[Fembot]

What would you say is the part of the atom that is responsible for chemistry

[schoolkid323]

the protons

[Yggdrasil]

What are chemical bonds composed of?

Also, why might Na_(s), a metallic solid that reacts violently with water, have such different chemical and physical properties than Na⁺_(aq), a common and very inert cation?

[Mitch]

the protons

Not the best choice. Protons don't participate in the chemical bonding in molecules.

[mahi123]

its electrons obviously.

[Fembot]

Aren't the Protons just as important as the electrons?? I thought that together they give energy by repeling off of each other?

[Borek]

Number of protons in nucleus makes the element - but electrons are responsible for its chemistry.

[Yggdrasil]

In all of chemistry (except for nuclear chemistry) we don't do anything to change the nucleus.  All that chemical reactions do is to rearrange electrons (by making or breaking chemical bonds).  While the number of protons in an atom helps to determine some of its properties (partly by modulating the number of electrons), understanding the electronic structure of atoms and molecules is key to understanding their chemical properties and reactivity.

Think of it this way.  If you were an atom and you were approaching another atom what would you see and interact with first, the electrons of that atom or its protons?