How is a molecule or polyatomic ion held together?
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just to add to what rb42rdsuns said-\n\nCovalent bonds are formed when atoms "share" electrons so that each nucleus "thinks" that it has, typically, 8 electrons in its valence (outer) shell.  This is typically a lower energy system, which is favorable.  When the two atoms are identical (for example, two hydrogens), the electrons are shared equally  between the atoms.  Sometimes one atom attracts the electrons "better" than the other atom, and this results in a polar bond, in which each of the two atoms has a slight charge.
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Atoms are the smallest pieces of an element that still exhibit that element's properties.  They consists of a nucleus (protons and neutrons) and  electrons.  A hydrogen atom doesn't even have a neutron.\nA molecule is a combination of atoms of at least two different elements.  These atoms share at least one electron through a covalent bond.  The molecule will exhibit some of the properties of each of its ingredient elements, as well as some of its own unique properties.\nA neutral atom or group of atoms has no charge. It is neither a positive nor negative ion.\nAn ion is an atom or group of atoms that has either more or less electrons than it has protons.  If its number of electrons is greater that its number of protons, then it has a negative ionic charge, in the amount of the difference.  If its number of protons is greater than its number of electrons, then it has a positive ionic charge, in the amount of the difference.
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If you could shrink 'way down and look at a single water molecule, you\nwould find that it is made of two hydrogen atoms and one oxygen atom.\nThey are arranged in a V-shape, with the oxygen at the point.  The result\nof this shape is that there is more negative charge at one end of the\nmolecule than the other (oxygen likes to have negative charge).  We call \nthis a POLAR molecule.\n\nOther polar molecules like salt and sugar and Kool-aid will dissolve in\nwater because the water molecule will be attracted to their charged ends.\nThe water molecule likes their charges so much that it will actually\nsurround the salt or sugar molecules, so that each one looks like a ball\nof water molecules.  We call this SOLVATION.  Since the salt molecule\nis surrounded now by water, it can't stick to other salt molecules, so\nit just sort of floats away.
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1)electron ...(also negative meson)\n2)the atom is the basic (many atoms make molecule and so on)\n3)polymer (the most famous are protiens)
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Ammonium (NH4+) is a polyatomic ion.  That means that it is composed of a group of atoms that are covalently bound together.  As a whole, that group has a charge of +1.  \n\nBecause this group of atoms has a charge, it is an ion, and can form ionic bonds with other ions.  So in summary, ammonium itself is a covalent compound, but it is able to form ionic bonds with other substances.
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Covalent bond: are those which one or more pairs of electrons are shared by two atoms.\nCovalent chemical bonds involve the sharing of a pair of valence electrons by two atoms, in contrast to the transfer of electrons in ionic bonds. These bonds lead to stable molecules if they share electrons in such a way as to create a noble gas configuration for each atom. \n\nHydrogen gas forms the simplest covalent bond in the diatomic hydrogen molecule. The halogens such as chlorine also exist as diatomic gases by forming covalent bonds. The nitrogen and oxygen which makes up the bulk of the atmosphere also exhibits covalent bonding in forming diatomic molecules. \n\n\n\nIonic Bonds\nIn chemical bonds, atoms can either transfer or share their valence electrons. In the extreme case where one or more atoms lose electrons and other atoms gain them in order to produce a noble gas electron configuration, the bond is called an ionic bond. \n\nTypical of ionic bonds are those in the alkali halides such as sodium chloride, NaCl\n\n\nThe below reference has some diagrams which are helpful as well.
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Gravity holds things with mass together.\n\nElectromagnetism holds things with unlike electric charges together.\n\nThe strong nuclear force holds things with colour charge together over short range.\n\n\nHope this helps!\nThe Chicken
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A complex molecule formed by the joining of many simple molecules is known as a Polymer(example as poly-ethene or polythene). Sorry, I don't know the latter part of your question.
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molecules are turned into ions....by an electron beam...\nions are separated according to their mass...by a magnet, deflection....\n\nmass spectroscopy can be used to study or analyse mixture of compounds....
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In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces.[1] Generally, a molecule is considered the smallest particle of a pure chemical substance that still retains its composition and chemical properties.[2] In the molecular sciences, a molecule is a sufficiently stable, electrically neutral entity composed of two or more atoms.[3] The concept of "monatomic molecule", i.e. a single-atom as found in noble gases, is used almost exclusively in the kinetic theory of gases.[4] Polyatomic ions may sometimes be usefully thought of as electrically-charged molecules.\n\nSee http://en.wikipedia.org/wiki/Molecules for more information.
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see the diagrams in the source\n\nBig Idea\nWater is comprised of two elements - hydrogen (H) and oxygen (O). Distilled water is pure and free of salts; thus it is a very poor conductor of electricity. By adding ordinary table salt (NaCl) to distilled water, it comes an electrolyte solution, able to conduct electricity.\n\nKey Concepts\n\n    * Ionic compounds such as salt water, conduct electricity when they dissolve in water.\n    * Ionic compounds consist of two or more ions that are held together by electrical attraction. One of the ions has a positive charge (called a cation) and the other has a negative charge (anion).\n    * Molecular compounds, such as water, are made of individual molecules that are bound together by shared electrons (i.e. covalent bonds).\n\nEssential Questions\n\n    * What happens to salt when it is dissolved in water?\n    * What are electrolytes?\n    * How can we determine the volume of dissolved ions in a water sample?\n    * How are atoms held together in an element?\n\nKnowledge and Skills\n\n    * Conduct an experiment to see that water can be split into its constituent ions through the process of electrolysis.\n    * Prepare and experiment with a 10% salt solution to better understand the process of ion exchange.\n    * Discuss and research the "softness" and "hardness" of water.\n    * Use the periodic table to identify elements and learn their characteristics.\n\nPrior Knowledge\n\n    * Define the difference between ionic and molecular compounds.\n    * Salt consists of sodium (Na) and chloride (Cl).\n    * Water is a tiny, V-shaped molecult with the molecular formula H2O.\n    * A basic understanding of how a battery works.\n    * Atoms are made of a positive nucleus surrounded by negative electrons.\n    * An atom's electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms.\n    * All matter is made up of atoms.\n    * Atoms of any element are alike, but different from atoms of other elements.\n\nCommon Preconceptions\n\n    * Students may think - "Water is a good conductor of electricity." Water is a very poor "conductor" of electricity. (The ionization constant for water is very small.) The reason it is dangerous to insert a light bulb while standing in a puddle of water is that water is a great solvent for ionic compounds. Tap water and fresh water typically contain dissolved ions in sufficient concentrations to enable the solution to be conductive. However, ions in solution carry the charge and are therefore responsible for the current, not the water itself.\n    * Students may think - "Electrons can flow through solutions." In "conduction of electricity" through solutions, electrons themselves do not pass through the solutions. Rather, the charge balance is maintained in the solution by movement of cations and anions toward the electrodes where charge transfer takes place at the solution interface.\n      Water is comprised of two elements - hydrogen (H) and oxygen (O). Distilled water is pure and free of salts; thus it is a very poor conductor of electricity. By adding ordinary table salt (NaCl) to distilled water, it comes an electrolyte solution, able to conduct electricity.\n\nConcept Map\nThis lesson and activity relates to the branch "Phases of Water" from the comprehensive Aquarius Concept Map - Water & its patterns on Earth's surface.\n\nBackground\nIn chemistry, electrolysis is a method of separating bonded elements and compounds by passing an electric current through them. An ionic compound, in this case salt, is dissolved with an appropriate solvent, such as water, so that its ions are available in the liquid. An electrical current is applied between a pair of inert electrodes immersed in the liquid. The negatively charged electrode is called the cathode, and th positively charged one the anode. Each electrode attracts ions which are of
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Protons, neutrons, and electrons.
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First one:\nA mixture is just a mix of many different things.  Think of chex mix.  You could pick out all the pieces and it would be easy.  I compound is held together by bonds and could not be separated easily.  \nSecond one:\nIonic.  Ionic compounds are held together by their opposing charges.  These charges would allow electricity to be conducted.  A molecular compound is when two atoms share electrons to fill up their orbitals.
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The strong force holds protons and neutrons together. Protons can't be in a nucleus alone, but the neutrons somewhat neutralize the charges between them so that a strong force can  hold the center together. There isn't really an answer of why this is, just like there isn't an answer to why there is gravity, or existance. But it's true that the only stable nucleuses are ones with roughly equal numbers of protons and neutrons, and the only nucleus comprised of only protons is hydrogen, made of one proton.
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Lets use the example of salt again. NaCl. What happens is this. Both water molecules and salt molecules are ionized molecules. When salt is added to water, the ionic bond breaks apart as the positively charged Na is attracted to the negatively charged OH in the water and the negatively charged Cl is attracted to the positively charged H in the water.
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There isn't one standard answer to this question.\nThe most common definition of a molecule is the smallest unit of a material that retains it's chemical attributes.\nmolecules interact with each other by electrostatic (electric) interaction :\n1. charged molecules interact by repulsion or attraction of monopoles.\n2. A charged and uncharged molecule interact by monopole-dipole interaction\n3. 2 uncharged molecules that have a permanent dipole interact by dipole/dipole interaction. A special case of this is hydrogen bonds between two hydrogen bearing molecules.\n3. molecules that do not posses dipoles interact by induced dipole/induced dipole interactions. An example of this is the formation of a solid from Argon atoms (molecules).
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Diatomic molecules contains two atoms (either same atoms or two different). Examples are, H2, O2, N2, Cl2, CO, NO etc.