The bonding of elements occurs in one of two ways, by electrostatic attraction of ions (Ionic Bonding) or by formation of electron orbital interactions that favor electron pairing of valence level electrons (Molecular or Covalent Bonding). The formation of the ionic bond or covalent bond is typically related to 'Periodic Trends' associated with elements in series (horizontal rows of elements) or in groups (vertical columns of elements). The periodic trends are defined in terms of three characteristics of the elements:
1. atomic &/or ionic radii,
2. the energy required to remove (ionize) valence electrons (Ionization Energy), and
3. an elements affinity (attraction) for gaining electrons into the valence level atomic orbital (Electron Affinity).
For elements to undergo reaction, one must consider the natural processes that drives the interactions of elements. In general, the process of bonding is preceded by the element undergoing a change in structure so that the elements of interest will favor the formation of the bond; i.e., Ionic or Molecular Bonding. The process is generally described as the 'Octet Rule' which states
"Elements during the chemical bonding process tend to lose or gain electrons at the valence level in order to achieve a Noble Gas electronic configuration"; or, a pseudonoble gas configuration if considering transition metal elements.
It is suggested that the students new to this topic consider the pre-bonding process in terms of 'ease of formation' of the atomic structures involved in the bonding process. That is ...
Element =(ease of formation)=> Pre-bonding Atomic Structure (ions or pre-bonding orbital structures).
Beyond this point, discussion of the three factors affecting reactivity of elements is extensive to say the least. It is suggested that one consult a current survey course General Chemistry textbook (preferably college level) and review the topics given in the introduction. To understand the nature of chemical bonding, these topics need to be reviewed in detail as they are the foundations needed.