Embed Size (px)
Citation preview
CHAPTER 2The Chemical Context of Life
2.1 Matter is made of elements and compounds.
Organisms are composed of matter - anything that takes up space or has mass
An element is a substance that cannot be broken down by chemical reactions.
Fe, Ca, K
A compound is a substance consisting of two or more elements in a fixed ratio.
NaCl, HCl, H2O2 , C6H12O6
Matter - elements and compounds
Life requires about 25 elements C, O, H, and N make up 96% of all living
matter S, P, Ca, and K make up the remaining 4%
Trace elements are those that are required, but only small amounts. N and I
Deficits may have severe consequences
Nitrogen deficiency - growth of plant
Iodine deficiency – enlargement of thyroid gland
Table 2.1
2.2 – An element’s properties depend on its structure
An atom is the smallest unit of matter that still retains the properties of an element. Similar to a cell being the basic unit of life
Subatomic particles help us to better understand atoms. Protons (p+) Neutrons (n0 - no charge) Electrons (e-)
2.2 Properties and Structure
Atomic number is the # of p+
In neutral (uncharged atom) also equals e-
Mass number (Atomic mass) = p+ + n0
Isotopes are the different forms of an element. # of n0 varies in the nucleus Often used as radioactive markers/tracers for
testsYou should be able to identify and determine mass
and atomic number for elements on the p-table.
2.2 – Properties and Structure
The e- of an atom have different energy – ability to do work.
e- have stored (potential)energy because of their position in relation to the nucleus. 1st shell (closest to nucleus) least energy 2nd shell more energy than 1st, etc.
Outer most shell contains valance e-
identified by group number (groups ↑↓) # of unpaired e- indicates reactivity of element
Third shell (highest energylevel)
Second shell (higherenergy level)
Energyabsorbed
First shell (lowest energylevel)
Atomicnucleus
Energylost
e- Energy Shells
Valence e- of common elements
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
2.3 Chemical Bonding
Atoms will bond with other atoms to gain stability. Stable when valence shell is full.
Covalent bonds Ionic bonds
Chemical Bonding
Covalent bonds are formed when 2 atoms share a pair or pairs of valence e-. Hydrogen (H) atoms will share their e-.
They become H-H. H2O – H covalently bonded to O
2.3
2.3 – Chemical Bonding
Electronegativity is a measure of an atoms ability to the attract the e- of another atom to form a covalent bond. Sharing of e- results in a strong bond. Two types of covalent bonds
Nonpolar Polar
Covalent bonding…
Nonpolar when the e- are shared equally results in no charge on either atom
involved
Polar when one atom is bonded to a more electronegative atom results in charge (+/-) on one atom
–
+ +
H H
O
H2O
Polarity of H2O
2.3 Chemical Bonding
Ionic bonds occur when two atoms are so unequal in their attraction for e- that one atom will strip the e- from its partner. These bonds are not as strong as covalent
bonds.
An ion is a charged atom; Cations have a “+” charge, ca+ion Anions have a “–” charge, a negative ion
Compounds formed by ionic bonds are salts.
Ionic Bonds
Na Cl Na Cl
NaSodium atom Chlorine atom
Cl Na+
Sodium ion(a cation)
Cl–Chloride ion
(an anion)
Sodium chloride (NaCl)
2.3 Chemical Bonding
The advantage of weak bonding is that the contact/bond between atoms can be brief.
Hydrogen bonds occur when H is covalently bonded to an electronegative atom and attracted to another electronegative atom. Water and ammonia Water and water Bases in DNA
Hydrogen Bonding +
+
+
+
+
Water (H2O)
Ammonia (NH3)
Hydrogen bond
Hydrogen bonding…
Hydrogen bonding…
Shape and Function
Molecules have distinct shape and size Related to atoms and bonds contained
within As mentioned before shape/structure is
directly related to function Determines how molecules interact and
respond to each other Opiates and endorphins – chemicals with
similar shapes interact with similar receptors on the brain, causing similar effects
2.4 – Reactions make or break bonds.
Chemical reactions involve breaking and making new chemical bonds. Start with reactants. End with products.
Coefficient and subscript tells you how much of each
What is the reverse reaction of photosynthesis?
Chemical Reactions
2.4 – Reactions make or break bonds.
Chemical equilibrium occurs when the forward and reverse reactions occur at the same rate. Concentrations have stabilized Concentrations are NOT equal each other
