Atoms
Smallest electrically neutral particle of an element that retains the properties of that
element.
John Dalton
(1766-1844) EnglishExperimental evidence
Ratios in which elements combine in chemical reactions
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.
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 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-
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
Despite this difference they are chemically alike
Same # of p+ + e-
P+ + e- are responsible for chemical behavior
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
Atoms: The Constituents of Matter
Electrons are distributed in shells of orbitals containing a maximum of two. Review Figures 2.4, 2.5
Atoms: The Constituents of Matter
An atom can combine with other atoms to form molecules. Review Table 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
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
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
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
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
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
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
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
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
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
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
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.