Copyright 2005 Pearson Education Inc publishing as Benjamin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Atom- Molecule-Element- Compound Relationship Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chemical Building Blocks Of Life • A few other elements – Make up the remaining 4% of living matter Table 2. 1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Dissecting An Atom Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energy Levels Of Electrons • Energy levels – Are represented by electron shells Third energy level (shell) Second energy level (shell) Energy absorbed First energy level (shell) Energy lost Atomic nucleus Figure 2. 7 B (b) An electron can move from one level to another only if the energy it gains or loses is exactly equal to the difference in energy between the two levels. Arrows indicate some of the step-wise changes in potential energy that are possible. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Periodic Table • The periodic table of the elements – Shows the electron distribution for all the elements Hydrogen 1 H Atomic mass First shell Lithium 3 Li Beryllium 4 Be Boron 3 B Carbon 6 C 2 He 4. 00 Nitrogen 7 N Atomic number Helium 2 He Element symbol Electron-shell diagram Oxygen Fluorine 8 O 9 F Neon 10 Ne Second shell Sodium Magnesium Aluminum Silicon Phosphorus Sulfur 13 Al 16 S 11 Na 12 Mg 14 Si 15 P Third shell Figure 2. 8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chlorine 17 Cl Argon 18 Ar
Electron Shells and Orbital • Each electron shell – Consists of a specific number of orbitals Electron orbitals. Each orbital holds up to two electrons. x Y Z 1 s orbital 2 s orbital Three 2 p orbitals 1 s, 2 s, and 2 p orbitals Electron-shell diagrams. Each shell is shown with its maximum number of electrons, grouped in pairs. Figure 2. 9 (a) First shell (maximum 2 electrons) (b) Second shell (maximum 8 electrons) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (c) Neon, with two filled shells (10 electrons)
Covalent Bond • Formation of a covalent bond Hydrogen atoms (2 H) 1 2 3 In each hydrogen atom, the single electron is held in its orbital by its attraction to the proton in the nucleus. When two hydrogen atoms approach each other, the electron of each atom is also attracted to the proton in the other nucleus. The two electrons become shared in a covalent bond, forming an H 2 molecule. Figure 2. 10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings + + + Hydrogen molecule (H 2)
• Single and double covalent bonds Name (molecular formula) Electronshell diagram Structural formula (a) Hydrogen (H 2). Two hydrogen atoms can form a single bond. H H O O (b) Oxygen (O 2). Two oxygen atoms share two pairs of electrons to form a double bond. Figure 2. 11 A, B Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Spacefilling model
• Covalent bonding in compounds Name (molecular formula) Electronshell diagram (c) Water (H 2 O). Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. (d) Methane (CH 4). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. Structural formula O H H C H Figure 2. 11 C, D Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H Spacefilling model
Polarity & Electro negativity • In a polar covalent bond – The atoms have differing electronegativities – Share the electrons unequally Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. – This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. O Figure 2. 12 + H H H 2 O Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings +
Ionic Bond • An ionic bond – Is an attraction between anions and cations The lone valence electron of a sodium atom is transferred to join the 7 valence electrons of a chlorine atom. 1 2 Each resulting ion has a completed valence shell. An ionic bond can form between the oppositely charged ions. + Na Na Figure 2. 13 Sodium atom (an uncharged atom) Cl Cl Chlorine atom (an uncharged atom) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Na Na+ Sodium on (a cation) – Cl Cl– Chloride ion (an anion) Sodium chloride (Na. Cl)
Hydrogen Bonds • A hydrogen bond – Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom – Water (H 2 O) + H O H + – Ammonia (NH 3) N H + Figure 2. 15 H H + Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings + A hydrogen bond results from the attraction between the partial positive charge on the hydrogen atom of water and the partial negative charge on the nitrogen atom of ammonia.
Van der Waals Interactions • Van der Waals interactions – Occur when transiently positive and negative regions of molecules attract each other Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Structure Of A Molecule • In a covalent bond – The s and p orbitals may hybridize, creating specific molecular shapes Three p orbitals Z s orbital Four hybrid orbitals X Y Tetrahedron (a) Hybridization of orbitals. The single s and three p orbitals of a valence shell involved in covalent bonding combine to form four teardrop-shaped hybrid orbitals. These orbitals extend to the four corners of an imaginary tetrahedron Figure 2. 16 (a) (outlined in pink). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ball-and-stick model Space-filling model Hybrid-orbital model (with ball-and-stick model superimposed) Unbonded Electron pair O O H Water (H 2 O) 104. 5° H H C C H H Methane (CH 4) H H H (b) Molecular shape models. Three models representing molecular shape are shown for two examples; water and methane. The positions of the hybrid orbital determine the Figure 2. 16 (b) shapes of the molecules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Structural Similarities Carbon Nitrogen Hydrogen Sulfur Oxygen Natural endorphin Morphine (a) Structures of endorphin and morphine. The boxed portion of the endorphin molecule (left) binds to receptor molecules on target cells in the brain. The boxed portion of the morphine molecule is a close match. Natural endorphin Brain cell Figure 2. 17 Morphine Endorphin receptors (b) Binding to endorphin receptors. Endorphin receptors on the surface of a brain cell recognize and can bind to both endorphin and morphine. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chemical Reactions • Chemical reactions – Convert reactants to products + 2 H 2 Reactants + O 2 Reaction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 H 2 O Product
- Slides: 18