CHAPTER 2. Life’s Chemical Basis. Atoms. Element- fundamental substance consisting of only one type of atom. C, N, H, O are the most commonly occurring elements in the human body.
Life’s Chemical Basis
Element- fundamental substance consisting of only one type of atom. C, N, H, O are the most commonly occurring elements in the human body.
There are 110 different elements, but only 92 naturally occurring ones. Numbers 93-110 are very unstable and degrade quickly.
numbers of protons
and electrons. When
it doesn’t it’s called
See Appendix IV in back of textbook for good periodic table.
Atomic Number- number of protons in a nucleus of an atom. This defines which element the atom is. Always the smaller number.
Mass Number- total number of protons and neutrons in the atomic nucleus. The larger number.
Mass Number =Number of protons + Number of neutrons
Symbol Protons Neutrons Mass
O 8 8 16
Ca 20 ? 40
Na ? 12 23
Cl 17 ? 35
K ? 20 39
Fe 26 30 ?
N 7 ? 14
Isotopes have different mass numbers
after 5700 yrs you have 50 grams carbon 14 and 50 grams Nitrogen 13
Decay example- The nucleus captures an electron which basically turns a proton into a neutron. Here's a diagram of electron capture with beryllium-7
Concentrations of radioactive tracer bound to monoamine oxidase B (MAO B). Red shows the highest concentration. Clearly, lower concentrations are seen in the smoker. MAO B helps regulate nerve function and blood pressure.
Holds up to 2
holds up to 8
A model atomic structure is a diagram with successively larger circles, or shells, that keep track of all electrons in the orbital at a given energy level.
Max number of electrons in each shell
Shell Number electrons
17p+ , 17e-
11p+ , 11e-
6p+ , 6e-
8p+ , 8e-
10p+ , 10e-
1p+ , 1e-
2p+ , 2e-
7p+ , 7e-
6p+ , 6e-
1p+ , 1e-
Element Valance electrons
Chemical bond – joining one atom to another by electrons joining
Compound – are molecules that consist of two or more different elements in proportions combined by a chemical bond
Molecule – two or more atoms of the same element or different elements joined by a chemical bond
Formula- the proportional arrangement and short hand for a chemical
Chemical reaction- reacting two or more compounds and or molecules with one another
Reactants – the things that are mixed together in a chemical reaction
Products – the things that are produced in a chemical reaction
Unfilled shells make atoms likely to react
Hydrogen, carbon, oxygen, and nitrogen all have vacancies in their outer shells
Bond is union between electron structures of atoms
Atoms bond to form molecules
Molecules may contain atoms of only one element - O2
Molecules of compounds contain more than one element - H2O
Use symbols for elements when writing formulas
*****(Need to remember!) Formula for glucose is C6H12O6
Chemical equation shows reaction
Reactants ---> Products
Equation for photosynthesis:
The bonding behavior of biological molecules starts with the number and arrangement of electrons in each type of atom.
Ionic, covalent, and hydrogen bonds are the main categories of bonds between atoms in biological molecules.
Atom has equal number of electrons and protons - no net charge
Atom loses electron(s), becomes positively charged ion
Atom gains electron(s), becomes negatively charged ion
One atom loses electrons, becomes positively charged ion
Another atom gains these electrons, becomes negatively charged ion
Charge difference attracts the two ions to each other
Sodium atom (Na) (+1 ion)
Outer shell has one electron
Chlorine atom (Cl) ( -1 ion)
Outer shell has seven electrons
Na transfers electron to Cl, forming Na+and Cl-
Ions remain together as NaCl (no charge)
The electron from sodium atom is lost to the chlorine atom which gains the electron.
Atoms share a pair or pairs of electrons to fill outermost shell
Example below is a single bond
Single bonds between H and carbon . Methane (lower right) has 4 single bonds formed with hydrogen.
Share 6 electrons for three bonds (triple)
Non Polar – share electrons equally
Polar – do not equally share electrons
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
Oxygen is much more electronegative than hydrogen
shared electrons spend more time with the oxygen part of the molecule than with the hydrogen part
Unequal sharing of electrons results in the oxygen having a partial negative charge and the hydrogen atoms having a partial positive charge.
Molecule has no net charge
Oxygen end has a slight negative charge
Hydrogen end has a slight positive charge
Non polar if atoms share electrons equally
Hydrogen gas (H - H)
Polar if electrons spend more time near nucleus with most protons
Electrons more attracted to O nucleus than to H nuclei
Atom in one polar covalent molecule is attracted to oppositely charged atom in another such molecule or in same molecule
Hydrogen bonds are weak.
Important role in the structure and function of biological compounds.
Found in DNA
Gives DNA unique properties
Bonds to hydrophilic substances
Repels hydrophobic ones
Expands & floats when it freezes
Capacity to dissolve substances
Evaporation – heat energy converts liquid water to a gaseous state
Form skin evaporation can help cool body
Water boils at sea level at 100C or 212F.
Water freezes at sea level at 0C or 32F.
Cohesion – has the ability to resist rupturing when placed under tension
Cohesion causes high surface tension
Shows a capacity to resist rupturing when stretched
Helps to absorb nutrient laden water to grow
Water rise in tubes
Some evaporates in leaves
Pull other water molecules to fill in behind those evaporated
This slide shows hydrogen bonding (white dotted line)
Solids are more organized in shape.
In ice, hydrogen bonds lock molecules in a lattice
Water molecules in lattice are spaced farther apart then those in liquid water
Ice is less dense than water
Hydrogen bond with water
Repelled by water
Liquid water can absorb much heat before its temperature rises
Much of the added energy disrupts hydrogen bonding rather than increasing the movement of molecules
Large energy input can cause individual molecules of water to break free into air
As molecules break free, they carry away some energy (lower temperature)
Evaporative water loss is used by mammals to lower body temperature
Ions and polar molecules dissolve easily in water
When solute dissolves, water molecules cluster around its ions or molecules and keep them separated
Hydrogen bonding holds molecules in liquid water together
Creates surface tension
Allows water to move as continuous column upward through stems of plants
Fig. 2-11a, p.27
Ions dissolved in fluids inside and outside the each living cell influence its structure and function.
Among the most influential are hydrogen ions.
They have far reaching effects largely because they are chemically active and because there are so many of them.
Measures H+ concentration of fluid
Change of 1 on scale means 10X change in H+ concentration
Highest H+ Lowest H+
Acidic Neutral Basic
Both can cause severe damage
Also called alkaline
A coal-burning power plant emits sulfur dioxide, which dissolves in water vapor to form acid rain
A salt is any substance that dissolves in water and releases ions (not H+)
Forms when and acid and a base are mixed.
HCL + NaOH H2O + NaCl
Hydrochloric acid reacting with sodium hydroxide produces water and sodium chloride (salt)
NaCl (solute) dissolves in water (solvent) forms Na+ and Cl- (ions)
When blood pH rises, carbonic acid dissociates to form bicarbonate and H+
H2C03 -----> HC03- + H+
When blood pH drops, bicarbonate binds H+ to form carbonic acid
HC03- + H+ -----> H2C03
Ions dissolved in fluids on the inside and outside of cells have key roles in cell function.
Acidic substances release hydrogen ions, and basic substances accept them.
Salts are compounds that release ions other than H+ and OH-.
Acid-base interactions help maintain pH, which is the H+ concentration in a fluid.
Buffer systems help maintain the body’s acid-base balance at levels suitable for life.