Atomic Structure

Atomic Structure

1. Experiment

2. Diagrams

   • Electron shells
     • Electrons are arranged in different shells around the nucleus. Each successive shell can only hold a certain number of electrons. The innermost shell is filled first. This shell can contain a maximum of two electrons. The second shell can hold a maximum of eight electrons. When this is filled, electrons go into the third shell, which also holds a maximum of eight electrons. Then the fourth shell begins to fill.
       • A lithium atom, for example, has three electrons. It has two in the first shell and one in the second shell. A carbon atom has six electrons. It has two in the first shell and four in the second shell
         • A calcium atom has 20 electrons. Two are in the first shell, eight in the second shell, eight in the third shell, and two in the fourth shell.

3. Definitions

   • Isotopes
     • any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different atomic weights.
   • Protons
     • a positively charged elementary particle that is a fundamental constituent of all atomic nuclei. It is the lightest and most stable baryon, having a charge equal in magnitude to that of the electron, a spin of ½, and a mass of 1.673 × 10− 27kg. Symbol: P.
   • Electrons
     • An electron is a negatively charged component of an atom . Electrons exist outside of and surrounding the atom nucleus. Each electron carries one unit of negative charge and has a very small mass as compared with that of a neutron or proton .
   • Atomic Mass
     • Atomic mass or atomic weight is the average mass of atoms of an element , calculated using the relative abundance of isotopes in a naturally-occurring element.
   • Radioactive decay
     • Spontaneous disintegration of a radionuclide accompanied by the emission of ionizing radiation in the form of alpha or beta particles or gamma rays.
     • Alpha decay
       • An alpha decay happens because there is an excess of mass. In this type of decay, alpha particles (two protons and two neutrons) are emitted from the nucleus. Both the atomic number and neutron number are reduced by two, so the mass number decreases by four. There are two types of beta decay where the beta particle is either an electron or a positron.
     • Beta decay
       • Beta decay happens because when there are too many neutrons in a nucleus. In this particular case, the element will emit radiation in negative charged particles and they’re called beta particles.
     • Gamma decay
       • Gamma decay is caused when there’s too many energy in the nucleus of an atom. In this case, the particles that have no charge are emitted from the atom. These are called gamma particles.
   • Neutrons
     • an elementary particle having no charge, mass slightly greater than that of a proton, and spin of ½: a constituent of the nuclei of all atoms except those of hydrogen.
   • Atom
     • the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.

4. Problem solving calculations

   • Relative atomic mass
     • The relative atomic mass of an element shows its mass compared with the mass of atoms of other elements. The relative atomic mass of carbon is 12, while the relative atomic mass of magnesium is 24. This means that each magnesium atom is twice the mass of a carbon atom.
   • Relative formula mass
     • Relative atomic masses can be used to find the relative formula mass of a compound.
     • To find the relative formula mass (Mr) of a compound, you add together the relative atomic mass values (Ar values) for all the atoms in its formula.

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