Atomic structure

Atomic structure

1. The mass of an atom is concentrated in its minute, positively charged nucleus

2. Atoms contain a positively charged dense nucleus composed of protons and neutrons (nucleons)

3. Electrons, Protons + Neutrons

   • Negatively charged electrons occupy the space outside the nucleus
   • Nucleus and energy levels
     • Protons - found in nucleus, Neutrons - found in nucleus, Electrons - surround the nucleus in energy levels
   • Electrons do not follow in specific paths around the nucleus. They move very quickly and pop in and out of existence!
   • Amount of protons identifies the element
     • If you have an ion, your electrons will be either more or less than the protons depending upon the charge.
     • To be neutral, the electrons and protons MUST be equal
   • The difference in neutrons does affect physical properties like boiling and melting points, mass, density and rate of diffusion for gases. Physical property is something that can be measured without chaniging the chemical composition of the substance.
   • Isotopes show that when they have more neutrons they are heavier and therefore move slowly at a given temperature.

4. Element

   • Substance that cannot be broken down into simpler substances by a chemical reactions

5. Atom

   • Smallest particle (species) of an element that retain the properties of that element
   • Atomic number = Number of protons in the nucleus, Mass number = Number of protons PLUS neutrons in the nucleus, Isotope = Atoms of the same element and have same number of protons but different number of neutrons
     • Mass number = Protons + neutrons, Atomic number = Protons
   • Ion
     • Negative ion formed by the gain of one or more electrons
   • Cation
     • Positive ion formed by the loss of one or more electrons
   • Anion
     • Negative ion formed by the gain of one or more electrons

6. Compound

   • The chemical combination of two or more elements

7. Models of the atom

   • Dalton's atomic theory
   • Thomson's plum pudding model = Discovered the electron
   • Rutherford's gold foil experiment = Discovered the proton
   • Bohr's Solar system model = Found that electrons orbit the nucleus
   • Quantum Mechanical Model = Modern theory where electrons exist in cloud shapes or "orbitals"

8. Energy levels

   • N = 1,2,3,4,5,...etc
   • They are NOT evenly spaced, the higher energy level you have, the closer they will be to each other.
   • Sublevels
     • AKA "atomic orbitals"
       • Orbitals are referred to as S, P, D, F. The shapes of atomic orbitals depend on the energy levels.

9. Mass spectrometer

   • Measures the masses of different isotopes and their relative abundance.
     • Ionisation, Acceleration, Deflection and Detection
     • Relative atomic mass = Average mass of an element taking into account all its isotopes and their relative abundance. This is why the atomic mass is not a whole number
       • Calculation of relative atomic mass of an element that has two isotopes = Multiply the isotope mass by the abundance and add them together.
     • Calculation of relative abundance of two isotopes using periodic table
       • Multiply the isotope mass by the abundance to get total mass (let the smallest be x and the largest number be 1-x)