6. Figure 2.8
(a) A ball bouncing down a flight
of stairs provides an analogy
for energy levels of electrons.
Third shell (highest energy
level in this model)
Second shell (higher Energy
energy level) absorbed
First shell (lowest energy
level)
Energy
lost
Atomic
nucleus
(b)
7. Figure 2.9
Hydrogen 2 Atomic number Helium
1H He 2He
Mass number 4.00 Element symbol
First
shell Electron
distribution
diagram
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
3Li 4Be 5B 6C 7N 8O 9F 10Ne
Second
shell
Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon
11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar
Third
shell
45. Experimental Controls
Isolation of variables
• Negative Control • Positive Control
– Guards against false – Guards against false
positives. negatives.
– ensure that there is no – ensure that there is an
effect when effect when there
there should be no should be an effect
effect
Notas del editor
Figure 1.3 Some properties of life.
Figure 1.4 Exploring: Levels of Biological Organization
Table 2.1 Elements in the Human Body
Figure 2.5 Simplified models of a helium (He) atom.
Figure 2.8 Energy levels of an atom’s electrons.
Figure 2.9 Electron distribution diagrams for the first 18 elements in the periodic table.
Figure 2.16 A hydrogen bond.
Figure 2.14 Electron transfer and ionic bonding.
Figure 2.18 A molecular mimic.
Figure 2.UN02
Figure 2.19 Photosynthesis: a solar-powered rearrangement of matter.
Figure 3.10 The pH scale and pH values of some aqueous solutions.
