Atomic Structure

Atomic Structure

1. Atoms

   • An Atom is the smallest particle of a chemical element that can exist.
     • Atoms consist of electrons which surround the nucleus which consist of protons and newtrons.
       • The sub-atomic particles consist of protons, electrons and newtrons.

2. The Periodic Table

   • There are more than 100 different elements. The periodic table is a chart showing all the elements arranged in a particular way.
     • The Atomic Number is the number of protons in an atom. They are arranged in the periodic table in ascending order of atomic number.
       • Metals tend to have similar properties. They are always good conductors of electricity, and they usually share these properties:
         • high melting point, good conductors of heat, malleable (can be beaten into shape), shiny when cut, ductile (can be pulled into wires)
       • Non-metals have a variety of properties, but very few are good conductors of electricity.
         • Many non-metals have a low melting and boiling point. When non-metals are in a solid state, they are usually brittle so you can’t beat them into shape.
     • The Mass Number of an atom is the total of protons plus neutrons.
   • The Periodic Table has eight main groups. For example, group 1 contains very reactive metals, while group 7 contains very reactive non-metals .
   • The Russian chemist Dmitri Mendeleev published the first widely recognized periodic table in 1869.
     • The vertical columns in the periodic table are called groups. The groups are numbered from left to right. Elements in the same group have similar chemical properties.The number of electrons in the outer shell of all the elements in a group is the same as the group number.

3. Atoms can lose or gain electrons. When they do, they form charged particles called ions

   • if an atom loses one or more electrons, it becomes a positively charged ion
   • if an atom gains one or more electrons, it becomes a negatively charged ion

4. Isotopes are atoms of an element with the normal number of protons and electrons, but different numbers of neutrons. Isotopes have the same atomic number, but different mass numbers.

   • The electronic configuration of an atom is a description of how the electrons are arranged.
     • Valence electrons are the electrons present in the outermost shell of an atom. You can easily determine the number of valence electrons an atom can have by looking at its Group in the periodic table. For example, atoms in Groups 1 and 2 have 1 and 2 valence electrons, respectively.
       • Elements in the same horizontal row are in the same period. The periods are numbered from top to bottom. The period number is the same as the number of occupied electron shells.

5. The History Of The Atom

   • An English scientist called John Newlands put forward his Law of Octaves in 1864. He arranged all the elements known at the time into a table in order of relative atomic mass. When he did this, he found a pattern among the early elements. The pattern showed that each element was similar to the element eight places ahead of it.
   • In 1869, just five years after John Newlands put forward his Law of Octaves, a Russian chemist called Dmitri Mendeleev published a periodic table.
     • Mendeleev also arranged the elements known at the time in order of relative atomic mass, but he did some other things that made his table much more successful. He realised that the physical and chemical properties of elements were related to their atomic mass in a repeating or 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
     • Sometimes this method of arranging elements meant there were gaps in his horizontal rows or 'periods'. But instead of seeing this as a problem, Mendeleev thought it simply meant that the elements which belonged in the gaps had not yet been discovered.

Imagens e arquivos do mapa