fundamental building blocks: chemistry, water, and ph
TRANSCRIPT
Fundamental Building Blocks:Chemistry, Water, and pH
2.1 Chemistry’s Building Block: The Atom
Chemistry’s Building Block: The Atom
• The fundamental unit of matter is the atom.
Protons, Neurons, and Electrons
• The three most important constituent parts of an atom are – protons – neutrons – electrons
Protons, Neurons, and Electrons
• Protons and neutrons exist in the atom’s nucleus, while electrons move around the nucleus, at some distance from it.
Chapter 2 Lecture
Figure 2.2
electronshell
electron(negative charge)
proton(positive charge)
neutron(no charge)
nucleus
Hydrogen (H) Helium (He)
Protons, Neurons, and Electrons
• Protons are positively charged.
• Electrons are negatively charged.
• Neutrons carry no charge.
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.
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.
The Element
Figure 2.5
1 proton1 neutron
1 proton0 neutrons
1 proton2 neutrons
Hydrogen Deuterium Tritium
The Element
PLAYPLAY Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 1: Animation
PLAYPLAY Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 2: Exercise 1
PLAYPLAY Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 3: Exercise 2
The Element
• Protons are positively charged.
• Electrons are negatively charged.
• Neutrons carry no charge.
2.2 Matter is Transformed Through Chemical Bonding
Matter is Transformed Through Chemical Bonding
• Atoms can link to one another in the process of chemical bonding.
Covalent Bond
• Covalent bond: atoms share one or more electrons
• Ionic bond: atoms lose and accept electrons from each other
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.
Covalent Bond
• Hydrogen and helium require two electrons in orbit around their nuclei to have filledouter shells.
• Most other elements require eight electrons to have filled outer shells.
Covalent Bond
Figure 2.7
hydrogen (H)
carbon (C)
sodium (Na)
helium (He)
neon (Ne)
argon (Ar)
Unstable, very reactive atoms Stable, unreactive atoms
Outermost electronshells unfilled
Outermost electronshells filled
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.
Covalent Bond
Figure 2.8
hydrogen (H)atom
hydrogen (H)atom
oxygen (O)atom
hydrogen (H)atom
hydrogen (H)atom
oxygen (O)atom
(b) One water molecule(a) Two hydrogen atoms and one oxygen atom
Covalent Bond
• Atoms of different elements differ in their power to attract electrons.
• The term for measuring this power is electronegativity.
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.
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.
Polar and Nonpolar Bonding
Figure 2.9
polar
nonpolarbecausecharges aresymmetric
slightnegativecharge
slightpositivecharge
(a) Polar water molecule (b) Nonpolar methane molecule
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.
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.
Ionic Bonding
Figure 2.10
sodium atom (Na) chlorine atom (Cl)
chloride ion(Cl–)
sodium ion (Na+)
electrontransfer
ioniccompound(Na+Cl–)
salt crystals
(a) Initial instabilitySodium has buta single electronin its outer shell,while chlorine has seven, meaningit lacks only a single electron to have acompleted outer shell.
(b) Electron transferWhen these twoatoms cometogether, sodiumloses its third-shellelectron to chlorine,in the processbecoming a sodiumion with a netpositive charge(because it now hasmore protons thanelectrons). Havinggained an electron,the chlorine atombecomes a chlorideion, with a netnegative charge(because it hasmore electronsthan protons).
(c) Ionic attractionThe sodium and chlorideions are now attracted toeach other because theyare oppositely charged.
(d) Compound formationThe result of this electrostaticattraction, involving manysodium and chloride ions, is asodium chloride crystal (NaCl),better known as table salt.
Hydrogen Bonding
• Hydrogen bonding links an already covalently bonded hydrogen atom with an electronegative atom.
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.
Hydrogen Bonding
Figure 2.11
hydrogen bond
Hydrogen Bonding
PLAYPLAY Animation 2.2: Chemical Bonding
2.3 Some Qualities of Chemical Compounds
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.
Molecular Shape
Figure 2.13
good fit,scent issmelled
signalto brain
receptormolecules
cells of nasalpassage
signal molecules(aroma from bread)
bad fit,scent is notsmelled
Molecular Shape
PLAYPLAY Animation 2.3: Geometry, Chemistry, and Biology
2.4 Water and Life
Water and Life
• Water has several qualities that have strongly affected life on Earth.
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.
Water is a Major Player in Many of Life’s Processes
Figure 2.15
water(solvent)
sodiumchloride(solute)
Sodium andchloride ionsdissolvedin water
Sodium chloride’spositively chargedsodium ions (Na+) areattracted to water’snegatively chargedoxygen atoms, whileits negatively chargedchloride ions (Cl–) areattracted to water’spositively chargedhydrogen atoms.
Pulled from the crystal,and separated fromeach other by thisattraction, sodium andchloride ions becomesurrounded by watermolecules.
This process ofseparating sodium andchloride ions repeatsuntil both ions areevenly dispersed,making this an aqueoussolution.
(a) Attraction (b) Separation (c) Dispersion
OH
H
Cl–Na+
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.
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.
Water’s Structure Gives It Many Unusual Properties
Figure 2.16
ice
liquidwater
In ice, the maximum numberof hydrogen bonds form,causing the molecules to bespread far apart.
In liquid water, hydrogenbonds constantly break andre-form, enabling a moredense spacing than in ice.
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.
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.
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.
Hydrophobic and Hydrophilic
Figure 2.17
Hydrophobic and Hydrophilic
• Compounds that interact with water are polar or carry an electric charge and are called hydrophilic compounds.
2.5 Acids and Bases Are Important to Life
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.
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.
Acids and Bases
Figure 2.18
acid base
NaOHHCl
(H2O)
(a) Starting with pure water
(b) Making water more acidic
(c) Making water more basic
(d) Combining acidic and basic solutions
neutralizedsolution
Hydrochloric acid (HCl),poured into the water,dissociates intoH+ and Cl- ions.With a higherconcentration ofH+ ions in it, thewater movestowards theacidic end of thepH scale.
When the acid and base solutionsare poured together, the OH– ionsfrom (c) accept the H+ ions from(b), forming water and keepingthe solution at a neutral pH.
An equal concentration ofsodium hydroxide, poured into water,dissociates into Na+ and OH– ions,moving the water toward the basicend of the scale.
Pure water is a “neutral”substance in terms of itspH levels.
pure water
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.
Acids and Bases
Figure 2.19
hydrochloric acid
lemon juice, gastric(stomach) juice
cola, beer, wine, vinegar
tomatoes
black coffee
urine
water
seawater
baking soda
Great Salt Lake
household ammonia
household bleach
oven cleaner
lye
battery acid
humanblood isslightlybasic
human blood
basic
acidic pH
H+ concentration(moles/liter)
neutral
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
Acids and Bases
• Living things function best in a near-neutral pH, although some systems in living things have different pH requirements.
Acids and Bases
PLAYPLAY Animation 2.4: Water and pH