The Chemical Context of Life Chapter 2 Notes The Chemical Context of Life

Concept 2.1 Organisms are composed of __________: anything that takes up space or has mass ___________: a substance that cannot be broken down by chemical reactions ___________: substance consisting of two or more elements in a fixed ratio

Concept 2.1 Life requires about 25 elements 4 of those make up 96% of living matter _______________________________________________________ Trace Elements are those that are required in only minute quantities -ex. Iron, iodine

Concept 2.1

Concept 2.2 _________: smallest unit of matter that still retains the properties of an element ___________________: Protons (+), Neutrons (0), Electrons (-) Protons and Neutrons have a mass of 1 dalton. Electrons have no mass

Concept 2.2 ___________________: # of protons _______________: sum of protons + neutrons __________________: different atomic forms of an element. -ex. Carbon-12 (99%), Carbon-13 (1%), Carbon-14 (<1%)

Concept 2.2 C-12 and C-13 are stable. C-14 is unstable, and radioactive. It will decay giving off particles and energy. Carbon-14 will decay into Nitrogen

Concept 2.2 An atom’s electrons vary in the amount of energy they possess. ____________: the ability to do work. _______________: energy that matter stores because of its position or location Electrons have potential energy because of their position in relation to the nucleus.

Concept 2.2 (a) A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons Third shell (highest energy level) Second shell (higher energy level) Energy absorbed First shell (lowest energy Atomic nucleus lost

Concept 2.2 The different states of potential energy that electrons have in an atom are called energy levels or electron shells. - the first shell has the lowest energy. The second shell has more than the first, etc. __________________: those in the outermost shell

Concept 2.2 1H 2He 3Li 4Be 5B 6C 7N 8O 9F 10Ne 11Na 12Mg 13Al 14Si 15P Hydrogen 1H 2 Atomic number Helium 2He He Atomic mass 4.00 First shell Element symbol Electron- distribution diagram Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Nitrogen 7N Oxygen 8O Fluorine 9F Neon 10Ne Second shell Sodium 11Na Magnesium 12Mg Aluminum 13Al Silicon 14Si Phosphorus 15P Sulfur 16S Chlorine 17Cl Argon 18Ar Third shell

Concept 2.3 Atoms will bond with others to gain stability ________________: sharing of a pair of valence e- by two atoms -ex. Hydrogen atoms will share their electrons. They become H-H

Concept 2.3

Concept 2.3 __________________: the attraction of an atom for the electrons of a covalent bond ____________________: when the electrons are shared equally ____________: when one atom is bonded to a more electronegative atom

Concept 2.3  – + H O H2O

Atoms and Molecules _____________: when two atoms are so unequal in their attraction for electrons that one atom will strip the electrons from its partner _________: a charged atom; cation has a positive charge, anion has a negative charge (ca+ion; a negative ion) Compounds formed by ionic bonds are salts

Concept 2.3 Na Cl Na Cl Na Cl Na+ Cl– Sodium atom Chlorine atom Sodium ion (a cation) Chloride ion (an anion) Sodium chloride (NaCl)

Atoms and Molecules The advantage of weak bonding is that the contact can be brief _______________: H is covalently bonded to an electronegative atom and attracted to another electronegative atom. -ex. Water and ammonia

Concept 2.3   + Water (H2O) Ammonia (NH3) Hydrogen bond

Atoms and Molecules ________________: making and breaking of chemical bonds. - starting material is reactants - ending material is products __________________: point at which reactions offset one another.

Atoms and Molecules