Biology Chapter 2

Matter Anything that has mass and volume Elements = simplest stable form of matter Made of atoms Compounds = chemically combined elements Made of molecules

atom:element::molecule:compound Remember this

98% of crust is 8 elements and their compounds

Atomic Structure Small electrons in cloud (- charge) Much larger protons in nucleus (+ charge) Slightly larger neutrons in nucleus (0 charge) Every element unique

Common units of mass, such as grams, are much too large to conveniently describe the mass of an atomic nucleus or any of its constituent parts. To solve this problem a new unit was defined: the atomic mass unit (amu). The atomic mass unit is a relative unit defined arbitrarily by assigning a mass of 12 amu to the neutral atom carbon-12, the common isotope of carbon. One atomic mass unit equals 1.66 X grams. Employing this value, the masses of the fundamental particles of an atom have been determined to be: (1) Proton mass: amu. (2) Neutron mass: amu. (3) Electron mass: amu.

= atomic number

= atomic mass

Forms of the same element Differ in # of neutrons Same atomic number but different atomic mass (heavier) Similar behavior with some different properties Leads to average atomic mass H = amu

Ions

Valence electrons create behaviors/properties and establish periodic groups on table

Metals have 1-3 valence electrons and lose them easily Non-metals have 4-7 electrons and tend to gather more

Mendeleev’s Table

2 and 8 electrons create unreactive state (Happy) Is this important?

How do they become “happy”? Chemical bonding!

Ionic bond – giving/taking e-

Covalent bond – sharing e-

Polar covalent molecule + _

Van der Waal’s Forces Dispersion interaction –Between any molecule with unbalanced charges Dipole-dipole attraction –Between polar molecules like water

Mixtures Unlike a compound, the components are not chemically combined, just physically combined Heterogenous – not equally mixed Homogenous – “solution” and equally mixed (dissolved) Suspension – equally mixed small components and suspended Colloid - equally mixed larger components and suspended

Colloids can be classified as follows: Left: Fine sand (silica) added to water will quickly settle, producing a heterogeneous mixture with water on top and silica on the bottom. Right: The same proportion of silica, specially prepared, produces something different. The particles of hydrated silica are much larger than atoms and ordinary molecules. The similarly charged silica particles repel one another and stay suspended indefinitely, which is a colloid.

Buffers Dissolved compounds Weak acid or base React with strong acids and bases to prevent sharp, sudden changes in pH