IGCSE Chemistry - Atom notes

Atom:

Particle Relative mass Relative charge


Proton (p) 1 +1

Electron (e) 1/1840 -1

Neutron (n) 1 0



 Number of protons + number of neutrons = atomic number (nucleon number)
 Atomic number is the number of protons and neutrons in the nucleus of an atom
 Isotopes are atoms of the same element having the same atomic structure but different
atomic mass (different number of neutrons)




 Valency:
 Number of electrons that an atom of an element loses/gains or shares to attain the
configuration of the nearest noble gas (to gain stability)


 In the periodic table, the elements are arranged in the increasing order of their numbers
 The vertical column are called groups
 The groups denotes the number of valence electrons
 The horizontal rows are called periods
 The period number denotes the number of shells in an atom
 Elements changed from metals to nonmetals as we go from left to right
 Metals lose electrons to form positive ions
 Nonmetals gain electrons to form negative ions
 Metals have 1,2, or 3 valence electrons
 Non-metals have 4,5, or 6 valence electrons