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

What is life made of? 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

Essential Elements for Life 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

What are elements made of? _________: 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

Atomic Number and Mass ___________________: # of protons _______________: sum of protons + neutrons __________________: different forms of an element (same # of protons, more neutrons) -ex. Carbon-12 (99%), Carbon-13 (1%), Carbon-14 (<1%)

Isotopes C-12 and C-13 are stable. C-14 is unstable, and radioactive. Radioactive Isotope: atom that will decay giving off particles and energy. Carbon-14 will decay into Nitrogen Radioisotopes are useful in science and medicine

Electrons and Energy 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.

Potential Energy (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

Electron Shells 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

Electrons and Chemical Properties 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

Chemical Bonds Atoms will bond with others to gain stability (fill valence shell) ________________: sharing of a pair of valence e- by two atoms -ex. Hydrogen atoms will share their electrons. They become H-H

Covalent Bonds

Types of Covalent Bonds __________________: 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

Polar Covalent Bonds  – + H O H2O

Unequal sharing of electrons _________: a charged atom formed when two atoms are so unequal in their attraction for electrons that one atom will strip the electrons from its partner cation has a positive charge, anion has a negative charge (ca+ion; a negative ion) _________: bond formed when cations and anions attract each other Compounds formed by ionic bonds are salts

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

Weak bonding 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

Hydrogen Bonding   + Water (H2O) Ammonia (NH3) Hydrogen bond

Weak bonding Nonpolar molecules may have positively and negatively charged regions at any moment _______________: enables nonpolar molecules to attract each other May form between regions of the same protein help form shape

Molecular Shape Molecules have characteristic shape and size Shape determines how molecules recognize and respond to one another Ex: opium and endorphins

Forming and Breaking Bonds ________________: making and breaking of chemical bonds. - starting material is reactants - ending material is products All reactions are reversible

Forward and Reverse Reactions __________________: point at which reactions offset one another. No net effect on concentration Affected by concentration of reactants or products

Atoms and Molecules