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-   -   Atoms, ions etc. (https://www.askmehelpdesk.com/showthread.php?t=321784)

  • Feb 25, 2009, 02:31 AM
    XM8
    Atoms, ions etc.
    Hello,

    We're studying something about monatomic ions, but first of all I'd like to ask something about ions in general.

    Now I'm not so sure what an ion is, am I correct in thinking that an ion is an atom that has lost or gained an electron?

    In that case it would be different than an isotope which is an atom with a different number, A, of nucleons, right?

    We've started "stability of monatomic ions" today and I'd just like to clear up a few things.

    Why must an atom, let's say sodium, Na+, remove one of it's 11 electrons to be stable?

    My teacher said that "stable elements" are elements that one finds in nature, e.g. Hydrogen but is sodium a natural chemical element? What about Mg²+?

    I understand the business about 1 electrons being moved to another, and how to write that down and stuff, but I don't understand the reason why.

    Why must one atom give 1 electron, or more to another atom to be "stable". Is it just to have an even number?


    Thanks,

    -Xm8
  • Feb 25, 2009, 06:07 AM
    Perito
    Quote:
    Originally Posted by XM8 View Post
    Now I'm not so sure what an ion is, am I correct in thinking that an ion is an atom that has lost or gained an electron?
    Pretty close. It can also be a cluster of atoms like "SO4(-2)" (sulfate).

    Quote:
    Originally Posted by XM8 View Post
    In that case it would be different than an isotope which is an atom with a different number, A, of nucleons, right?
    That is correct.

    Quote:
    Originally Posted by XM8 View Post
    Why must an atom, let's say sodium, Na+, remove one of it's 11 electrons to be stable?
    The lone electron in the "S" shell is at a very high energy level. In order to drop down into a lower energy state, it gives up one of its electrons.

    Quote:
    Originally Posted by XM8 View Post
    My teacher said that "stable elements" are elements that one finds in nature, e.g. Hydrogen but is sodium a natural chemical element? What about Mg²+?
    Na+ and Mg²+ are both naturally occurrng. Salt, NaCl ionizes and is very prevalent in seawater. MgCl2, which also ionizes is similarly found in seawater and other brines. Hydrogen gas, H2, exists, but it isn't an ion (note that it doesn't exist as "H"). Acids like HCl (hydrochloric acid) exists in the stomach. Acids disassociate into H+ and Cl-

    Quote:
    Originally Posted by XM8 View Post
    I understand the business about 1 electrons being moved to another, and how to write that down and stuff, but I don't understand the reason why.
    It all has to do with electrons being in high-energy states. If it can move into a lower energy state (by reacting), it will happen.

    Quote:
    Originally Posted by XM8 View Post
    Why must one atom give 1 electron, or more to another atom to be "stable". Is it just to have an even number?
    This is mostly empirical, though it is also due to energy. Think of it as empirically-determined information. The Periodic Table of the Elements is your best friend in figuring out how many electrons an element will lose or gain. Elements in group 1A (H, Li, Na, K, Rb, Cs, Fr) invariably lose just one electron. Elements in groups 2A (Be, Mg, Ca, Sr, Ba, Ra) lose two electrons. As you go down in the group, the tendency to lose lessens.

    On the right-side of the periodic table, the halogens (group VIIA), (F, Cl, Br, I, At) gain one electron to fill their last "shell".

    All compounds that can form ions can exist as neutral, uncharged, pure elements. Many of these elements, however, are very reactive with the air. Elements in groups 1A are very reactive. That's why you don't find pure Na in nature. You always find sodium in compounds. We say that it is in its +1 oxidation state.
  • Feb 26, 2009, 10:46 PM
    bellakity
    Quote:
    Originally Posted by XM8 View Post

    I understand the business about 1 electrons being moved to another, and how to write that down and stuff, but I don't understand the reason why.

    Why must one atom give 1 electon, or more to another atom to be "stable". Is it just to have an even number?



    -Xm8

    Think of it like this:

    The atoms want a full outer shell (to become like the noble or inert gases), the first shell (K) can hold 2 electrons, the second (L) can hold 8, the third (M) can hold 8 and so on. The elements on the left side of the periodic table (metals) want to loose electrons because its easier (loose 2 instead of gaining 6) and the elements on the right (non-metals) want to gain the electrons (gaining 2 is easier than losing 6). The number of electrons the element wants to loose/gain can be determined using the periodic table, group I has a valency of +1 (loose one electron (elements normally have an equal number of protons and electrons, when an atom looses or gains an electron it becomes an ion and has a charge) the overall charge is +1 because there is one more proton than electron) group II +2, group III +3, group IV 4 (doesn't make much difference, it can gain 4 electrons or loose 4 electrons) group V -3, group VI -2, group VII -1 and group VIII 0 (noble/inert gases, already have a full outer shell.) when they have a full outer shell they are stable and won't react in a chemical reaction (that's why you rarely have elements such as He, Ne, Ar in chemical reactions). Elements can also 'share' electrons like oxygen - O2, or hydrogen - H2.


    Hope that helps (and makes sense)

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