Mass number is the total number of Protons and Neutrons. Simply subtract 85 from 210. 210-85=125 neutrons
In ions atoms lose and gain electrons
Valence electrons is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
The presence of valence electrons can determine the elements chemical properties, such as its valence—whether it may bond with other elements and, if so, how readily and with how many. In this way, a given element's reactivity is highly dependent upon its electronic configuration. For a main group element, a valence electron can exist only in the outermost electron shell; in a transition metal, a valence electron can also be in an inner shell.
An atom with a closed shell of valence electrons (corresponding to an electron configuration s2p6 for main group elements) tends to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive due to the relatively low energy to remove the extra valence electrons to form a positive ion. An atom with one or two electrons less than a closed shell is reactive due to its tendency either to gain the missing valence electrons and form a negative ion, or else to share valence electrons and form a covalent bond.
Similar to a core electron, a valence electron has the ability to absorb or release energy in the form of a photon. An energy gain can trigger the electron to move (jump) to an outer shell; this is known as atomic excitation. Or the electron can even break free from its associated atom's shell; this is ionization to form a positive ion. When an electron loses energy (thereby causing a photon to be emitted), then it can move to an inner shell which is not fully occupied.
When forming ions, elements typically gain or lose the minimum number of electrons necessary to achieve a full octet. For example, fluorine has seven valence electrons, so it is most likely to gain one electron to form an ion with a 1- charge.
Answer:
Direct relationship
Explanation:
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Chemical Reactions
Chemical changes take place when molecules or elements interact with other elements or molecules to form new chemical compounds. In order for a reaction to take place between molecules and or atoms, these molecules must come into contact with each other.
An example of a chemical reaction can be shown by the reaction of ammonia with hydrogen chloride to form ammonium chloride. This reaction is usually shown by a shorthand method called a chemical equation. The chemical equation for this reaction is...
NH3 + HCl � NH4Cl
This equation does not clearly show what has happened. In order for these two molecules to react, the pair of electrons on nitrogen must collide with the hydrogen atom of the hydrogen chloride on the side exactly opposite of the chlorine atom.
This collision must not only be precise as to the angle of the collision, it must have enough energy to break the bond between the hydrogen atom and the chlorine atom and form a new bond between the hydrogen atom and the nitrogen atom. Energy is released when a bond is formed. If all of these requirements are met, a reaction occurs forming a new compound.

The rate of a chemical reaction depends on all of the above factors. The reaction rate is measured by the change in concentration of one of the reactants or products over a measured period of time.
If some reaction condition is changed, the reaction rate will be changed.
Reaction coordinate diagrams are used to visualize the energy changes in chemical reactions. Some initial energy must be applied to any reaction in order to get the reaction started. This energy is called the energy of activation Ea.
If a reaction releases more energy than it takes to keep it going, it is called an exothermic reaction.

If a reaction requires a constant application of energy to keep it going, it is called an endothermic reaction.

A catalyst is something that, when added to a chemicalreaction, will increase the reaction rate without undergoing a permanent change. Although it appears that only Ea is lowered for a catalyzed reaction, the actual reaction pathway must change due to the involvement of the catalyst with the reactants. The energy released for the reaction remains the same. Catalysts are used extensively in biochemical reactions in order to decrease the energy demands for the animal or plant.

Matter can neither be gained nor lost in a chemical reaction. The number and type of atoms in the reactants must exactly equal the number and types of atoms in the products. The arrangement of the atoms will be different because new compounds are formed. Therefore, we must balance chemical equations with respect to the numbers of all of the atoms that are involved in the reaction.
