9 2.5 Absolutely Necessary Chemistry Summary
Lisa Bartee; Walter Shriner; and Catherine Creech
What exactly do you need to know?
Matter
- Matter is anything that occupies space and has mass.
- Matter is made up of atoms of different elements.
- All of the 92 elements that occur naturally have unique qualities that allow them to combine in various ways to create compounds or molecules.
- Atoms consist of protons, neutrons, and electrons.
- Atoms are the smallest units of an element that retain all of the properties of that element.
Chemical Bonds
- Electrons can be donated or shared between atoms to create bonds.
- Ionic bonds form between a positively and a negatively charged atom. They are fairly strong bonds.
- Covalent bonds form when atoms share one or more electrons. They are very strong bonds.
- Hydrogen bonds form between partially charged atoms. They are weak bonds.
- van der Waals interactions form between polar, covalently bound atoms. They are weak attractions that are often temporary.
Water
- is POLAR, allowing for the formation of hydrogen bonds,
- is an excellent SOLVENT: because water is polar, it allows ions and other polar molecules to dissolve.
- STABILIZES TEMPERATURE: the hydrogen bonds between water molecules give water the ability to hold heat better than many other substances. As the temperature rises, the hydrogen bonds between water continually break and reform, allowing for the overall temperature to remain stable, although increased energy is added to the system.
- is COHESIVE: hydrogen bonds allow for the property of surface tension.
pH, Acids, Bases, and Buffers
- The pH of a solution is a measure of the concentration of hydrogen ions in the solution. The pH scale ranges from 0 to 14.
- A solution with an equal number of hydrogen ions and hydroxide ions is neutral and has a pH of 7.
- A solution with a high number of hydrogen ions is acidic and has a low pH value (below 7).
- A solution with a high number of hydroxide ions is basic and has a high pH value (above 7).
- Buffers are solutions that moderate pH changes when an acid or base is added to the buffer system. Buffers are important in biological systems because of their ability to maintain constant pH conditions.