1. Fundamental Building Blocks: Chemistry, Water, and pH

2. 2.1 Chemistry’s Building Block: The Atom

3. Chemistry’s Building Block: The Atom
The fundamental unit of matter is the atom.

4. Protons, Neurons, and Electrons
The three most important constituent parts of an atom are
protons
neutrons
electrons

5. Protons, Neurons, and Electrons
Protons and neutrons exist in the atom’s nucleus, while electrons move around the nucleus, at some distance from it.

6. Chapter 2 Lecture electron (negative charge) electron shell proton
(positive charge)
nucleus
neutron
(no charge)
Hydrogen (H)
Helium (He)
Figure 2.2

7. Protons, Neurons, and Electrons
Protons are positively charged.
Electrons are negatively charged.
Neutrons carry no charge.

8. The Element
An element is any substance that cannot be reduced to any simpler set of constituent substances through chemical means.
Each element is defined by the number of protons in its nucleus.

9. The Element
The number of neutrons in an atom can vary independently of the number of protons.
Thus, a single element can exist in various forms, called isotopes, depending on the number of neutrons it possesses.

10. The Element Hydrogen Deuterium Tritium 1 proton 0 neutrons 1 proton
Figure 2.5

11. The Element PLAY PLAY PLAY
Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 1: Animation
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Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 2: Exercise 1
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Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 3: Exercise 2

12. The Element Protons are positively charged.
Electrons are negatively charged.
Neutrons carry no charge.

13. 2.2 Matter is Transformed Through Chemical Bonding

14. Matter is Transformed Through Chemical Bonding
Atoms can link to one another in the process of chemical bonding.

15. Covalent Bond Covalent bond: atoms share one or more electrons
Ionic bond: atoms lose and accept electrons from each other

16. Covalent Bond
Chemical bonding comes about as atoms “seek” their lowest energy state.
An atom achieves this state when it has a filled outer electron shell.

17. Covalent Bond
Hydrogen and helium require two electrons in orbit around their nuclei to have filled outer shells.
Most other elements require eight electrons to have filled outer shells.

18. Covalent Bond Figure 2.7 Unstable, very reactive atoms
Stable, unreactive atoms
hydrogen (H)
helium (He)
carbon (C)
neon (Ne)
sodium (Na)
argon (Ar)
Outermost electron
shells unfilled
Outermost electron
shells filled
Figure 2.7

19. Covalent Bond
A molecule is a compound of a defined number of atoms in a defined spatial relationship.
For example, two hydrogen atoms can link with one oxygen atom to form one water molecule.

20. Covalent Bond (a) Two hydrogen atoms and one oxygen atom
hydrogen (H)
atom
hydrogen (H)
atom
hydrogen (H)
atom
hydrogen (H)
atom
oxygen (O)
atom
oxygen (O)
atom
(a) Two hydrogen atoms and one oxygen atom
(b) One water molecule
Figure 2.8

21. Covalent Bond
Atoms of different elements differ in their power to attract electrons.
The term for measuring this power is electronegativity.

22. Polar and Nonpolar Bonding
Through electronegativity, a molecule can take on a polarity—a difference in electrical charge at one end compared to the other.

23. Polar and Nonpolar Bonding
Covalent chemical bonds can be polar or nonpolar.
A polar covalent bond exists when shared electrons are not shared equally among atoms in a molecule, due to electronegativity differences.

24. Polar and Nonpolar Bonding
(a) Polar water molecule
(b) Nonpolar methane molecule
slight
negative
charge
polar
nonpolar
because
charges are
symmetric
slight
positive
charge
Figure 2.9

25. Ionic Bonding
Two atoms will undergo a process of ionization when the electronegativity differences between them are great enough that one atom loses one or more electrons to the other.
This process creates ions: atoms whose number of electrons differs from their number of protons.

26. Ionic Bonding
The charge differences that result from ionization can produce an electrostatic attraction between ions.
This attraction is an ionic bond.
When atoms of two or more elements bond together ionically, the result is an ionic compound.

27. Ionic Bonding Figure 2.10 sodium atom (Na) chlorine atom (Cl)
(a) Initial instability
Sodium has but
a single electron
in its outer shell,
while chlorine
has seven, meaning
it lacks only a single
electron to have a
completed outer
shell.
electron
transfer
(b) Electron transfer
When these two
atoms come
together, sodium
loses its third-shell
electron to chlorine,
in the process
becoming a sodium
ion with a net
positive charge
(because it now has
more protons than
electrons). Having
gained an electron,
the chlorine atom
becomes a chloride
ion, with a net
negative charge
(because it has
more electrons
than protons).
chloride ion
(Cl–)
sodium ion (Na+)
ionic
compound
(Na+Cl–)
(c) Ionic attraction
The sodium and chloride
ions are now attracted to
each other because they
are oppositely charged.
(d) Compound formation
The result of this electrostatic
attraction, involving many
sodium and chloride ions, is a
sodium chloride crystal (NaCl),
better known as table salt.
salt crystals
Figure 2.10

28. Hydrogen Bonding
Hydrogen bonding links an already covalently bonded hydrogen atom with an electronegative atom.

29. Hydrogen Bonding
In water, a hydrogen atom of one water molecule will form a hydrogen bond with an unshared oxygen electron of a neighboring water molecule.

30. Hydrogen Bonding
hydrogen bond
Figure 2.11

31. Hydrogen Bonding
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Animation 2.2: Chemical Bonding

32. 2.3 Some Qualities of Chemical Compounds

33. Some Qualities of Chemical Compounds
The three-dimensional molecular shape is important in biology because it determines the capacity molecules have to bind with one another.

34. Molecular Shape good fit, scent is smelled signal to brain
signal molecules
(aroma from bread)
receptor
molecules
bad fit,
scent is not
smelled
cells of nasal
passage
Figure 2.13

35. Molecular Shape
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Animation 2.3: Geometry, Chemistry, and Biology

36. 2.4 Water and Life

37. Water and Life
Water has several qualities that have strongly affected life on Earth.

38. Water is a Major Player in Many of Life’s Processes
A solution is a homogeneous mixture of two or more kinds of molecules, atoms, or ions.
The compound dissolved in solution is the solute; the compound doing the dissolving is the solvent.

39. Water is a Major Player in Many of Life’s Processes
(a) Attraction
(b) Separation
(c) Dispersion
water (solvent)
Sodium and chloride ions dissolved in water H O H
Na+
Cl–
sodium chloride (solute)
Sodium chloride’s positively charged sodium ions (Na+) are attracted to water’s negatively charged oxygen atoms, while its negatively charged chloride ions (Cl–) are attracted to water’s positively charged hydrogen atoms.
Pulled from the crystal, and separated from each other by this attraction, sodium and chloride ions become surrounded by water molecules.
This process of separating sodium and chloride ions repeats until both ions are evenly dispersed, making this an aqueous solution.
Figure 2.15

40. Water is a Major Player in Many of Life’s Processes
Water is a powerful solvent, with the ability to dissolve more compounds in greater amounts than any other liquid.

41. Water’s Structure Gives It Many Unusual Properties
Because water’s solid form (ice) is less dense than its liquid form, bodies of water in colder climates do not freeze solid in winter.
Allows life to flourish under the ice.

42. Water’s Structure Gives It Many Unusual Properties
ice
In ice, the maximum number
of hydrogen bonds form,
causing the molecules to be
spread far apart.
liquid
water
In liquid water, hydrogen
bonds constantly break and
re-form, enabling a more
dense spacing than in ice.
Figure 2.16

43. Water’s Structure Gives It Many Unusual Properties
Water has a great capacity to absorb and retain heat.
Because of this, the oceans act as heat buffers for the Earth, thus stabilizing Earth’s temperature.

44. Water’s Structure Gives It Many Unusual Properties
Water has a high degree of cohesion, which allows water to be drawn up through plants, via evaporation, in one continuous column, from roots through leaves.

45. Hydrophobic and Hydrophilic
Some compounds do not interact with water.
Hydrocarbons such as petroleum are examples of such hydrophobic compounds.
Water cannot break down hydrophobic compounds, which is why oil and water don’t mix.

46. Hydrophobic and Hydrophilic
Figure 2.17

47. Hydrophobic and Hydrophilic
Compounds that interact with water are polar or carry an electric charge and are called hydrophilic compounds.

48. 2.5 Acids and Bases Are Important to Life

49. Acids and Bases Are Important to Life
An acid is any substance that yields hydrogen ions when put in aqueous solution.
A base is any substance that accepts hydrogen ions in solution.

50. Acids and Bases
A base added to an acidic solution makes that solution less acidic.
An acid added to a basic solution makes that solution less basic.

51. Acids and Bases Figure 2.18 pure water (a) Starting with pure water
Pure water is a “neutral”
substance in terms of its
pH levels.
(H2O)
(b) Making water
more acidic
(c) Making water
more basic
HCl
NaOH
Hydrochloric acid (HCl),
poured into the water,
dissociates into
H+ and Cl- ions.
With a higher
concentration of
H+ ions in it, the
water moves
towards the
acidic end of the
pH scale.
An equal concentration of
sodium hydroxide, poured into water,
dissociates into Na+ and OH– ions,
moving the water toward the basic
end of the scale.
(d) Combining acidic and basic
solutions
When the acid and base solutions
are poured together, the OH– ions
from (c) accept the H+ ions from
(b), forming water and keeping
the solution at a neutral pH.
acid base
neutralized
solution
Figure 2.18

52. Acids and Bases
The concentration of hydrogen ions that a given solution has determines how basic or acidic that solution is.
The pH scale measures acidity.
This scale runs from 0 to 14, with 0 most acidic,14 the most basic, and 7 neutral.

53. Acids and Bases Figure 2.19 H+ concentration (moles/liter) pH acidic
battery acid
hydrochloric acid
lemon juice, gastric
(stomach) juice
cola, beer, wine, vinegar
tomatoes
black coffee
urine
neutral
water
human blood
seawater
human
blood is
slightly
basic
baking soda
Great Salt Lake
household
ammonia
household bleach
oven cleaner
lye
basic
Figure 2.19

54. Acids and Bases The pH scale is logarithmic.
A substance with a pH of 9 is 10 times as basic as a substance with a pH of 8

55. Acids and Bases
Living things function best in a near-neutral pH, although some systems in living things have different pH requirements.

56. Acids and Bases
PLAY
Animation 2.4: Water and pH