Atoms

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

element.

Democritus

4th century B.C. in GreeceIndestructible & indivisible tiny particles

called atoms

John Dalton

(1766-1844) EnglishExperimental 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 = 107 = 100 000 000. Cu atoms

Approximately the width of a penny.

Atomic Structure

Atoms composed of e-, p+, no

Nucleus is p+ & no

Electrons

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

Protons

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

Neutrons

Have no chargeSame 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+ + 1 e-

– O= 8p+ + 8e-

Periodic Table

Mass Number

The sum of p++ no= mass # If have atomic # + mass # of an atom of any

element you can find compositionShorthand notation for composition of atom

– mass# Symbol– atomic#

• 197Au• 79

Isotopes

Atoms w/ same # of p+ but different # of no

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, 2.5

2.4

Figure 2.4

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2.5

Figure 2.5

figure 02-05.jpg

Atoms: The Constituents of Matter

An atom can combine with other atoms to form molecules. Review Table 2.1

2.1

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 2.2

2.6

Figure 2.6

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2.7

Figure 2.7

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Table 2.2

Table 2.2

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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 2.3

2.8

Figure 2.8

figure 02-08.jpg

Table 2.3

Table 2.3

table 02-03.jpg

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 2.9

2.9

Figure 2.9

figure 02-09.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, 2.11

2.10

Figure 2.10

figure 02-10.jpg

2.11

Figure 2.11

figure 02-11.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 2.12

2.12

Figure 2.12

figure 02-12.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 2.13

2.13

Figure 2.13

figure 02-13.jpg

Water: Structure and Properties

Water’s molecular structure and capacity to form hydrogen bonds give it unusual properties significant for life. Review Figure 2.15

2.15

Figure 2.15

figure 02-15.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 2.18

2.18

Figure 2.18

figure 02-18.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 2.19

2.19

Figure 2.19

figure 02-19.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

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 2.21

2.21

Figure 2.21

figure 02-21.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 Biology6th ed

William K Purves, David Sadava, Gordon H Orians, H Craig Heller, Sinauer Associates, Inc., 2001