Chemistry of Life Chapter 2

Atom Element = the smallest unit of matter that cannot be broken down = a pure substance made of only one kind of atom

Atoms are composed of even smaller parts, called subatomic particles. Protons = positive electric charge (1+) Neutrons = neutral charge (0) Electrons = negative charge (1-)

Each element has a unique number of protons = atomic number.

Atoms have equal numbers of P and e- The atomic number = tells the number of protons and the number of electrons

Mass number = the sum of the number of protons and neutrons in the nucleus of an atom. # Neutrons = Mass # - Atomic # # protons? # electrons? # neutrons? Carbon =

YouTube - The element song

Atoms want to be “stable” = full valence shell. Chemical bonds Atoms want to be “stable” = full valence shell. Share or transfer electrons. To become stable, atoms will hold together by chemical bonds. The strongest chemical bonds are covalent bonds and ionic bonds.

Single Atoms Chemical Bond

A covalent bond is the sharing of a pair of electrons by two atoms. Hydrogen H2 Subscript (2 atoms)

Ionic bond = one atom strips an electron completely from the other. Ions = charged atoms or molecule NaCl

Top 4 Atoms found in Organisms? C = 18.5% H = 9.5% N = 3.3%

Properties of Water

Cells 70-95% Water ~75% Earth Astronomers Life evolved in water

H2O

- + Water is a “Polar Molecule” Polar Covalent Bond = electrons not shared equally - +

Hydrogen bonds = a weak chemical attraction between polar molecules. H+  O-

Cohesion = water molecules bonding to each other. “Surface tension” prevents stretch or break the surface

Adhesion = clinging of one substance to another (polar  polar).

Water is the “solvent” of life Solution = homogenous mixture. Solute = Solvent = substance dissolved dissolving agent

Forms hydrogen bonds with charged and polar covalent molecules. Solvent? Solute? “Dissolve”

pH

0 - 14 7 = neutral (H+ = OH-) 0-6 = acidic (H+) 8-14 = basic (OH-) pH scale = concentration of H+ in a solution 0 - 14 7 = neutral (H+ = OH-) 0-6 = acidic (H+) 8-14 = basic (OH-)

Acid = any compound that forms hydrogen ions (H+) ions in solution Base = any compound that forms hydroxide ions (OH-) in solution Factor of 10

Buffers = weak acids or Cell pH = 6.5 – 7.5 “Homeostasis” bases that prevent sudden changes in pH