Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Phones must be put away now, no earbuds, no texting Do you have anything to turn in to green basket?

Chapter 2: Chemical Context of Life Atoms and Molecules Atoms and Molecules Chapter 2: Chemical Context of Life Atoms and Molecules Atoms and Molecules

Elements and Compounds Organisms are composed of matter, which is anything that takes up space and has mass Matter is made up of elements, substances that cannot be broken down to other substances by chemical reactions 92 unique elements exist in nature More have been created in the lab More have been created in the lab Organisms are composed of matter, which is anything that takes up space and has mass Matter is made up of elements, substances that cannot be broken down to other substances by chemical reactions 92 unique elements exist in nature More have been created in the lab More have been created in the lab

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Compounds SodiumChloride Sodium Chloride + A compound Is a substance consisting of two or more elements combined in a fixed ratio Has characteristics different from those of its elements

Essential Elements of Life Essential elements Include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Make up 96% of living matter Make up 96% of living matter Essential elements Include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Make up 96% of living matter Make up 96% of living matter

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Other Elements A few other elements make up the remaining 4% of living matter

Each element Consists of a certain kind of atom that is different from those of other elements An atom Is the smallest unit of matter that still retains the properties of an element Each element Consists of a certain kind of atom that is different from those of other elements An atom Is the smallest unit of matter that still retains the properties of an element Elements

Subatomic Particles Atoms of each element are composed of even smaller parts called subatomic particles Atoms of each element are composed of even smaller parts called subatomic particles Relevant subatomic particles include Relevant subatomic particles include Neutrons, which have no electrical charge Neutrons, which have no electrical charge Protons, which are positively charged Protons, which are positively charged Electrons, which are negatively charged Electrons, which are negatively charged Atoms of each element are composed of even smaller parts called subatomic particles Atoms of each element are composed of even smaller parts called subatomic particles Relevant subatomic particles include Relevant subatomic particles include Neutrons, which have no electrical charge Neutrons, which have no electrical charge Protons, which are positively charged Protons, which are positively charged Electrons, which are negatively charged Electrons, which are negatively charged

Subatomic Particles Protons and neutrons Are found in the atomic nucleus Electrons Surround the nucleus in a “cloud” Protons and neutrons Are found in the atomic nucleus Electrons Surround the nucleus in a “cloud”

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Model of the Atom Nucleus (a) (b) In this even more simplified model, the electrons are shown as two small blue spheres on a circle around the nucleus. Cloud of negative charge (2 electrons) Electrons This model represents the electrons as a cloud of negative charge, as if we had taken many snapshots of the 2 electrons over time, with each dot representing an electron‘s position at one point in time. Simplified models of an atom

Atomic Number and Atomic Mass Atoms of the various elements Differ in their number of subatomic particles Differ in their number of subatomic particles The atomic number of an element Is the number of protons Is the number of protons Is unique to each element Is unique to each element The mass number of an element Is the sum of protons plus neutrons in the nucleus of an atom Is the sum of protons plus neutrons in the nucleus of an atom Is an approximation of the atomic mass of an atom Is an approximation of the atomic mass of an atom Atoms of the various elements Differ in their number of subatomic particles Differ in their number of subatomic particles The atomic number of an element Is the number of protons Is the number of protons Is unique to each element Is unique to each element The mass number of an element Is the sum of protons plus neutrons in the nucleus of an atom Is the sum of protons plus neutrons in the nucleus of an atom Is an approximation of the atomic mass of an atom Is an approximation of the atomic mass of an atom

IsotopesIsotopes Atoms of a given element may occur in different forms called Isotopes Atoms of a given element may occur in different forms called Isotopes Isotopes of a given element Isotopes of a given element Differ in the number of neutrons in the atomic nucleus Differ in the number of neutrons in the atomic nucleus Have the same number of protons Have the same number of protons Radioactive isotopes Radioactive isotopes Spontaneously give off particles and energy Spontaneously give off particles and energy Atoms of a given element may occur in different forms called Isotopes Atoms of a given element may occur in different forms called Isotopes Isotopes of a given element Isotopes of a given element Differ in the number of neutrons in the atomic nucleus Differ in the number of neutrons in the atomic nucleus Have the same number of protons Have the same number of protons Radioactive isotopes Radioactive isotopes Spontaneously give off particles and energy Spontaneously give off particles and energy

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Radioactive Isotopes Can be used in biology and medicine Cancerous throat tissue

Energy Levels of Electrons An atom’s electrons Vary in the amount of energy they possess Vary in the amount of energy they possessEnergy Is defined as the capacity to cause change Is defined as the capacity to cause change Potential energy Is the energy that matter possesses because of its location or structure Is the energy that matter possesses because of its location or structure An atom’s electrons Vary in the amount of energy they possess Vary in the amount of energy they possessEnergy Is defined as the capacity to cause change Is defined as the capacity to cause change Potential energy Is the energy that matter possesses because of its location or structure Is the energy that matter possesses because of its location or structure

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Energy Levels The electrons of an atom Differ in the amounts of potential energy they possess A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons, because the ball can only rest on each step, not between steps. (a)

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Electron Shells Energy levels Are represented by electron shells Third energy level (shell) Second energy level (shell) First energy level (shell) Energy absorbed Energy lost 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. (b) Atomic nucleus

Electron Configuration and Chemical Properties Valence electrons Are those in the outermost, or valence shell Are those in the outermost, or valence shell Determines the chemical behavior of an atom Determines the chemical behavior of an atom The valence number of an atom is the number of unpaired electrons in its valence shell This valence number determines the number of bonds the atom can form. Valence electrons Are those in the outermost, or valence shell Are those in the outermost, or valence shell Determines the chemical behavior of an atom Determines the chemical behavior of an atom The valence number of an atom is the number of unpaired electrons in its valence shell This valence number determines the number of bonds the atom can form.

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Periodic Table (Campbell & Reece, p.32) The periodic table of the elements Shows the electron distribution for all the elements Shows the electron distribution for all the elements Second shell Helium 2 He First shell Third shell Hydrogen 1 H 2 He 4.00 Atomic mass Atomic number Element symbol Electron-shell diagram Lithium 3 Li Beryllium 4 Be Boron 3 B Carbon 6 C Nitrogen 7 N Oxygen 8 O Fluorine 9 F Neon 10 Ne Sodium 11 Na Magnesium 12 Mg Aluminum 13 Al Silicon 14 Si Phosphorus 15 P Sulfur 16 S Chlorine 17 Cl Argon 18 Ar

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Which drawing depicts an atom with a valence of 2? a.A b.B c.C d.D e.E

OrbitalsOrbitals An orbital Is the three-dimensional space where an electron is found 90% of the time Is the three-dimensional space where an electron is found 90% of the time An orbital Is the three-dimensional space where an electron is found 90% of the time Is the three-dimensional space where an electron is found 90% of the time

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Orbitals Each electron shell Consists of a specific number of orbitals Consists of a specific number of orbitals Electron orbitals. Each orbital holds up to two electrons. 1s orbital2s orbitalThree 2p orbitals 1s, 2s, and 2p orbitals (a) First shell (maximum 2 electrons) (b) Second shell (maximum 8 electrons) (c) Neon, with two filled shells (10 electrons) Electron-shell diagrams. Each shell is shown with its maximum number of electrons, grouped in pairs. x Z Y

Filling pattern of electron orbitals: Electrons fill lower shells first before outer shells First: two electrons in 1s orbital First: two electrons in 1s orbital Then: two electrons 2s orbital Then: two electrons 2s orbital Then: one electron in each of 2p orbitals before adding more to any 2p if necessary Then: one electron in each of 2p orbitals before adding more to any 2p if necessary Carbon breaks these rules: sp 3 hybridization Allows 4 unpaired electrons = 4 bonds Allows 4 unpaired electrons = 4 bonds Filling pattern of electron orbitals: Electrons fill lower shells first before outer shells First: two electrons in 1s orbital First: two electrons in 1s orbital Then: two electrons 2s orbital Then: two electrons 2s orbital Then: one electron in each of 2p orbitals before adding more to any 2p if necessary Then: one electron in each of 2p orbitals before adding more to any 2p if necessary Carbon breaks these rules: sp 3 hybridization Allows 4 unpaired electrons = 4 bonds Allows 4 unpaired electrons = 4 bonds Orbitals

online.com/objects/index_tj.asp?objid=G CH904 online.com/objects/index_tj.asp?objid=G CH904 online.com/objects/index_tj.asp?objid=G CH904 online.com/objects/index_tj.asp?objid=G CH904 Structure of an Atom

BondsBonds The formation and function of molecules depend on chemical bonding between atoms. The formation and function of molecules depend on chemical bonding between atoms.

BondsBonds A covalent bond A covalent bond Is the sharing of a pair of valence electrons Is the sharing of a pair of valence electrons The formation and function of molecules depend on chemical bonding between atoms. The formation and function of molecules depend on chemical bonding between atoms. A covalent bond A covalent bond Is the sharing of a pair of valence electrons Is the sharing of a pair of valence electrons

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Covalent Bonds Formation of a covalent bond Hydrogen atoms (2 H) Hydrogen molecule (H 2 ) In each hydrogen atom, the single electron is held in its orbital by its attraction to the proton in the nucleus. 1 When two hydrogen atoms approach each other, the electron of each atom is also attracted to the proton in the other nucleus. 2 The two electrons become shared in a covalent bond, forming an H 2 molecule. 3

A molecule Consists of two or more atoms held together by covalent bonds Consists of two or more atoms held together by covalent bonds A single bond Is the sharing of one pair of valence electrons Is the sharing of one pair of valence electrons A double bond Is the sharing of two pairs of valence electrons Is the sharing of two pairs of valence electrons A molecule Consists of two or more atoms held together by covalent bonds Consists of two or more atoms held together by covalent bonds A single bond Is the sharing of one pair of valence electrons Is the sharing of one pair of valence electrons A double bond Is the sharing of two pairs of valence electrons Is the sharing of two pairs of valence electrons Covalent Bonds

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Covalent Bonds (a) (b) Name (molecular formula) Electron- shell diagram Structural formula Space- filling model Hydrogen (H 2 ). Two hydrogen atoms can form a single bond. Oxygen (O 2 ). Two oxygen atoms share two pairs of electrons to form a double bond. HH O O Single and double covalent bonds

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Covalent Bonds Name (molecular formula) Electron- shell diagram Structural formula Space- filling model (c) Methane (CH 4 ). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. Water (H 2 O). Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. (d) H O H HH H H C Covalent bonding in molecules

ElectronegativityElectronegativity Electronegativity Is the attraction of a particular kind of atom for the electrons in a covalent bond Is the attraction of a particular kind of atom for the electrons in a covalent bond The more electronegative an atom The more strongly it pulls shared electrons toward itself The more strongly it pulls shared electrons toward itself In a nonpolar covalent bond The atoms have similar electronegativities The atoms have similar electronegativities Share the electron equally Share the electron equallyElectronegativity Is the attraction of a particular kind of atom for the electrons in a covalent bond Is the attraction of a particular kind of atom for the electrons in a covalent bond The more electronegative an atom The more strongly it pulls shared electrons toward itself The more strongly it pulls shared electrons toward itself In a nonpolar covalent bond The atoms have similar electronegativities The atoms have similar electronegativities Share the electron equally Share the electron equally

Thinking Question Electronegativity values increase as the atom becomes smaller and as you go from left to right on the Periodic Table. Why do you think this is so?

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Polar Covalent Bonds This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. H2OH2O –– O H H ++ ++ Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. In a polar covalent bond The atoms have differing electronegativities Share the electrons unequally

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Water Models This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. H2OH2O –– O H H ++ ++ Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. Make 10 or more paper cut-outs of water atomsMake 10 or more paper cut-outs of water atoms Arrange them to demonstrate water crystal latticeArrange them to demonstrate water crystal lattice

Covalent Bonds Reviewed

Ionic Bonds In some cases, atoms strip electrons away from their bonding partners Electron transfer between two atoms creates ions Ions Are atoms with more or fewer electrons than usual (charged atoms) Are atoms with more or fewer electrons than usual (charged atoms) Such as Na +, Cl -, K +, PO 4 3- Such as Na +, Cl -, K +, PO 4 3- In some cases, atoms strip electrons away from their bonding partners Electron transfer between two atoms creates ions Ions Are atoms with more or fewer electrons than usual (charged atoms) Are atoms with more or fewer electrons than usual (charged atoms) Such as Na +, Cl -, K +, PO 4 3- Such as Na +, Cl -, K +, PO 4 3-

Ionic Bonds An anion Atom that gains electrons Atom that gains electrons Is negatively charged Is negatively charged Cl -, PO 4 3- Cl -, PO 4 3- A cation Atom that lost electrons Atom that lost electrons Is positively charged Is positively charged Na +, K + Na +, K + An anion Atom that gains electrons Atom that gains electrons Is negatively charged Is negatively charged Cl -, PO 4 3- Cl -, PO 4 3- A cation Atom that lost electrons Atom that lost electrons Is positively charged Is positively charged Na +, K + Na +, K +

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Ionic Bonds Cl – Chloride ion (an anion) – The lone valence electron of a sodium atom is transferred to join the 7 valence electrons of a chlorine atom. 1 Each resulting ion has a completed valence shell. An ionic bond can form between the oppositely charged ions. 2 Na Cl + Na Sodium atom (an uncharged atom) Cl Chlorine atom (an uncharged atom) Na + Sodium on (a cation) Sodium chloride (NaCl) An ionic bond Is an attraction between anions and cations

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Ionic Bonds Na + Cl – Ionic compounds Are often called salts, which may form crystals

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen Bonds  – –  + +  + + Water (H 2 O) Ammonia (NH 3 ) O H H  + +  – – N H H H 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. ++ ++ A hydrogen bond Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom

Molecular Shape and Function The precise shape of a molecule Is usually very important to its function in the living cell Is usually very important to its function in the living cell Is determined by the positions of its atoms’ valence orbitals Is determined by the positions of its atoms’ valence orbitals The precise shape of a molecule Is usually very important to its function in the living cell Is usually very important to its function in the living cell Is determined by the positions of its atoms’ valence orbitals Is determined by the positions of its atoms’ valence orbitals

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Molecular Shape Space-filling model Hybrid-orbital model (with ball-and-stick model superimposed) Unbonded Electron pair 104.5° O H Water (H 2 O) Methane (CH 4 ) H H H H C O H H H C Ball-and-stick model H H H H

Chemical Reactions Chemical reactions Are the making and breaking of chemical bonds Are the making and breaking of chemical bonds Lead to changes in the composition of matter Lead to changes in the composition of matter Chemical reactions Are the making and breaking of chemical bonds Are the making and breaking of chemical bonds Lead to changes in the composition of matter Lead to changes in the composition of matter

Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Chemical Reactions Reactants ReactionProduct 2 H 2 O2O2 2H 2 O + + Chemical reactions Convert reactants to products

EquilibriumEquilibrium Chemical equilibrium Is reached when the forward and reverse reaction rates are equal Is reached when the forward and reverse reaction rates are equal Chemical equilibrium Is reached when the forward and reverse reaction rates are equal Is reached when the forward and reverse reaction rates are equal

Key Points of Chapter 2 Matter consists of chemical elements in pure form and in combinations called compounds Matter consists of chemical elements in pure form and in combinations called compounds An element’s properties depend on the structure of its atoms An element’s properties depend on the structure of its atoms The formation and function of molecules depends on chemical bonding between atoms The formation and function of molecules depends on chemical bonding between atoms Chemical reactions make and break chemical bonds Chemical reactions make and break chemical bonds Matter consists of chemical elements in pure form and in combinations called compounds Matter consists of chemical elements in pure form and in combinations called compounds An element’s properties depend on the structure of its atoms An element’s properties depend on the structure of its atoms The formation and function of molecules depends on chemical bonding between atoms The formation and function of molecules depends on chemical bonding between atoms Chemical reactions make and break chemical bonds Chemical reactions make and break chemical bonds