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 10-24 grams. Employing this value, the masses of the fundamental particles of an atom have been determined to be:

• (1) Proton mass: 1.00727 amu. • (2) Neutron mass: 1.00867 amu. • (3) Electron mass: 0.00055 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 = 1.00794 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

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