Sodium Chlorine Sodium chloride 1

ReactantsReactionProducts 2 H 2 2 H 2 OO2O2 + 2

3

Nucleus Protons (+ charge) determine element Neutrons (no charge) determine isotope Electrons (– charge) form negative cloud and determine chemical behavior Atom 4

Cloud of negative charge (2 electrons) Electrons Nucleus (a)(b) 5

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 level) First shell (lowest energy level) Atomic nucleus Energy absorbed Energy lost (b) (a) 6

Electron orbitals 7

Neon, with two filled Shells (10 electrons) First shell Second shell First shellSecond shell 1s orbital2s orbitalThree 2p orbitals (a) Electron distribution diagram (b) Separate electron orbitals (c) Superimposed electron orbitals 1s, 2s, and 2p orbitals x y z 8

First shell Second shell Third shell Hydrogen 1 H Lithium 3 Li Sodium 11 Na Beryllium 4 Be Magnesium 12 Mg Boron 5 B Aluminum 13 Al Carbon 6 C Silicon 14 Si Nitrogen 7 N Phosphorus 15 P Oxygen 8 O Sulfur 16 S Fluorine 9 F Chlorine 17 Cl Neon 10 Ne Argon 18 Ar Helium 2 He 2 He 4.00 Mass number Atomic number Element symbol Electron distribution diagram 9

+ – Na Sodium atom Cl Chlorine atom Na + Sodium ion (a cation) Cl – Chloride ion (an anion) Ionic bond Electronic transfer forms ions 10

Na + Cl – 11

Hydrogen atoms (2 H) Hydrogen molecule (H 2 ) 12

Single covalent bond Double covalent bond 13

(a) Hydrogen (H 2 ) (b) Oxygen (O 2 ) (c) Water (H 2 O) Name and Molecular Formula Electron Distribution Diagram Lewis Dot Structure and Structural Formula Space- Filling Model (d) Methane (CH 4 ) 14

H H H2OH2O ++ ++ –– O 15

Water (H 2 O) Ammonia (NH 3 ) Hydrogen bond –– –– ++ ++ ++ ++ ++ 16

s orbital Three p orbitals Four hybrid orbitals Tetrahedron (a) Hybridization of orbitals z x y Space-Filling Model Ball-and-Stick Model Hybrid-Orbital Model (with ball-and-stick model superimposed) Unbonded Electron pair Water (H 2 O) Methane (CH 4 ) (b) Molecular-shape models 17

Natural endorphin Morphine Carbon Hydrogen Nitrogen Sulfur Oxygen (a) Structures of endorphin and morphine (b) Binding to endorphin receptors Brain cell Morphine Natural endorphin Endorphin receptors 18