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 elements4 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 NitrogenRadioisotopes 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.

(a) A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons

Third shell (highest energylevel)

Second shell (higherenergy level)

Energyabsorbed

First shell (lowest energylevel)

Atomicnucleus

Energylost

Potential Energy

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

Lithium

3LiBeryllium

4BeBoron

5BCarbon

6CNitrogen

7NOxygen

8O

Fluorine

9FNeon

10Ne

Helium

2HeAtomic number

Element symbol

Electron-distributiondiagram

Atomic mass

2He

4.00Firstshell

Secondshell

Thirdshell

Sodium

11NaMagnesium

12Mg

Aluminum

13AlSilicon

14SiPhosphorus

15PSulfur

16S

Chlorine

17ClArgon

18Ar

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

Chemical Bonds

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 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

NaSodium atom Chlorine atom

Cl Na+

Sodium ion(a cation)

Cl–Chloride ion

(an anion)

Sodium chloride (NaCl)

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

Weak bonding

Hydrogen Bonding +

+

+

+

+

Water (H2O)

Ammonia (NH3)

Hydrogen bond

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

Weak bonding

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 concentrationAffected by concentration of

reactants or products

Atoms and Molecules