ATOM & STOICHIOMETRY

Nota:

• Occupies space & mass exist everywhere exc. vaccum solid, liquid & gas

1. pure subtances
   1. element

      Nota:

      •  is a substance that cannot be separated into simpler substances by chemical means 
   2. compound

      Nota:

      • a substance composed of atoms of two or more elements chemically united in fixed proportions
2. mixtures
   1. homogenous
   2. heterogenous

      Nota:

      • wet sand

Nota:

•  The smallest unit of an element. Consists of a nucleus and electrons.   Atom cannot be created, destroyed or split.

1. molecules

   Nota:

   •  Two or more atoms combine together(held together by a strong chemical bond) i.e. H2, O2, N2
2. ions

   Nota:

   • charged atom
   1. cation (+)

      Nota:

      •  an atom that has lost one or more electrons making it positively charged.
   2. anion (-)

      Nota:

      • an atom that gained one or more electrons making it negatively charged 
   3. polyatomic ion

      Nota:

      •  ions that contain two or more atoms in it.  e.g: OH- , NO3-, CO32-, NH4+ 

Nota:

•  Also known as subatomic particles   A typical atom consists of a nucleus composed of positively charged protons and neutral neutrons surrounded by a cloud of orbiting negatively charged electrons   Proton and neutrons join together to form a nucleus and are called as nucleons 

1. electron

   Nota:

   • Symbol e-   Mass (kg) 9.109 × 10-31   Approximate relative mass (a.m.u.) 0.0  Electric Charge -1 
2. neutron

   Nota:

   • Symbol  [n]   Mass (kg)  [1.675 × 10-27 ] Approximate relative mass (a.m.u.)   [1.0]   Electric Charge  [0] 
3. proton

   Nota:

   • Symbol  p+    Mass (kg)  1.673 × 10-27   Approximate relative mass (a.m.u.)   1.0 Electric Charge +1
4. electric & magnetic field

   Nota:

   •  The beam of electrons and protons are deflected when fired through electric or the magnetic field whereas the neutron are not deflected   This showed that both electrons and protons have charges   Electrons are lighter than proton because it deflected much more in the electric and magnetic field 

Nota:

•  Is the number of protons found in the nucleus of an atom   identical to the charge number of the nucleus    Atom is neutral particles. Hence, the number of protons in the molecules of an atom is the same as the number of electrons surrounding the nucleus   Example: atomic number of nitrogen (N) is 7. So nitrogen contains 7 protons and 7 electrons  The atomic number uniquely identifies a chemical element   So each element has different proton number that are arranged in an ascending order 

1. atomic number

Nota:

•  Total number of protons and neutrons present in the nucleus of an atom of an element   Nucleon number = Number of neutrons + Proton number = number of neutrons + atomic number 
• USES:  gives a useful rough figure for the atomic mass  Are used to identify isotopes  

1. mass number
2. A-Z

Nota:

•  Are atoms of the same element that contain the same number of protons but different number of neutrons   Have same chemical properties( because they are atoms of the same element) but different physical properties  Different isotopes of the same element cannot have the same nucleon number, but isotopes of different elements often do have the same mass number

1. stable

   Nota:

   •  Stable isotope will not disintegrate the nuclei spontaneously
2. unstable

   Nota:

   •  Unstable isotopes known as radioactive isotopes will disintegrate spontaneously to form a new nucleus (new element)   If the new nucleus that formed are also not stable, it will further decay until a new stable nucleus is obtained.   The disintegration of the isotope will emits electromagnetic waves  
   1. alpha
   2. beta
   3. gamma