Explain, in terms of atomic structure, why a potassium ion is smaller than a potassium atom.?
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When a Potassium atom becomes a Potassium ion, it looses a single electron to become K+.\nThe one electron it looses is located in its outermost, valance, electron shell (the S orbital).\nWhen this electron is taken away, the S orbital is empty and the radius of the resulting ion is now smaller than the previous atom.
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Here is the easy answer:\nCations are formed by losing electrons.  When comparing the relative numbers of electrons to protons, there will be more protons (because electrons were lost).  Protons are positively charged... since there are more of them compared to electrons, the cation will have a positive charge.
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K+; its a CATION because it carries a positive charge\nions that have a negative charge are called anions\n\nCa(+2): cation\nGa(+3):  cation\nN(-3): anion\nBr(-):  anion
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Well, it all depends on what kinds of atoms are involved.   For instance, a covalent bond between two atoms with very small radius is probably much greater than an ionic bond between two atoms with similar electronegative values.  What I mean is that comparing ionic and covalent bonds is a relative thing; there are many premises involved.
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Basic Atomic Structure\n\nThe definitions of atoms and elements seems, at first glance, almost circular: an element is a substance made up of only one kind of atom, and an atom is the smallest particle of an element that retains all the chemical and physical properties of the element. In fact, these two definitions do not form a closed loop, as they would if it were stated that an element is something made up of atoms. Every item of matter that exists, except for the subatomic particles discussed in this essay, is made up of atoms. An element, on the other hand, is—as stated in its definition—made up of only one kind of atom. "Kind of atom" in this context refers to the number of protons in its nucleus.\n\nProtons are one of three basic subatomic particles, the other two being electrons and neutrons. As we shall see, there appear to be particles even smaller than these, but before approaching these "sub-subatomic" particles, it is necessary to address the three most significant components of an atom. These are distinguished from one another in terms of electric charge: protons are positively charged, electrons are negative in charge, and neutrons have no electrical charge. As with the north and south poles of magnets, positive and negative charges attract one another, whereas like charges repel. Atoms have no net charge, meaning that the protons and electrons cancel out one another.
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Mendeleev's work in developing a periodic table showed that similarities among elements appeared with a certain regularity. As chemists developed ways to learn about the structure of atoms, it became apparent that this regularity could be explained on the basis of the arrangement of the electrons in atoms, especially the number of electrons most distant from the nucleus.\n\nThe arrangement of electrons helps explain the formation of different kinds of chemical bonds. Some bonds result from the donation of one or more electrons from one atom to another atom in the compound.Bonds of this type are called ionic, and compounds with bonds of this type are called ionic compounds. The component parts of ionic compounds are called ions. For example, sodium chloride is an ionic compound formed when electrons from sodium atoms move to chlorine atoms.The sodium atom is converted into a sodium ion with a positive charge.The chlorine atom is converted into a chloride ion with a negative charge.\n\nCovalent bonds are formed when electrons from two or more atoms are shared. Compounds formed in this way are called covalent compounds. Carbon tetrachloride is an example of a covalent compound. Four chlorine atoms surround a carbon atom. Each chlorine atom shares one of its electrons with the carbon; and, conversely, the carbon atom shares its electrons with the chlorine atoms.\n\nIn metals, the atoms are closely packed together in rows and layers. These rows and layers explain why metals are easy to bend. The loosely-bound outer electrons in metal are shared among many atoms, creating a ìseaî of negative charges holding the metal ions in place. This is called metallic bonding. The type of bonding, whether ionic, covalent, or metallic, determines the properties and the ways in which we use substances!\n\nChemical reactions occur when the atoms are taken apart or rearranged. Energy is conserved in such reactions;that is, the energy of the reactants is equal to the energy of the products.\n\nChemical reactions proceed at different rates. Some, such as the rusting of iron, proceed slowly. Others, such as the burning of methane gas, proceed rapidly. Temperature, surface area, air pressure, and the presence of moisture or catalysts are all conditions that affect the rates of chemical reactions. Catalysts are substances that increase the rate of a reaction but are not changed themselves when the reactions are complete.\n\nHuman understanding of these principles of chemistry has enabled us to make hundreds of thousands of useful products, which enhance our lives greatly.
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Energy level is much more significant to atomic size.
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interesting answer above.\n\nCarbon has 4 valance electrons which because of the relatively small size of the atom can move about and create all sorts of hybrid orbitals and molecular bonding orbitals allowing it to suit the bonding needs of many other atoms, thus making many varied combinations.\n\nIt is also in the middle range of electronegitivities therefore resisting in most situations becoming an ion.
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for cations the radii become smaller\nfor anions the radii become larger
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Not exactly sure what you're asking here either, but perhaps a better answer is that electrons that are shared equally between two atoms in a bond are covalent, while electrons that spend more time with one atom than with the other form an ionic bond.\n\nHope that helps.
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In Greek atomic theory, the atom was considered the smallest, indivisible, particle of matter.\nThey view atoms as the basic building block of everything else, and all atoms were identical, different combinations of how they were put together determined the properties of the substance.\n\nOf course, we now know that atoms themselves are made up of smaller, sub-atomic, particles, which are then intern made up of even smaller particles.  Atoms are the smallest particles of a given element which will exibit the properties of that element.  Different elements, and thus different types of atoms, exist.  So the Greeks were not correct in that respect.
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It isn't. the magnesium ion has a radius of 0.85 angstroms while the sodium ion has a radius of 1.16 angstroms.
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Most professional papers that I read refer to it as just water ion (in its charged form).  This a water molecule with an over-all positive charge.  I do not believe that its structure is known, but I could be wrong about this.\nSee example reference below:
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Most likely lost from both S and P subshells but two electrons parked in a D or F subshell associated with one main quantum number lower. Ions want to achieve a noble gas configuration, which means no or all electrons of the same main quantum number S and P orbitals filled.
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b and d are not right.\n\nb. - going across a row the atoms get smaller so Co is smaller than Fe\nd  - Na is in row 3 and is larger than Be and Ne which are in row 2
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If you think of the radii of the orbitals as being rungs in a ladder, the rungs get closer together as you go up the ladder (get further away from the nucleus of the atom).  The reason why they get closer together is simply as there are more stable standing wave formations for electron orbitals the further you get away from the nucleus.\n\nThis is why the size of the atoms slow down in their increasing as you go down any group, not just the alkali metals.
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cations form when the atoms lose an electron or more and have + valency , so the mass will decrease and the effect of the nuclei on the remaining electrons will be stronger so it attracts them stronger toward the center so the size will decrease .. while in the anions the number of electrons increase so the attraction caused by the nuclei is weaker so the size is larger ..\n\nsize of the cation of an element < size of the atom of that element < size of the anion of that element