atom
1 Proton Nucleus
+1 1
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Atomic Structure Timeline

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In the early 20th century science and technology continued to develop. Max Plancks quantum theory (1900), Albert Einstein special theory of relativity (105), and Neils Bohr's theory of atomic structure (1913 - 15) were among the most notable scientific advancement.

The diagrammatic representation of atomic structure timeline and the scientist worked on atomic theory is shown below.

Atomic Structure Timeline

Atomic Structure Chart

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The atoms were believed to be the minute, indivisible particles of which all material things were made. The nucleus was thought to consist of protons and neutrons and to form an atom, only electrons needed to be added in external shells. Therefore protons, neutrons and electrons were considered as the elementary particles.

Atomic structure of some of the atoms are listed below.

Atomic structure
Atomic structure of hydrogen Atomic Structure of Hydrogen
Atomic Structure of Carbon
Atomic Structure of Carbon
Atomic structure of oxygen
Atomic Structure of Oxygen
Atomic structure of gold
Atomic Structure of Gold
Atomic structure of sodium Atomic Structure of Sodium
Atomic structure of nitrogen
Atomic Structure of Nitrogen
Atomic structure of helium
Atomic Structure of Heliwm
Atomic structure of copper Atomic Structure of Copper
Atomic structure of neon
Atomic Structure of Neon
Atomic structure of iron
Atomic Structure of Iron
11 Atomic structure of magnesium Atomic Structure of Magnesium
Atomic structure of aluminum
Atomic Structure of Aluminum
Atomic structure of lithium
Atomic Structure of Lithium
14 Atomic structure of chlorine Atomic Structure of Chlorine
Atomic structure of sulfur
Atomic Structure of Sulfur

History of Atomic Structure

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By the second half of the 1800s many scientist believed that all the major discoveries related to the elements had been made.
  1. J.J.Thomson discovered the electron beam in a cathode ray tube in 1897.
  2. During the late nineteenth and early twentieth centuries, more and more physicists turned their attention to the structure of the atom.
  3. In 1913 Danish scientist Neils Bohr published a theory explaining the line spectrum of atomic theory.
  4. The work of Louis de Broglia and others in the 1920s and 1930s showed that quantum theory had a more probabilistic model of where the electrons could be found that resulted in the theory of orbitals.
  5. Even today the search goes on to study the particle of the atom and to attempt to control nuclear reactions as a source of energy.
Group I elements in the periodic table are called alkali metals. The hydroxides of these metals are very strong alkalies. The alkali metals includes Li, Na, K, Rb, Cs and Fr. Alkali word comes from Arabic word means plant ashes. These elements lies in s-block elements. These metals are soft, shiny and highly reactive.
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Alkaline earth metal oxides were known much earlier than the metals themselves. These metals are alkaline in nature like alkali metal oxides. Those metals are found in earths crust. They are placed in group II in the periodic table and includes Be, Ca, Mg, Sr, Ba and Rn. Among these metals Ca and Mg are the most abundant metals.
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The elements boron (B), Al, Ga, In, Tl constitute group 13 of the periodic table. Except boron which is classified as a non metal all other elements of this group are metals. All the elements of this group have three electrons in their valence shell.
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The elements of carbon family are carbon, silicon, Germanium, Tin and Lead. All these elements except lead exhibit allot ropy. All the carbon family elements form monoxides however SiO and GeO are highly unstable.
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Nitrogen family consists of elements nitrogen, phosphorus, arsenic, antimony and bismuth. Nitrogen family elements also show tendency of catenation but to lesser extent compared to carbon family.
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Oxygen family elements presented belong to group 16 of the long form of periodic table. Except Po all other elements are also called chalogens, which means ore or mineral forming elements.
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Fluorine, chlorine, bromine, iodine, astatine elements belong to halogen family. All the halogens show a common oxidation state of -1. Halogen and inter halogen compounds with halide ions form poly halide indirectly.
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Metals are elements that conduct heat and electricity. Elements can be classified as metals, non-metals and metalloids. In a periodic table, metals are arranged on the left side and non-metal on the right side, while metalloids are present as a connecting line between metals and non metals.
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The electronegativity of a bonded atom is defined as its relative tendency (or ability) to attract the shared electron pair towards itself. on moving right to left in the periodic table electronegativity increases and down the group it decreases.
→ Read More Molecular dynamics revolutionized the field of realistic computer simulation of complex molecular systems and processes, including chemical reactions , by unifying molecular dynamics and electronic structure theory.
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3 Subatomic Particles

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The three subatomic particles are given below.
  1. Electron - Negatively charged particle present outside the nucleus of an atom.
  2. Proton - Protons are positively charged and are present inside the nucleus.
  3. Neutron - Neutrons are neutrally charged particles, present within the nucleus of an atom.
In an atom, electrons filled in different levels according to their energies. First electrons filled in low energy levels and then move to higher energy level. The outermost energy level in an atom is called as valence shell and electrons placed in this shell are known as valence electrons.
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The chemical bond between two atoms in which the electrons (in pairs) are shared by both the participating atoms is called as a covalent bond is known as octet rule.
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