Reading the Table of Elements

Unit 2: The Characteristics of Life and Cells Section 1a: Water

Water is the most flexible and essential substance in the world, especially for living things. It covers about 75% of the earth’s surface and makes up about 75% of your body composition. It can easily be made into a solid, liquid, or gas. Its molecular structure is extremely stable, allowing water to be predictable.

Molecule- smallest unit of most compounds that displays all the properties of that compound.

Some properties of water:

 Found as a liquid at normal temperatures and in most locations.  Expands when it freezes. (Most substances shrink)  Ice (solid state) floats, an unusual quality.  Molecule is shaped like a V

Forms of Attraction Water molecules are neutral, meaning they are not charged overall. However, water molecules are like tiny magnets. A water molecule is polar, which means it has a more positive side and a more negative side. What causes this? There is an uneven distribution of electrons between the oxygen and hydrogen atoms.

Unit 2, Section 1a, Page 1 Label the positive and negative ends. Water molecules are attracted to one another more than other substances. The bonds that attract water molecules to other molecules are called hydrogen bonds. These kinds of bonds are not as strong as ionic or covalent bonds but they are the strongest bond that can form between molecules. A single water molecule can engage in up to 4 hydrogen bonds.

Cohesion- Attraction between molecules of the same substance.

Adhesion- Attraction between molecules of different substances.

So cohesion is when water molecules are attracted to one another and adhesion is when water molecules are attracted to something else like the windshield of a car or the inside of a straw. Cohesion also causes water molecules to pull inward on the surface into a small dome-like shaped. So when you see beads of water, they look like half circles. Adhesion was why there was a curve in the water in the graduated cylinder we measured. The water was sticking to the sides of the instrument.

Surface Tension: a property that allows the surface of a liquid to act like elastic because of cohesion.

Capillary Action- the rise of water through a narrow tube against gravity.

Example: Plants use thin tubes to move water from the roots up to the leaves.

Solutions and Suspensions

Mixture- a material composed of two or more elements or compounds that are physically mixed together but not chemically combined.

Solution- a mixture of two or more substances in which the molecules of the substances are evenly mixed.

Unit 2, Section 1a, Page 2 Solutions have two parts, the solutes and the solvents. The solvent is the substance that is dissolving the solute. The greatest solvent in the world is also one of the most common… yes, it’s water.

Salt Water Solvent Solute

Suspension- a mixture of water and nondissolved substances that are so small they do not settle out.

Acids, Bases, and pH

Ion- a charged atom that is either positive or negative.

Water is neutral but when one of the covalent bonds is broken, the two resulting atoms (Oxygen and Hydrogen) become ions, or charged atoms. However, the overall liquid is still neutral because there are just as many negatives as positives. (Refer to the next page)

~Neutral substances have equal amounts of hydroxide ions and hydrogen ions. pH- a measurement of hydroxide ions. (H+)

For every whole number that you go left or right on the pH scale, the amount of ions goes up by a multiple of 10.

Unit 2, Section 1a, Page 3 Base- substances that have more hydroxide ions. (OH-)

Acid- substances that have more hydrogen ions. (H+)

Unit 2, Section 1a, Page 4