CHAPTER 2 – CHEMISTRY
CHAPTER 2 – CHEMISTRY
1. MATTER
Anything that occupies space and has mass
- mass – quantity of matter an object has
- mass vs. weight
A. Elements
- pure substances that cannot be broken down chemically into simpler kinds of matter
- 90% of all living things contain C, H, O, N
- chemical symbols
Atoms
- simplest part of an element that retains all the properties of that element
1. nucleus – central core of atom with protons (+’ve charge) and neutrons (no charge)
- atomic number = # of protons
- atomic mass = # protons + # neutrons
2. electrons – travel in orbital outside of nucleus
– each orbital has a different energy level; farther away from nucleus, more energy
- first energy level holds a max of 2 electrons
- next few, 8
- how many e- in outer orbital determines an atom’s reactivity
Compounds
- elements do not usually exist by themselves
- compound = two or more different elements chemically bonded to each other
- chemical formula – tells how many atoms of what element (H2O)
- atoms are chemically stable when outermost energy level is filled
- atoms tend to combine with each other to achieve stability
- 2 kinds of bonds:
1. covalent
- atoms share one or more pairs of electrons
- polar covalent vs. nonpolar covalent
2. ionic
- electrons are transferred from one atom to another; the resulting oppositely charged ions are attracted to each other
2. ENERGY
A. Energy and Matter
- energy is the ability to do work or cause change
- free energy is the energy in a system that is available for work
- all atoms and molecules in a substance are in constant motion; rate of motion determines state (solid, liquid, gas)
B. Energy and Chemical Reactions
- reactants – left side of equation; products – right side
- chemical reactions that release energy = exergonic
- chemical reactions that require energy = endergonic
- both endergonic and exergonic chemical reactions require energy to start the reaction = activation energy
- catalysts = chemicals that speed up reactions by lowering activation energy; reaction will then proceed spontaneously or with little energy input
- enzymes = biological catalysts
- redox reactions = involve transfer of electrons
- oxidation reactions, atom loses one or more electrons; reduction reactions, atom gains one or more electrons
3. WATER AND SOLUTIONS
A. Polarity
- Water is polar – even though it is NOT a charged molecule, the distribution of charges across the molecule is uneven
- Water dissolves other polar substances (sugars, ionic compounds and some proteins)
- Spheres of hydration
B. Hydrogen Bonding
- Force of attraction between a hydrogen atom with a slight positive charge and another atom or molecule with a partial or full negative charge; water “clings” to itself and other polar substances
- Hydrogen bonding accounts for the unique properties of water
- Cohesion and adhesion
- Temperature moderation – water has a high heat capacity – it can absorb and release large amounts of heat with little temperature change
- This allows organisms to keep cells at relatively stable temperatures despite changes in environmental temperature
- High heat of vaporization – as liquid evaporates, the surface of the remaining liquid cools down – sweating
- Water is densest at 4oC
C. Describing solutions
- a mixture in which one or more substances are uniformly distributed in another substance
- no chemical alteration of either substance
- solute vs. solvent
- aqueous solutions (water is the solvent) are important to all living things
D. Acids and Bases
- breaking up of water molecule into two ions of opposite charge = dissociation
- H2O ( H+ + OH-
- OH- = hydroxide ion; H3O+ = hydronium ion
- Acids = # of hydronium ions > # hydroxide ions
- Bases = # hydroxide ions > # hydronium ions (alkaline substances)
- PH scale = measure of acidity or alkalinity (scale 0 – 14)
- In living things, to maintain homeostasis, pH must be controlled
- Buffers – chemicals which neutralize small amounts of acid or base added to a system
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