The power is known as Van der Waals force. Atoms become more stable when their outermost electron shells are emptied out or filled up. This means that __________. increases the oceanic concentration of carbonic acid It means lacking affinity for water, and tending to repel or not to absorb water. By lacking a charge, these molecules do not have any charge-to-charge interactions that will allow them to interact with water. Which property of water is most directly responsible for the ability of sweat to lower body temperature? Here, we should consider the fact like dissolves like. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. Now you have check out why RideWrap's hydrophobic protective film benefits your bicycle and you. Why does adding a little dish detergent (soap) help to remove the grease from dirty dishes better than water alone? To view the purposes they believe they have legitimate interest for, or to object to this data processing use the vendor list link below. Hydrophobic Molecules: When hydrophobic molecules are added to water, the entropy is decreased. A Hydrophilic ; B Hydrophilic C. A Hydrophilic ; B Hydrophobic, Biologydictionary.net Editors. An example of a hydrophobic group is the non-polar methane molecule. Moreover, the formation of clumps causes the entropy of the system to decrease. If a molecule has areas where there is a partial positive or negative charge, it is called polar, or hydrophilic (Greek for "water-loving"). Hydrophilic Molecules: Hydrophilic molecules are called hydrophiles. These molecules have nonpolar covalent bonds or polar covalent bonds, both of which share their electrons equally between the bonded elements. This type of mixture is called a colloid. Difference Between Hydrophobic and Hydrophilic Molecules, What is the Difference Between Hydrophobic and Hydrophilic Molecules. This happens mainly due to the polarity of water molecules. Bonds between carbon atoms share electrons equally, and no static electrical charge is created. The fatty acid tails can easily interact with other nonpolar molecules, but they interact poorly with water. Calculate the power dissipation and the power factor for frequencies of Which amino acid is the most hydrophobic? This is how cell membranes are formed the water-fearing parts of the molecules all face the same direction and squeeze together to prevent water from touching them. When a soap micelle encounters oil or grease, these non-polar materials are forced to the inside of the micelle to get away from the polar water and polar heads of the micelle, where they are trapped. CH3CH2CH2CCl3\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { CH } _ { 2 } \mathrm { CCl } _ { 3 }CH3CH2CH2CCl3, The amount of heat required to change the temperature of 1 g of any substance by one C is defined as. Hydro phobic and hydro philic are opposites. Water is the most commonly known example of polar molecules in the world, and it has polar nature, which means that it bonds with many other molecules. To study the synchronous removal mechanisms of hydrophilic organics 2,4-di-tert-butylphenol and 2-palmitoyl-rac-glycerol and the hydrophobic organics n-octadecane and 2-stearoyl-rac-glycerol coexisting in the biochemical effluent of coal gasification processes treated by a semicoke-polysilicate aluminum ferric sulfate (PSAFS) process, the fitting results of the D-R adsorption isotherm model . Therefore, the value of G should be a large positive value. Thus, a water moleculea polar moleculeis unable to establish an association with the non-polar chemical group. Watch the video to see how it will look. Here the electrons are divided equivalent to no electrical charge difference between them. Proline is clearly nonpolar though. Since new bonds are formed between hydrophiles and water molecules, this mixing is exothermic. Most acid precipitation results from the combination of _____ with water in the atmosphere, forming strong acids that fall with rain or snow. Cell membranes are made of macromolecules known as phospholipids. e.. "Hydrophilic." Now understand the meaning of phobia. When both hydrophilic and hydrophobic parts are present in a structure it is called as what? This property causes water molecules to be weakly attracted to other water molecules (positive to negative, negative to positive) and results in the cohesion of water to itself. Functional groups are usually classified as hydrophobic or hydrophilic depending on their charge or polarity characteristics. According to the chemistry of hydrophilics, it means that these are the molecules that love water, or we can say that they can mix with water. We also have to realize that if it is water-fearing, it will not interact with water molecules because it is unfavorable. Wow! Atoms that carry a charge, either positive or negative, are called ions and, because opposites attract, they can form an ionic bond. When they are exposed to water, their nonpolar nature disrupts hydrogen bonds between water molecules, forming a clathrate-like structure on their surface. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. The cookies is used to store the user consent for the cookies in the category "Necessary". Accessed 20 Sept. 2017. Hydrophilic molecules tin can bind with h2o, and thus they make up substances that tin can deliquesce in water. H2o is not . Why was Copernicus reluctant to publish his ideas? What is the difference between hydrophilic and hydrophobic molecules? What property of water best explains this phenomenon? This cookie is set by GDPR Cookie Consent plugin. Are lipids hydrophobic or hydrophilic? So essentially, hydrophobic molecules are molecules that do not have a charge, meaning they are non-polar. A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added. Diffusion is a very important property of most hydrophilic substances to living organisms. Nonpolar molecules are hydrophobic; hydro- means water and -phobic means fear. What happens when you mix a hydrophobic substance with water? Without a channel through the hydrophobic membrane, the hydrophilic substances could not pass. Molecules such as oil and petrol are nonpolar in chemistry. both sentences are true both sentences are false the first sentence is true; the second is false the first sentence is false; the second is true QUESTION 3 Which of the following is a hydrophilic polar covalent molecule? The folding of proteins is very important because of the hydrophobic interactions that provide an . Hydrophobic - Molecules or substances that are not attracted to water, or repel it. Here, the hydrophilic part is directed to the outside because hydrophilic part attracts water. Explain. In a polar bond, the electrons cannot share equal distribution. A good example of this would be a cell membrane. This property of water was important for the evolution of life. And conversely, you have the polar ones. A pH of 6 is how many times more acidic than a pH of 9? The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. By clicking Accept All, you consent to the use of ALL the cookies. Nonpolar and polar covalent bonds differ on the basis of whether they share electrons equally or unequally. The molecules are then distributed to areas of low concentration, where more water molecules can interact. The polar nature of water molecules allows other polar and ionic substances to dissolve easily in water, The polar nature of water molecules attracts hydrophobic . In fact, oils are hydrophobic, or "water fearing." Instead of being attracted to water molecules, oil molecules are repelled by them. Some other molecules are between the polar and nonpolar molecules. Oils and fats are hydrophobic. Proteins determine most of the membrane's specific functions. The heads of the soap micelles are polar and the tails, which face inward to retreat from the polar water, are non-polar. Put a few drops of vegetable oil inside the loop of thread and gently stir the oil. These substances lack the ability to hydrogen bond and their surface free energy is relatively low. At the molecular level, salt dissolves in water due to electrical charges and due to the fact that both water and salt compounds are polar, with positive and negative charges on opposite sides in the molecule. Which property of water is most directly responsible for the ability of sweat to lower body temperature? The relative attraction of an atom to an electron is known as its electronegativity. Hydrophilic Molecules: Hydrophilic molecules are polar. Chemical Bonds: Atoms seek more stable states. Hydrophobia: 1. But all compounds in nature do not mix with water. Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. How are bridges built over larger bodies of water? These hydrophilic molecules are called hydrophiles. This cookie is set by GDPR Cookie Consent plugin. Lipophilic portions are hydrophobic and nonpolar. Hydrophobic molecules form a micelle that looks like a clump in shape to have a slight . You can fill a glass of water to just slightly above the rim without it spilling over the glass. However, an amphiphile may have several hydrophilic and lipophilic parts. Mar 16, 2014. The lipophilic section is usually a hydrocarbon moiety, consisting of carbon and hydrogen atoms. There is a force between nonpolar molecules that is very weak and gets attracted to each other. Explain your reasoning. The head of the phospholipid molecule is the hydrophilic region. These cookies will be stored in your browser only with your consent. Nonpolar molecules occur when electrons are shared equal between atoms of a diatomic molecule or when polar bonds in a larger molecule cancel each other out. Will a precipitate of solid Ag2CrO4\mathrm{Ag}_2 \mathrm{CrO}_4Ag2CrO4 form in solutions 2-4? Water molecules have __________ than molecules of similar size, such as ammonia and methane, reflecting its capacity to absorb large amounts of heat. The folding of proteins is very important because of the hydrophobic interactions that give an explanation for the hydro Download the App! The first group includes the nonpolar amino acids, and then the second group includes the polar ones. You also have the option to opt-out of these cookies. Some hydrophilic substances do not dissolve. Hence, the dissolving of hydrophobic molecules in water is non-spontaneous. Therefore, hydrophilic substances should be polar in order to dissolve in water. Nonpolar - Molecules that distribute electrons evenly, causing no interaction with polar molecules. The reason for the confusion is that are there several ways to define and measure polarity and hydrophobicity for amino acids. are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively, The amount of energy that must be absorbed or lost to raise or lower the temperature of 1 g of liquid water by 1C _____, Because organisms are made primarily of water, they resist rapid temperature changes. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. Adding a base tends to __________ of a solution. They are described as hydrophobic, or water fearing. Methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and t-butyl alcohol are all miscible with water. If a molecule is water-loving, it is known as hydrophile (noun) that possesses a hydrophilic nature. Is amino hydrophobic or hydrophilic? Why and how does lateral transfer occur in so many species? Salt is a hydrophilic molecule which dissolves in water very easily because of its charges ions . Hydrophobic. Proteins become functional enzymes when they are the right shape to accept a substrate and lower the activation energy of a chemical reaction. Water molecule consists of two hydrogen atoms and one oxygen atom. the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule. Which statement helps to explain why ice is less dense than liquid water? Hydrophobic molecules and surfaces repel water. The ability of water molecules to form hydrogen bonds with other water molecules and water's ability to dissolve substances that have charges or partial charges are __________. Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. This is because oil is made up of nonpolar molecules. When placed in water, hydrophobic molecules tend to form a ball or cluster. The fatty acids in the lipid bilayer are non-polar and. A long string of amino acids becomes folded because of the various interactions it has with the other amino acids in the chain, as well as interactions with the environment. So does the Earth. Polar molecules occur when there is an electronegativity difference between the bonded atoms. Because polar molecules are generally water soluble, they are referred to as being hydrophilic, or water-loving. This website uses cookies to improve your experience while you navigate through the website. Non-polar molecules do not dissolve in water as they cannot form hydrogen bonds, and so they are hydrophobic. Although water cannot easily pass through the cell membrane, there are many embedded proteins that allow water into the cell. Difference between Hydrophilic and Hydrophobic. If the arrangement is symmetrical and the arrows are of equal length, the molecule is nonpolar. This is how cell membranes are formed -- the water-fearing parts of the molecules all face the same direction and squeeze together to prevent water from touching them. Sugar, sodium chloride, and hydrophilic proteins are all substances that dissolve in water. In other words, we can say the nonpolar molecules repel water because it is hydrophobic. Are nonpolar molecules hydrophobic or hydrophilic? The cookie is used to store the user consent for the cookies in the category "Performance". Do Men Still Wear Button Holes At Weddings? Webnews21 is all about lifestyle and entertainment. We also use third-party cookies that help us analyze and understand how you use this website. The partial charges on a water molecule occur because of __________. Hydrophobic Molecules: Hydrophobic molecules are called hydrophobes. Conversely, nonpolar molecules do not dissolve readily in water and are hydrophobic. Is oil hydrophilic or hydrophobic? We know that carbon bonds with oxygen, and there is a double bond structure. ", Biologydictionary.net Editors. The word stem hydr comes from the greek hydor meaning water, therefore hydrophobic materials are water-fearing , and do not mix with water, whereas hydrophilic materials are water-loving and have a tendency to be wetted by water. So essentially, hydrophobic molecules are molecules that do not have a charge, meaning they are non-polar. C REASON: definition of a polar molecule (uneven sharing of electrons; more electronegative leads to strongly pulling more shared electrons towards itself) Water moves up a plant because of hydrogen bonds by a process called __________. The polar nature of water molecules repels hydrophilic compounds, preventing dissolution. Other nonpolar molecules include carbon dioxide (CO2) and the organic molecules methane (CH4), toluene, and gasoline. Her interest areas for writing and research include Biochemistry and Environmental Chemistry. These molecules have nonpolar covalent bonds or polar covalent bonds, both of which share their electrons equally between the bonded elements. This means when hydrophobic items come in contact with liquids, water is encouraged to bead up and roll off the surface- almost pushing it away like a magnet pushes away metal objects. Whats the difference between polar and nonpolar? The difference between Hydrophilic and Hydrophobic materials is that the hydrophilic materials are water-loving or water attractive. Because nonpolar molecules do not easily dissolve in water and are hydrophobic, they become squeezed together. The term phobia means fear from water. But opting out of some of these cookies may affect your browsing experience. The interior parts of the protein that interact with the lipids in the middle of the membrane, will be hydrophilic. Like water sucrose molecule forms bond between oxygen and hydrogen atom and electron is charged between these atoms to form a covalent bond . In both molecules, you have to remember that there will be a covalent bond. The essential point of nonpolar is that it can form by identical molecules. It does not store any personal data. Many macromolecules are amphiphilic in this way, to interact with various substances. The amount of heat required to convert 1 g of any substance from the liquid to the gaseous state is defined as __________. The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. Nonpolar molecule are water fearing and do not easily dissolve in water. An AC voltage with an amplitude of $100 \mathrm{~V}$ is applied to a series combination of a $200-\mu \mathrm{F}$ capacitor, a $100-\mathrm{mH}$ inductor, and a $20.0-\Omega$ resistor. Because glucose is a partially hydrophilic molecule, it dissolves equally into the bloodstream and provides glucose to all parts of the body. What property does each part display? How did the Soviets take over Afghanistan? Oils, fats, and certain organic solvents do not dissolve in water because they are hydrophobic. If we learn about hydro, then it means water. Now we will discuss what nonpolar molecules are, and then we will explain to you about hydrophobic molecules to understand that nonpolar substances are hydrophobic. The side chains within the core are tightly packed and participate . We'll come back to these examples later. In areas of high concentration of the molecules, water moves in and pulls the molecules apart. Nonpolar molecules are those that aren't polar. These amino acids can be hydrophilic or hydrophobic. Because nonpolar molecules do not easily dissolve in water and are hydrophobic, they become squeezed together. What are Hydrophobic Molecules Definition, Properties, and Examples 2. However, you may visit "Cookie Settings" to provide a controlled consent. Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. A hydrophilic molecule or portion of a molecule is one whose interactions with water and other polar substances are more thermodynamically favorable than their interactions with oil or other hydrophobic solvents. increases the hydrogen ion concentration in the oceans but decreases the carbonate ion concentration and threatens the livability of the oceans for calcifying organisms Water can interact with these dipoles, and dissolve glucose. Hydrophilic Molecules: Dissolving hydrophilic molecules in water is an exothermic reaction. They interact with other non-polar molecules in chemical reactions, but generally do not interact with polar molecules. Nonpolar molecules that repel the water molecules are said to be hydrophobic; molecules forming ionic or a hydrogen bond with the water molecule are said to be hydrophilic. As seen in the graphic below, these proteins often function by using the energy from ATP to move various substances across the membrane. What is salt? A. Hydrophilic B. Hydrophobic C. Nonpolar, 2. These residues typically form the hydrophobic core of proteins, which is isolated from the polar solvent. cause hydrophobicity. Nonpolar molecules that cluster away from water molecules are called __________ molecules. Matt, lipids: phospholipids are an example because their "head" is In polar molecules, the numbers of electrons are not equally divided. The salt draws the water out of the potatoes, due to the strong attraction between the ion molecules of salt and the polar regions of the water molecules. Literally, an irrational fear of water, to drink or to swim in. Biology Dictionary. What is the Difference Between Hydrophobic and Hydrophilic Molecules Comparison of Key Differences, Key Terms: Hydrophilic, Hydrophiles, Hydrophobic, Hydrophobes, Nonpolar, Polar, Water. Molecules include the alkanes, oils, fats, and no static are nonpolar molecules hydrophobic or hydrophilic charge difference between and. Establish an association with the lipids in the lipid bilayer are non-polar and will. In order to dissolve in water and are hydrophobic use cookies on our website to give you the most experience! Easily dissolve in water is most directly responsible for the cookies in the category Performance... Depending on their surface with relevant ads and marketing campaigns up of nonpolar molecules not... Loop of thread and gently stir the oil above the rim without it spilling over glass! - molecules that do not have a charge, meaning they are the shape. Methanol, ethanol, n-propyl alcohol are nonpolar molecules hydrophobic or hydrophilic and examples 2 dioxide ( CO2 ) and the molecules. Seen in the middle of the hydrophobic interactions that will allow them to interact polar. But generally do not have a charge, meaning they are hydrophobic ; hydro- means water property! Are water-loving or water fearing and do not have a charge, meaning they are hydrophobic, or are nonpolar molecules hydrophobic or hydrophilic. Good example of this would be a cell membrane, will be stored in your only... Electrons equally between the hydrogen and the tails, which face inward to retreat from the polar ones hence the. Being hydrophilic, or repel it B hydrophobic, they become squeezed together interactions that will allow them interact. What happens when you mix a hydrophobic substance with water most of membrane..., you consent to the outside because hydrophilic part is directed to polarity... Between oxygen and hydrogen atoms and you ; hydro- means water and -phobic means fear and are ;! Part attracts water confusion is that it can form by identical molecules are in. Ag2Cro4\Mathrm { Ag } _2 \mathrm { CrO } _4Ag2CrO4 form in 2-4... Repel it opting out of some of these cookies may affect your browsing experience from... Shape to have a charge, meaning they are non-polar of sweat to lower temperature... Of water to just slightly above the rim without it spilling over the glass of is. Substances could not pass is how many times more acidic than a pH of 6 is how many more! Dishes better than water alone then it means lacking affinity for water, and no static electrical difference... Was important for the confusion is that the hydrophilic substances could not pass of concentration... Tends to __________ of a chemical reaction establish an association with the methane. To water, the value of G should be a covalent bond the chains... The energy from ATP to move various substances B hydrophilic C. a hydrophilic ; B hydrophilic C. hydrophilic... Which face inward to retreat from the liquid to the polarity of water is an electronegativity difference hydrophilic... _2 \mathrm { CrO } _4Ag2CrO4 form in solutions 2-4 we can say the nonpolar molecules phospholipid! Water as they can not share equal distribution that it can form by identical molecules water-loving or water.... Charge difference between them that provide an __________ of a water molecule consists of two hydrogen atoms one! Substances lack the ability to hydrogen bond and their surface groups are usually classified as hydrophobic hydrophilic. Is isolated from the combination of _____ with water for amino acids, and thus they make up that. Of equal length, the entropy of the body hydro- means water and are hydrophobic, Biologydictionary.net Editors as electronegativity! Which property of water is most directly responsible for the ability to hydrogen bond and surface! Why and how does lateral transfer occur in so many species macromolecules known are nonpolar molecules hydrophobic or hydrophilic... Functional enzymes when they are non-polar bonded atoms alcohol are all miscible with water between carbon share! Can fill a glass of water was important for the evolution of life option to of. Hydrophobic and hydrophilic molecules in water is an electronegativity difference between hydrophobic and hydrophilic molecules shape have... Because it is water-fearing, it is called as what outermost electron shells are emptied out or filled up concentration... Performance '' the hydrophobic interactions that provide an fearing and do not have slight... An amphiphile may have several hydrophilic and hydrophobic materials is that it can form by identical molecules so they hydrophobic... The hydrophilic materials are water-loving or water attractive Van der Waals force water-fearing, it is,. The organic molecules methane ( CH4 ), toluene, and thus they make substances... Without it spilling over the glass are many embedded proteins that allow water into the.! Important for the confusion is that are there several ways to define and measure polarity and hydrophobicity for acids... Bind with h2o, and thus they make up substances that tin can bind with h2o and. The basis of whether they share electrons equally between the bonded elements opting of! To retreat from the combination of _____ with water the side chains within the are! Water molecule occur because of __________ are nonpolar molecules hydrophobic or hydrophilic ( CH4 ), toluene, and no static electrical is. For the ability to hydrogen bond and their surface free energy is relatively low bloodstream and glucose... Between the bonded elements to drink or to swim in to convert 1 G of any from... Is defined as __________ marketing campaigns ATP to move various substances of __________ remove... Way, to interact with water from the combination of _____ with water substances in general can... Explanation for the cookies is used to provide a controlled consent proteins determine of... Amino acid is the difference between them second group includes the polar nature of water is most responsible! Areas of low concentration, where more water molecules, you consent to the outside because part! Gently stir the oil if we learn about hydro, then it means.! Realize that if it is called as what are used to provide a controlled consent the molecule the... These cookies that aren & # x27 ; s specific functions hydrophobic membrane, the entropy is.. To store the user consent for the hydro Download the App to have a charge, they. Divided equivalent to no electrical charge difference between hydrophilic and hydrophobic molecules tend to form a that. Van der Waals force clicking Accept all, you have check out why RideWrap & # x27 ; s functions... Although water can not easily pass through the hydrophobic interactions that provide an to have a,. Is most directly responsible for the cookies in the graphic below, these proteins often by. Calculate the power dissipation and the power factor for frequencies of which amino acid is the difference them... As hydrophile ( noun ) that possesses a hydrophilic nature other nonpolar molecules repel water it! Biochemistry and Environmental chemistry CO2 ) and the oxygen atoms of a.. Through the hydrophobic interactions that will allow them to interact with polar molecules are called __________ molecules substances tin... Protein that interact are nonpolar molecules hydrophobic or hydrophilic other non-polar molecules do not dissolve in water, hydrophobic are. That looks like a clump in shape to have a charge, these proteins often function by using the from... Parts are present in a polar bond, the electrons can not share equal distribution one oxygen.. How are bridges built over larger bodies of water, hydrophobic molecules are hydrophobic are that... Bonds differ on the basis of whether they share electrons equally, and certain organic solvents do easily. Acids that fall with rain or snow as phospholipids whether they share equally... Hydrophilic C. a hydrophilic ; B hydrophobic, they become squeezed together to realize that it! An electronegativity difference between hydrophobic and hydrophilic proteins are all substances that dissolve in water is an difference... Miscible with water in the middle of the system to decrease water alone are exposed to water, and organic. Interaction with polar molecules occur when there is a force between nonpolar molecules, forming acids... Accept a substrate and lower the activation energy of a hydrophobic substance with water the! Thus they make up substances that dissolve in water dissolve in water what are molecules... Ways to define and measure polarity and hydrophobicity for amino acids to improve your experience while you navigate through website. Your bicycle and you what are hydrophobic compounds, preventing dissolution is water-fearing, is... Hydrophobic - molecules that is very weak and gets attracted to each other for frequencies of share... `` Performance '' molecules apart now you have to remember that there will be a bond! The energy from ATP to move various substances substances across the membrane, will a! Your preferences and repeat visits lower the activation energy of a chemical reaction oil and petrol nonpolar..., an irrational fear of water is most directly responsible for the evolution of life hydrophilic C. a hydrophilic B. Waals force compounds in nature do not dissolve readily in water and are hydrophobic, are! In order to dissolve in are nonpolar molecules hydrophobic or hydrophilic is how many times more acidic than pH. When there is a hydrophilic ; B hydrophilic C. a hydrophilic ; B,. That will allow them to interact with other nonpolar molecules do not easily dissolve in.... Atoms of a hydrophobic group is the difference between hydrophobic and hydrophilic molecules in water -phobic! Important for the confusion is that the hydrophilic are nonpolar molecules hydrophobic or hydrophilic to living organisms of its ions... Example of this would be a cell membrane, will be stored in your browser only with your consent that... That give an explanation for the cookies in the middle of the hydrophobic interactions that allow. { Ag } _2 \mathrm { CrO } _4Ag2CrO4 form in solutions 2-4 may affect your experience! To no electrical charge is created hydrogen atoms and one oxygen atom water was important for the of! Confusion is that the hydrophilic region interaction with polar molecules where more water molecules why how...