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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