Chapter 2 Chemistry

2.1 Atoms Matter-any substance that has mass and occupies space Atom-smallest unit of matter Atoms are composed of three subatomic particles: Electrons (-) located in energy levels or cloud outside nucleus (discovered by Niels Bohr) Protons (+) located in the nucleus Neutrons (no charge) located in the nucleus

2.1 cont’d Atomic mass-equal to the sum of the protons + neutrons and measure in Daltons (very small)- it takes 602 million million billion Daltons (6.02 x 1023) to make 1 gram. Elements-substance composed of all the same type of atom. Isotope-atoms of the same element that have a different number of neutrons. Radioactive isotopes-unstable-emit energy; posses a half life; C14 has a half life of 5600 years Electrons determine the chemical behavior of an atom. Electrons can be lost, gained or shared.

2.2 Elements Found in Living Things Periodic table-structured based on the interactions of the electrons in the outermost energy levels (valence electrons) Octet Rule-atoms try to establish eight electrons in the outermost energy level There are 92 naturally occurring elements 11 are found in organisms in more than trace amounts: H2, Na, Mg, K, Ca, C, N2, O2, P, S, Cl2 Molecules-atoms held together by energy in a stable association Compound-atoms of more that one kind of element in definite proportions. Ex: H2O

2.3 The Nature of Chemical Bonds When there is a loss of electrons, atom is oxidized; when there is a gain of electrons, atom is reduced. These reactions are called redox reactions. When electrons do not equal protons, the atom is called an ion. Cations-more protons than electrons; carries a (+) charge Anion-more electrons that protons; carries a (-) charge

2.3 Chemical bonds Ionic bonds-formed when atoms with opposite charges attract Covalent bonds-formed when atoms share electrons; can be single, double or triple

2.3 cont’d Chemical reactions-breaking and formation of chemical bonds A-B + C-D  A-C + B-D reactants products Chemical reactions are influenced by: Temperature Concentration of reactants and products Catalysts

2.4 Water Water is known as a polar molecule; it exhibits a charge separation because of its magnet-like poles. Stable, octet rule is satisfied, carries no net charge Properties: Cohesion-water “sticks to itself” Adhesion-other molecules attract to H2O Surface tension-due to cohesion

2.5 Properties of Water Specific heat-amount of heat that must be absorbed or lost by 1 gram of a substance to change its temperature 1oC. Water has a high specific heat because of its polarity Heat of vaporization-water evaporated slowly because of the numerous hydrogen bonds that must be broken Solvent-water can dissolve almost any other substance, making it a very powerful solvent Water does not associate with nonpolar molecules (hydrophobic) Water does associate with polar molecules (hydrophilic) When water is put with nonpolar molecules, these molecules are forced to assume particular shapes….this is known as hydrophobic exclusion

2.6 Acids and Bases Ionization- H2O  H+ + OH- Molar concentration of pure water is 10-7 mole/L; pH = 7 Acids-any substance that dissociates in H2O to increase [H+]; pH lower than 7 Bases-any substance that combines H+ ions when dissolved in H2O. By combining H+ ions, pH goes up; pH is higher than 7 Buffers-substances that donate H+ ions when concentration falls and takes H+ ions when concentration rises. Ex: human blood H2O + CO2  H2CO3  HCO3- + H+