Chemical Bonds, Water, Solutions-Week 1

A covalent bond between two element with the same/ nearly the same electronegativity and electrons are shared equally. Example: H-H, O=O, C-H

Nonpolar covalent bond

The hydrogen atoms of one molecule, with their partial positive charges, would repel the hydrogen atoms of the adjacent molecule.

Why is it unlikely for water molecules to bond between their hydrogen regions?

Ionic bonds are being broken between Na+ and Cl- and each atom is forming hydrogen bonds.

When salt crystals dissolve in water, what types of bonds are being broken and forming?

Each carbon atom has only three covalent bonds instead of the required four.

Why does the structure H-C=C-H fail to make sense chemically?

The hydrophobic substance repels water, perhaps helping to keep the ends of the legs from becoming coated with water and breaking through the substance. If the legs were coated with a hydrophilic substance, water would be drawn up them, possibly making it more difficult for the water strider to walk on water.

A water strider (which can walk on water) has legs that are coated with a hydrophobic substance. What might be the benefit? What would happen if the substance were hydrophilic?

Hydrogen bonds hold neighboring water molecules together. this cohesion helps chains of water molecules move upward against gravity in water-conducting cells aw water evaporates from the leaves. Adhesion between water molecules and the walls of the water-conducting cells also helps counter gravity.

Describe how properties of water contribute to the upward movement of water in a tree.

Covalent bonds allow these two atoms to bond. They share valence electrons in order to fill their outermost shell and creating a more stable molecule.

Explain how carbon and hydrogen atoms can share electrons to achieve stable, full outer electron shells in both.

High humidity hampers cooling by suppressing the evaporation of sweat.

Explain the saying, "It's not the heat; it's the humidity".

Oil separating from water into globules.

Give an example of a hydrophobic interaction.

This is the bond between water molecules.

Give an example of a substance that forms a hydrogen bond.

As water freezes, it expands because water molecules move farther apart in forming ice crystals. When there is water in a crevice of a boulder, the expansion due to freezing may crack the boulder.

How can the freezing of water crack boulders?

Water's high specific heat helps regulate temperatures on earth. Its adhesive properties allow for water to flow up the roots of plants which allows for plants to grow and be eaten by other organisms. Water's solubility is perfect for absorption of nutrient and their transport throughout the body through blood which is composed mostly of water.

How do the properties of water make it an ideal medium for life on earth?

hydrogen bond - a weak inter-molecular attraction between an atom (often O or N) carrying a partial negative charge and a hydrogen carrying a partial positive charge. The tendency of nonpolar molecules in a polar solvent (usually water) to interact with one another is called the hydrophobic effect. The interactions between the nonpolar molecules are called hydrophobic interactions.

Hydrogen bonding and hydrophobic interactions are both very weak bonds. How do they differ from each other?

If you could synthesize molecules that mimic these shapes, you might be able to treat diseases or conditions caused by the inability of affected individuals to synthesize such molecules. Example: morphine mimicking the shape of endorphins and triggering endorphin receptors, thus causing euphoria and pain relief.

If you were a pharmaceutical researcher why would you want to learn the three-dimensional shapes of naturally occurring signaling molecules?

1) Water has a high specific heat due to hydrogen bonding which is a result of water molecules being very polar. It requires more heat to break apart the hydrogen bonds between water molecules. 2)High surface tension of water is a result of hydrogen bonds. 3)Its ability to be used as a solvent for ionic molecules (salt) and nonionic polar molecules (sugar).

Name at least 3 properties of water that emerge from its highly polar molecular structure.

A covalent bond between two elements with different electronegativity in which shared electrons are more attracted to on element of the molecule than the other.

Polar covalent bond

1)O-H 2)N-H 3)C-H 4)O-O

Rank these covalent bond types from most polar to least polar: N-H, O-O, C-H, O-H

Four

Up to how many hydrogen atoms can covalently bond to one carbon atom?

The residual attractive or repulsive forces between molecules or atomic groups that do not arise from a covalent bond, or ionic bonds. Molecules with nonpolar covalent bonds have positively and negatively charged regions. The Electrons are not evenly distributed; at any instant, they may accumulate by chance in one part of a molecule or another. The results are ever-changing regions of positive and negative charge that enable all atoms and molecules to stick to one another. These attractions are weak and only occur when atoms and molecules are very close to one another. When many such interactions occur simultaneously however, they become quite powerful.

Van der Waals forces

The attraction between oppositely charged ions, forming ionic bonds.

What holds the atoms together in a crystal of magnesium chloride (MgCl2)?

Lipid bilayer

What hydrophobic formation of molecules created the formation of this membrane?

A liquid which has a high concentration of OH- ions and low concentration of H+ ions. On the pH scale it is greater than 7. An example is bleach.

What is a base? Give an example.

When hydrogen is covalently bonded to an electronegative atom, the hydrogen atom has a partial positive charge that allows it to be attracted to a different electronegative atom nearby. In living cells, the electronegative partners are usually oxygen or nitrogen atoms.

What is a hydrogen bond?

A liquid which has a high concentration of H+ ions and low concentrations of OH- ions. On the pH scale it is any substance that is less than 7. An example is lemon juice.

What is an acid? Give an example.

Electronegativity is the attraction of an atom for the electrons of a covalent bond. Because oxygen is more electronegative than hydrogen, the oxygen atom in H2oO pulls electrons toward itself, resulting in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. Atoms in neighboring water molecules with opposite partial charges are attracted to each other, forming a hydrogen bond.

What is electronegativity, and how does it affect interactions between water molecules?

the number of moles of solute per liter of solution.

What is the definition of molarity?

Micelle

What is this formation of hydrophobic molecules called?

A molecule which has positive and negative regions that can form hydrogen bonds with water. An example would be table salt (NaCl) which has positive sodium atoms and negatively charged chlorine atoms. The negatively charged hydrogen region of water molecules are attracted to the sodium and the positively charged oxygen region of water molecules are attracted to the chlorine. These attractions form hydrogen bonds which cause the water molecules to separate the Na+ and Cl- atoms, surrounding the each type of atom in hydration shells and leads to the water dissolving the table salt and creating a solution of two solutes, sodium cations and chloride anions.

What makes a molecule hydrophilic? Give an example

Molecules which are nonionic and nonpolar ( or otherwise unable to form hydrogen bonds) repel water. An example is vegetable oil, which has a prevalence of relatively nonpolar covalent bonds, in this case bonds between carbon and hydrogen, which share electrons almost equally. Therefore there is no attraction with water molecules.

What makes a molecule hydrophobic? Give an example.

The covalent bonds of water molecules would not be polar, and water molecules would not form hydrogen bonds with each other.

What would be the effect on the properties of the water molecule if oxygen and hydrogen had equal electronegativity?