Atoms and the periodic table
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Atoms and the periodic table. How did atomic theory develop?. The idea of the atom dates back to 430BC. The atom is defined as the smallest particle that can be considered an element An Englishman, John Dalton, described the atom as an invisible particle that makes up an element.

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Atoms and the periodic table

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Atoms and the periodic table

Atoms and the periodic table

How did atomic theory develop?


Atoms and the periodic table

  • The idea of the atom dates back to 430BC.

  • The atom is defined as the smallest particle that can be considered an element

  • An Englishman, John Dalton, described the atom as an invisible particle that makes up an element.

  • JJ Thomson’s discovery of negatively charged particles called electrons disproved Dalton’s invisible atom idea.


Atoms and the periodic table

  • Rutherford, a former student of Thomson, proposed the existence of nucleus, a small positively charged region of an atom containing positively charged particles called protons.

  • Then a student of Rutherford, Niels Bohr, revised the model to propose that electrons were found only in specific orbits around the nucleus.

  • The modern cloud model proposes that an electron’s movement is related to its energy level and electrons move rapidly within a cloudlike region around the nucleus.


What is the modern model of the atom

What is the modern model of the atom?

  • With the discovery of the neutrally charged neutron, the modern model of the atom emerged.

  • At the center of the atom, is a tiny dense nucleus containing protons and neutrons. Surrounding the nucleus is a cloud like region of moving electrons.

  • Scientists use units known as atomic mass units(amu).

  • Protons have a charge of 1 and a mass of 1 amu.

  • Neutrons have no charge and a mass of 1 amu

  • Electrons have a negative charge and a mass of 1/2000 amu.


Atoms and the periodic table

  • All the mass of an atom is concentrated in the nucleus.

  • Number of protons equals the number of electrons and this is called the atomic number.

  • Definition of an element is based on its atomic number.

  • Atoms of elements that have the same number of protons but a different number of neutrons are called isotopes.

  • An isotope is identified by its mass number which is the sum of the protons and neutrons in the atom


Atoms and the periodic table

  • Summarizing chapter 9,lessons 1-4

  • Mendeleev noticed a pattern of properties in elements arranged by increasing atomic mass

  • The periodic table includes each element’s atomic number, symbol, name and atomic mass.

  • The properties of an element can be predicted from its location in the periodic table.


Atoms and the periodic table

  • Physical properties of metals include luster, malleability, ductility, and conductivity.

  • Metals are classified as alkali metals, alkaline earth metals, transition metals, metals in mixed groups, lanthanides and actinides.

  • Most nonmetals are poor conductors. Solid nonmetals tend to be dull and brittle.

  • The families containing nonmetals include the carbon family, the nitrogen family, the oxygen family, the halogen family, the noble gases, and hydrogen.


Atoms and the periodic table

  • Atomic theory grew as a series of models that developed from experimental evidence

  • At the center of the atom is a tiny dense nucleus containing protons and neutrons. Surrounding the nucleus is a cloudlike region of moving electrons.


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