What are atoms?
what determines an atoms reactivity?
what determines an atoms identity?
what are valence electrons?

The smallest particle of a chemical element can be defined as an atom.

Explanation:

The number of protons in one atom of an element determines the atom's identity, and the number of electrons determines its electrical charge.

a single electron or one of two or more electrons in the outer shell of an atom that is responsible for the chemical properties of the atom is known as valence electrons.

An atom's reactivity is its tendency to lose or gain electrons. ... This is because they have one outer electron and losing it gives them the stability of a outer electron shell as the next level... The reactivities of elements can be predicted by periodic trends.

Hope this helps! :^)

Explanation:

Atoms are the basic building blocks of ordinary matter. Atoms can join together to form molecules, which in turn form most of the objects around you.

The number of protons in one atom of an element determines the atom’s identity, and the number of electrons determines its electrical charge.

Valence electrons: an electron of an atom, located in the outermost shell (valence shell) of the atom, that can be transferred to or shared with another atom.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.