why are there just two hydrogen atoms in molecule?
963196
Many molecules have a lot more than two. You just have to keep counting. Don't forget the green ones.
222974
Two hydrogen atoms, one oxygen atom.  H2O
325448
for one molecule of H2O, there will be one molecule of H2 and one molecule of O.\n\nfor one molecule of H2O, there will be two atoms of H and one atom of O.
285141
All moleciles do not contain multiple bonds.\n\nIonic bonds are usually single bonds.\n\nMore than one bond may be indifferent manners.\nIn case of H2O oxygen forms one bond with each hydrogen and thus there are two bonds.\n\nIn case of O2 molecule the two oxygen atoms form a double bond with each other.\n\nMore than one bond (as H2O) or a multiple bond (as O2, N2, H2C=CH2) depend on the valency number of the atoms.
223089
its just two atoms- one hydrogen and one florine, so you have already written the molecular formula.  HF is closely related to HCl (hydrochloric acid) because Cl and F are closely related elements.  But, HCl is a much stronger acid, because it releases from H more easily than F, and HF is special in that its the only acid that can etch glass.
180938
ex: 2 hydrogen atoms and 1 oxygen atom combine to create 1 molecule of H20(a chemical change).
893002
It's because of the H-bonding of water molecules (18g/mol). H-bonding is stronger than Van der Waals forces - for example in methane CH4 (16g/mol), which is gas at room temperature. Besides, water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of H-bonds of a water molecule is up to four. Unlike in ammonia NH3 (17g/mol), there's only one H-bond since nitrogen has only one lone pair. Consequently, its melting and boiling points are lower than water (ammonia is also gas at room temp).
231898
There are a few isomers possible.\n\nEssentially there are two C's double-bonded, with either 2H's off one C and 2Br's off the other C.\nOr 1H and 1Br off each C
905720
Diatomic molecules are molecules formed of two atoms, of the same or different chemical elements. The prefix di- means two in Greek. Diatomic elements are those that almost exclusively exist as diatomic molecules, known as homonuclear diatomic molecules in their natural elemental state when they are not chemically bonded with other elements. Examples include H2 and O2. Earth's atmosphere is comprised almost completely (99%) of diatomic molecules which are oxygen (O2) (21%) and nitrogen (N2) (78%). The remaining 1% is predominantly argon (0.9340%)\n\nOxygen also exists as the triatomic molecule ozone (O3).\n\nThe diatomic elements are hydrogen, nitrogen, oxygen, and the halogens: fluorine, chlorine, bromine, iodine, and astatine. Astatine is so rare in nature (its most stable isotope has a half-life of only 8.1 hours) that it is usually not considered. Many metals are also diatomic when in their gaseous states.\n\nThe bond in a homonuclear diatomic molecule is non polar and fully covalent. Examples of heteronuclear diatomic molecules include carbon monoxide (CO) and nitric oxide (NO).\n\nOther elements exist which form diatomic molecules but with high instability and reactivity. An example is diphosphorus.
950410
Mainly H-bonding (intermolecular forces)
608500
Group of atoms form a molecule.\n\nA molecule can be made of two or more atoms. This atoms can be of the same type:\n\nCl2, H2, O2...\nO2= an oxygen molecule. It is made of two equal oxygen atoms\n\nOr of different types:\n\nCH4, HCl, NH3...\nCH4 = a methane molecule. It is made of 1 atom of Carbon and 4 equal atoms of hydrogen
461
Without checking astronomical data, I'll try the chemical approach:\n\nThe most abundant elements in the universe are hydrogen (with a big lead) and most of the other light elements, so we have to look for the most probable triatomic molecule we can form from light elements.\n\nThis makes H2O my prime candidate, being the most stable molecule to contain two hydrogen atoms. HCN or CO2 have a much lower probability. SiO2 is pretty abundant, but not as distinct molecules.
695499
B and C.  Molecules with H bonded to N, O, or F can form hydrogen bonds.  Others cannot.  In molecules A and D, all the H's are bonded to C's, so they are not capable of hydrogen bonding.  In molecules B and C, there is an O-H bond, so they are capable of hydrogen bonding.\n\nAlthough all four structural formulas have H written next to O, that doesn't necessarily indicate that there is an O-H bond.\n\nMolecule A is an ether, so the oxygen is between two carbons.  Specifically, it's dimethyl ether, so there's a methyl group (CH3) on each side of the oxygen.  You can find a picture of it here: http://en.wikipedia.org/wiki/Dimethyl_ether\nThe oxygen in an ether doesn't allow for hydrogen bonding because none of the hydrogens are attached to it.\n\nMolecule B a carboxylic acid.  Specifically, it's acetic acid.  It consists of a methyl group attached to a carboxyl group, which is a carbon double bonded to an oxygen and also single bonded to an OH group.  The O-H bond in the carboxyl group allows the molecule to form hydrogen bonds.\nYou can find a picture of its structure here:\nhttp://en.wikipedia.org/wiki/Acetic_acid\n\nMolecule C is ethanol.  It consists of a methyl group, a methylene group (CH2), and an OH groupl.  Like with carboxylic acid, the O-H bond is capable of hydrogen bonding.\nHere's it's structure:\nhttp://en.wikipedia.org/wiki/Ethanol\n\nMolecule D might be a bit misleading at first glance, but it's actually an aldehyde, specifically acetaldehyde.  It consists of a methyl group bonded to a second carbon that is bonded to a hydrogen and double-bonded to an oxygen.  That last hydrogen is attached to the carbon, rather than the oxygen, so it can't do hydrogen bonding.  Here's a picture of it's structure:\nhttp://en.wikipedia.org/wiki/Acetylaldehyde
554160
A molecule is polar when it has a dipole moment that does not cancel out. For example, consider the molecule CH4 (methane) which is nonpolar. It has a carbon atom bonded to 4 hydrogen atoms. Bonding is the overlap of the electron density. So you have an electron from a hydrogen and an electron from the carbon forming each of the bonds. Carbon is just very slightly more electronegative (tendency of pulling electrons closer to itself) than hydrogen. This means that the electrons are pulled by carbon away from hydrogen, but not by much (the difference is very very small). This shifting of electron density allows for the carbon to be slightly more negatively charged and hydrogen slightly electron deficient. This makes the C-H bond just slightly polar. However, because there are 4 hydrogen atoms that are bonded to the carbon, this bond polarity cancels each other out...meaning that the bonds are slightly polar, but the overall molecule is nonpolar. \n\nTo determine if the bonds are polar you just have to know the electronegativity differences. To know if a molecule is polar, you must know the correct geometry. Since electrons are negatively charged and repel each other, they want to be as far away from each other as possible. If you have a carbon bonded to 4 hydrogens, you will have a tetrahedral geometry with the hydrogens 109.5 degrees apart from each other creating the best possible arrangement. Also, if you have a lone pair of electrons, then the molecule will always be polar because of that charge separation.
263220
1 but it prefers two, as do all atoms prefer to mimic the noble gases.  For instance, if a hydrogen is in a bond it actually has two electons that orbit its nucleus.
682608
The hydrogen atom attracts more electrons than the oxygen atoms do. It's uneven.
195032
Because you have 3 hydrogen atoms one oxygen and one cl.