Chapter 2 Notes

The Chemical Context of Life

Concept 2.1Organisms 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 2.1Life 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

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 2.2C-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 2.2An 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

Concept 2.2

Concept 2.2The 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 2.2Hydrogen

1H

Lithium3Li

Beryllium4Be

Boron5B

Carbon6C

Nitrogen7N

Oxygen8O

Fluorine9F

Neon10Ne

Helium2He

Atomic number

Element symbolElectron-distributiondiagram

Atomic mass

2He

4.00Firstshell

Secondshell

Thirdshell

Sodium11Na

Magnesium12Mg

Aluminum13Al

Silicon14Si

Phosphorus15P

Sulfur16S

Chlorine17Cl

Argon18Ar

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

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 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

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

Atoms and Molecules

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