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 areprotonsneutronselectrons
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)nucleusneutron(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 ElementAn 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 ElementThe 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: AnimationPLAYAnimation 2.1: Structure of Atoms, Elements, Isotopes: Part 2: Exercise 1PLAYAnimation 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 BondChemical 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 BondHydrogen 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.
19 Covalent BondA 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)atomhydrogen (H)atomhydrogen (H)atomhydrogen (H)atomoxygen (O)atomoxygen (O)atom(a) Two hydrogen atoms and one oxygen atom(b) One water moleculeFigure 2.8
21 Covalent BondAtoms 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 moleculeslightnegativechargepolarnonpolarbecausecharges aresymmetricslightpositivechargeFigure 2.9
25 Ionic BondingTwo 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 BondingThe 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 instabilitySodium has buta single electronin its outer shell,while chlorinehas seven, meaningit lacks only a singleelectron to have acompleted outershell.electrontransfer(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).chloride ion(Cl–)sodium ion (Na+)ioniccompound(Na+Cl–)(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.salt crystalsFigure 2.10
28 Hydrogen BondingHydrogen bonding links an already covalently bonded hydrogen atom with an electronegative atom.
29 Hydrogen BondingIn water, a hydrogen atom of one water molecule will form a hydrogen bond with an unshared oxygen electron of a neighboring water molecule.
37 Water and LifeWater 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) Dispersionwater (solvent)Sodium and chloride ions dissolved in waterHOHNa+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 iceIn ice, the maximum numberof hydrogen bonds form,causing the molecules to bespread far apart.liquidwaterIn liquid water, hydrogenbonds constantly break andre-form, enabling a moredense 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.
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 BasesA 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 itspH levels.(H2O)(b) Making watermore acidic(c) Making watermore basicHClNaOHHydrochloric 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.An equal concentration ofsodium hydroxide, poured into water,dissociates into Na+ and OH– ions,moving the water toward the basicend of the scale.(d) Combining acidic and basicsolutionsWhen 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.acid baseneutralizedsolutionFigure 2.18
52 Acids and BasesThe 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.