2 Elements and Compounds An element is a substance that cannot be broken down to other substances by chemical reactions (pure)CarbonOxygenA compound is a substance consisting of two or more elements in a fixed ratioSodium chloride
3 Essential Elements of Life About 25 of the 92 elements are essential to lifeCarbon, hydrogen, oxygen, and nitrogen make up 96% of living matterMost of the remaining 4% consists of calcium, phosphorus, potassium, and sulfurTrace elements are those required by an organism in minute quantities
5 Trace elements are elements that are necessary, but present in very small quantities Sulphur: an important element in some amino acids.Calcium: used during nerve impulsesIron: found in hemoglobin (oxygen transport protein)Sodium: needed for a nerve impulsePhosphorus: in cell membrane structures and DNA
6 An element’s properties depend on the structure of its atoms Each element consists of unique atomsAn atom is the smallest unit of matter that still retains the properties of an element
7 Subatomic Particles Atoms are composed of subatomic particles Relevant subatomic particles include:Neutrons (no electrical charge)Protons (positive charge)Electrons (negative charge)# protons = atomic number# protons + # neutrons = mass number# protons = # electronsElectrons form a cloud around the nucleus
8 Cloud of negative charge (2 electrons) Electrons Nucleus (a) (b) Fig. 2-5Cloud of negativecharge (2 electrons)ElectronsNucleusFigure 2.5 Simplified models of a helium (He) atom(a)(b)
9 The formation and function of molecules depend on chemical bonding between atoms Atoms with incomplete valence shells can share or transfer valence electrons with certain other atomsThese interactions usually result in atoms staying close together, held by attractions called chemical bonds
12 Electrons in a covalent bond may be equally or unequally shared between the atoms Non-polar covalent bond: atoms share electrons evenlyPolar covalent bond: atoms share electrons unequally, so there is a slight difference in charge between the two poles of the bond
14 Polar Covalent Bond A molecule with polar bonds may be polar overall H2O is a polar moleculeThe (slightly) positively charged pole is around each hydrogenThe (slightly) negatively charged pole is around the oxygen
16 Ionic BondsWhen atom loses or gains an electron, it becomes an positively or negatively charged IONCations are positively charged (because they have fewer electrons than protons). They are giving away their electrons.Anions are negatively charged (because they have more electrons than protons) They are receiving the electrons.
17 Animation: Ionic/Covalent Bonds In an ionic bond, cations and anions are linked by attraction of opposite chargesNaClNaClNaClNa+Cl–Sodium atomChlorine atomSodium ion(a cation)Chloride ion(an anion)Figure 2.14 Electron transfer and ionic bondingSodium chloride (NaCl)Animation: Ionic/Covalent Bonds
19 Most biological molecules contain covalent bonds Covalent bonds are stronger than ionic bonds but vary in their stability
20 Hydrogen BondsPolar molecules like water have partially charged atoms at their endsHydrogen bonds form when partial opposite charges in different molecules attract each otherThe partially positive hydrogens of one water molecule are attracted to the partially negative oxygen on another
22 Hydrogen Bonds…Weak bond that is easily broken because no electrons are sharedImportant in stabilizing the 3D shape of large molecules like proteins and DNA
23 Chemical reactions make and break chemical bonds Chemical reactions are the making and breaking of chemical bondsThe starting molecules of a chemical reaction are called reactantsThe final molecules of a chemical reaction are called products2 H2O22 H2OReactionReactantsProducts
24 Do atoms always have an equal number of protons, neutrons and electrons? 1. Yes.2. No.
25 A chemical bond is formed through: 1. The gaining, losing, or sharing of protons.2. The gaining, losing, or sharing of neutrons.3. The gaining, losing, or sharing of electrons.4. The gaining, losing, or sharing of isotopes.5. The gaining, losing, or sharing of ions.
26 After sodium loses an electron, it is: 1. A positive ion.2. A negative ion.3. A neutral ion.4. An isotope.5. A compound.
27 After chlorine gains an electron, it is: 1. A positive ion.2. A negative ion.3. A neutral ion.4. An isotope.5. A compound.
28 What is the difference between a nonpolar covalent bond and a polar covalent bond? 1. A polar covalent bond results when there is unequal sharing of electrons in a molecule, whereas electrons are shared equally in a nonpolar covalent bond. 2. A polar covalent bond has two equal sides and a nonpolar covalent bond has two different sides. 3. A nonpolar covalent bond is positively charged and a polar covalent bond is negatively charged. 4. A polar covalent bond is positively charged and a nonpolar covalent bond is negatively charged.
29 Why Is Carbon So Important? Organic vs. Inorganic in ChemistryOrganic refers to molecules containing a carbon skeletonInorganic refers to carbon dioxide and all molecules without carbon
30 Carbon atoms are versatile and can form up to four bonds (single, double, or triple) and rings Functional groups in organic molecules confer chemical reactivity and other characteristicsFunctional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules
36 Organic Molecule Synthesis Monomers are joined together through condensation reactions.An H and an OH are removed, resulting in the loss of a water molecule (H2O)Also called dehydration synthesis (but IB uses the word condensation)
39 Organic Molecule Synthesis Polymers are broken apart through hydrolysis (“water cutting”)Water is broken into H and OH and used to break the bond between monomersHydrolysis is the reverse of condensation: one molecule is split by the addition of H+ and OH- (from water) to the components.