Why is water molecules polar

Be sure students realize that no protons or electrons are gained or lost. The water molecule has a total of 10 protons and 10 electrons 8 from the oxygen atom and 1 from each of the two hydrogen atoms. Since it has the same number of protons and electrons, the water molecule is neutral. Tell students that another way to see the difference in where the electrons are is by using the electron cloud model.

Unequal sharing of electrons makes water a polar molecule. Tell students that the oxygen atom attracts electrons a little more strongly than hydrogen does. So even though the electrons from each atom are attracted by both the oxygen and the hydrogen, the electrons are a bit more attracted to the oxygen. This means that electrons spend a bit more time at the oxygen end of the molecule.

This makes the oxygen end of the molecule slightly negative. Since the electrons are not near the hydrogen end as much, that end is slightly positive.

When a covalently bonded molecule has more electrons in one area than another, it is called a polar molecule. The electron cloud model can show an unequal sharing of electrons. Point out that the electron cloud around the oxygen is darker than the electron cloud around the hydrogen. This shows that electrons are more attracted to the oxygen end of the molecule than the hydrogen end, making the water molecule polar.

Tell students that this is another model of a water molecule. In this model, color is used to show the polar areas of the water molecule. The negative area near the oxygen atom is red, and the positive area near the hydrogen atoms is blue. Ask students: What do you notice about the way water molecules orient themselves?

The red oxygen area of one water molecule is near the blue hydrogen end of another water molecule. Why do water molecules attract one another like this? Since the oxygen end of a water molecule is slightly negative and the hydrogen end is slightly positive, it makes sense that water molecules attract one another.

Give each student an activity sheet. Show students that the bonds between atoms in a molecule are different from the polar attractions between molecules. The bonds within molecules and the polar attractions between molecules. A single atom stays together because of the attraction between the positively charged protons and the negatively charged electrons.

In a molecule, two or more atoms stay together because of the mutual attraction between the positively charged protons from one atom and the negatively charged electrons from the other atom. This causes the covalent or ionic bonding that holds atoms or ions together. Two or more water molecules stay together because of the positive and negative parts of the molecules attracting each other. Have students mark the positive and negative areas on a water molecule by color-coding their Styrofoam ball models.

Repeat this for your other water molecule. Position your water molecules so that opposite charges are near each other. Ask students: How do your Styrofoam ball models of water molecules relate to the color-coded charge density model shown in the animation?

The different colors show that water is a polar molecule. Because water molecules are polar, how do they arrange themselves in liquid water? The positive area of one water molecule is attracted to the negative area of another water molecule. Explore Have students design a test to compare the rate of evaporation between water and alcohol. Ask students: Do you think a substance like water with polar molecules would evaporate faster or slower than a substance like alcohol with molecules that are not as polar?

The more-polar molecules will stick together more and will probably evaporate more slowly than less polar molecules. Less-polar molecules should evaporate faster because they are not as attracted to each other. How could you design a quick and easy evaporation test to compare the rate of evaporation between water and alcohol?

What materials will you need? Should you use the same amount of water and alcohol? Here's how it works for water. Water H 2 O is polar because of the bent shape of the molecule. The shape means most of the negative charge from the oxygen on side of the molecule and the positive charge of the hydrogen atoms is on the other side of the molecule. This is an example of polar covalent chemical bonding. When solutes are added to water, they may be affected by the charge distribution.

The reason the shape of the molecule isn't linear and nonpolar e. The electronegativity value of hydrogen is 2. The smaller the difference between electronegativity values, the more likely atoms will form a covalent bond.

A large difference between electronegativity values is seen with ionic bonds. Hydrogen and oxygen are both acting as nonmetals under ordinary conditions, but oxygen is quite a bit more electronegative than hydrogen, so the two atoms form a covalent chemical bond, but it's polar. The highly electronegative oxygen atom attracts electrons or negative charge to it, making the region around the oxygen more negative than the areas around the two hydrogen atoms.

The electrically positive portions of the molecule the hydrogen atoms are flexed away from the two filled orbitals of the oxygen. Basically, both hydrogen atoms are attracted to the same side of the oxygen atom, but they are as far apart from each other as they can be because the hydrogen atoms both carry a positive charge. The bent conformation is a balance between attraction and repulsion. Remember that even though the covalent bond between each hydrogen and oxygen in water is polar, a water molecule is an electrically neutral molecule overall.

Each water molecule has 10 protons and 10 electrons, for a net charge of 0. The shape of each water molecule influences the way it interacts with other water molecules and with other substances. Water acts as a polar solvent because it can be attracted to either the positive or negative electrical charge on a solute. The slight negative charge near the oxygen atom attracts nearby hydrogen atoms from water or positive-charged regions of other molecules.

The slightly positive hydrogen side of each water molecule attracts other oxygen atoms and negatively-charged regions of other molecules. When molecules are symmetrical , however, the atoms pull equally on the electrons and the charge distribution is uniform. Symmetrical molecules are nonpolar.

Because nonpolar molecules share their charges evenly, they do not react to electrostatic charges like water does. Covalent molecules made of only one type of atom, like hydrogen gas H2 , are nonpolar because the hydrogen atoms share their electrons equally.

Molecules made of more than one type of covalently bonded nonmetal atoms, like carbon dioxide gas CO2 , remain nonpolar if they are symmetrical or if their atoms have relatively equal pull. Even large compounds like hexane gasoline C6H14 , is symmetrical and nonpolar. Electrostatic charges do not seem to have much, if any, effect on nonpolar compounds. Further Investigations. Activity: Water and Electrostatic Forces. Special Features:. Representative Image:.

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