Atoms Smallest electrically neutral particle of an element that retains the properties of that element.

Democritus 4 th century B.C. in Greece Indestructible & indivisible tiny particles called atoms

John Dalton ( ) English Experimental evidence Ratios in which elements combine in chemical reactions

Dalton’s atomic theory  All elements are composed of tiny indivisible particles called atoms.

Dalton’s atomic theory  Atoms of the same element are identical. The atoms of any 1 element are different from those of any other element.

Dalton’s atomic theory  Atoms of different elements can physically mix together or can chemically combine w/ one another in simple whole- number ratios to from compounds.

Dalton’s atomic theory  Chemical reactions occur when atoms are separated, joined, or re-arranged. Atoms of one element, however, are never changed into atoms of another element as a result of chemical rxns.

Error in Dalton’s Atomic Theory  atoms are divisible  now can identify subatomic particles

Just How Small is an Atom  copper atoms lined up 1 cm long = 10 7 = Cu atoms  Approximately the width of a penny.

Atomic Structure  Atoms composed of e -, p +, n o  Nucleus is p + & n o

Electrons  Negatively charged subatomic particles  J.J. Thompson discovered in 1897

Protons  Protons in atoms are equal to # of electrons  Have ‘+1’ charge  Mass ‘1840x’ an electron

Neutrons  Have no charge  Same relative mass as proton

Atomic Number  Atomic number is # of p + in nucleus of atom  Elements different because different # of protons –# p + = #e - in atom –H= 1 p e - –O= 8p + + 8e -

Periodic Table

Mass Number  The sum of p + + n o = mass #  If have atomic # + mass # of an atom of any element you can find composition  Shorthand notation for composition of atom – mass# Symbol – atomic# 197 Au 79

Isotopes  Atoms w/ same # of p + but different # of n o  Also has different mass #

Isotopes  Despite this difference they are chemically alike  Same # of p + + e -  P + + e - are responsible for chemical behavior

H and C Isotopes

Atomic Mass Calculation  Atomic Mass takes into account relative abundance of isotopes  In nature each isotope of an element has a fixed mass  In nature each isotope of an element has a natural % abundance

Periodic Table

Atoms: The Constituents of Matter  Electrons are distributed in shells of orbitals containing a maximum of two. Review Figures 2.4,

2.4 Figure 2.4 figure jpg

2.5 Figure 2.5 figure jpg

Atoms: The Constituents of Matter  An atom can combine with other atoms to form molecules. Review Table

Chemical Bonds: Linking Atoms Together  Covalent bonds form when two atomic nuclei share one or more pairs of electrons. They have spatial orientations that give molecules three-dimensional shapes. Review Figures 2.6, 2.7, Table

2.6 Figure 2.6 figure jpg

2.7 Figure 2.7 figure jpg

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Chemical Bonds: Linking Atoms Together  Nonpolar covalent bonds form when the electronegativities of two atoms are approximately equal. When atoms with strong electronegativity (such as oxygen) bond to atoms with weaker electronegativity (such as hydrogen), a polar covalent bond forms, in which one end is  + and the other is  –. Review Figure 2.8, Table

2.8 Figure 2.8 figure jpg

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Chemical Bonds: Linking Atoms Together  Hydrogen bonds form between a  + hydrogen atom in one molecule and a  – nitrogen or oxygen atom in another molecule or in another part of a large molecule. Review Figure

Figure 2.9 figure jpg

Chemical Bonds: Linking Atoms Together  Ions, electrically charged bodies, form when an atom gains or loses one or more electrons. Ionic bonds are electrical attractions between oppositely charged ions. Review Figures 2.10,

2.10 Figure 2.10 figure jpg

2.11 Figure 2.11 figure jpg

Chemical Bonds: Linking Atoms Together  Nonpolar molecules do not interact directly with polar substances. They are attracted to each other by very weak bonds called van der Waals forces. Review Figure

Figure 2.12 figure jpg

Chemical Reactions: Atoms Change Partners  In chemical reactions, substances change their atomic compositions and properties. Energy is either released or added. Matter and energy are not created or destroyed, but change form.

Chemical Reactions: Atoms Change Partners  Combustion reactions are oxidation- reduction reactions. Fuel is converted to carbon dioxide and water, while energy is released as heat and light. In living cells, these reactions occur in multiple steps. Review Figure

Figure 2.13 figure jpg

Water: Structure and Properties  Water’s molecular structure and capacity to form hydrogen bonds give it unusual properties significant for life. Review Figure

Figure 2.15 figure jpg

Water: Structure and Properties  Cohesion of water molecules results in a high surface tension. Water’s high heat of vaporization assures cooling when it evaporates.

Water: Structure and Properties  Solutions are substances dissolved in water. Concentration is the amount of a given substance in a given amount of solution. Most biological substances are dissolved at very low concentrations.

Acids, Bases, and the pH Scale  Acids are substances that donate hydrogen ions. Bases are those that accept hydrogen ions.

Acids, Bases, and the pH Scale  The pH of a solution is the negative logarithm of the hydrogen ion concentration. Values lower than pH 7 indicate an acidic solution. Values above pH 7 indicate a basic solution. Review Figure

Figure 2.18 figure jpg

Acids, Bases, and the pH Scale  Buffers are systems of weak acids and bases that limit the change in pH when hydrogen ions are added or removed. Review Figure

Figure 2.19 figure jpg

The Properties of Molecules  Molecules vary in size, shape, reactivity, solubility, and other chemical properties.

The Properties of Molecules  Functional groups make up part of a larger molecule and have particular chemical properties.

The Properties of Molecules  The consistent chemical behavior of functional groups helps us understand the properties of the molecules that contain them. Review Figure

2.20 – Part 1 Figure 2.20 – Part 1 figure 02-20a.jpg

2.20 – Part 2 Figure 2.20 – Part 2 figure 02-20b.jpg

The Properties of Molecules  Structural and optical isomers have the same kinds and numbers of atoms, but differ in their structures and properties. Review Figure

Figure 2.21 figure jpg

Osmosis and Diffusion

Condensation Reactions  Longer polymer chains are formed and water is a product.  OH and H are separated from smaller molecules to form larger polymers.  Also called Dehydration Reactions.

Hydrolysis Reactions  Water is separated to free a hydroxide group and a hydrogen ion to join to create smaller polymers.

Life: The Science of Biology 6th ed William K Purves, David Sadava, Gordon H Orians, H Craig Heller, Sinauer Associates, Inc., 2001