essential chemistry for biology chapter 2. why chemistry?? chemicals make up everything! body...
TRANSCRIPT
Basic Chemistry
Matter Anything that takes up
space and has mass Can exist as a liquid,
solid, or gas Made up of atoms
Elements Basic building block of
matter 92 naturally occurring
elements
Basic Chemistry
Only 6 elements that make up most of the body weight of organisms C CarbonH HydrogenN NitrogenO OxygenP PhosphorusS Sulfur
Each Element Consists of ONE Kind of Atom
Smallest unit that retains the properties of a given element And to enter a chemical reaction
Composed of subatomic particles: Protons (p+) Neutrons Electrons (e-)
Move @ atomic nucleus Usually (e-) = (p+)
Electrically neutral
Atomic Symbol
Atomic Mass = Number of Protons + Number of Neutrons
Atomic Number = The Number of Protons in the Nucleus
Why are electrons so important??
determine the chemical behavior of atoms Part of atom that comes close enough for
interactions associated with energy
the field of energy around an atom is arranged as levels called electron shells
Electron Shells
have specific numbers of orbitals that may be filled with electrons atoms that have incomplete
electron orbitals tend to be more reactive
atoms will lose, gain, or share electrons in order to fill completely their outermost electron shell
these actions are the basis of chemical bonding
Molecules and Compounds
Molecules Chemical bonding that joins atoms Some contain atoms of only one element
N2
Compounds Atoms of two or more different elements
H2O Mixture
Two or more molecules mingling together
Chemical Bonds
Atoms are held together by bonds 3 main types:
Ionic bond Accept or donate electrons
Covalent bond Share one or more electrons
Hydrogen bond
Ionic Bond
Atoms gain and lose electrons Balance between protons
and electrons shifts Become “ionized”
Ion Atom that has a charge Losing an electron results
in a net positive Gaining an electron results
in a net negative charge Ionic bond
Association of two ions that have opposing charges
Covalent Bond
Covalent bond Stable and stronger
than ionic bonds Atoms share
electrons Each atom will
have a completed outer shell
Bond Notation Single covalent
bonds are written as H-H
Double covalent bonds are written as O=O
A covalent bond can be nonpolar or polar
Nonpolar covalent bond Sharing of electrons
between atoms is fairly equal
Polar covalent bond Unequal sharing of
electrons
Hydrogen Bond
Hydrogen bond Weak attraction
Form and break easily
Occurs between polar molecules
Polar bonds have charges on either end and often attract to each other
Chemical Reactions
Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones
Reactants Starting materials
Products End materials
Chemical reactions cannot create or destroy matter, They only rearrange it
Hydrogen Bonds Give Water Unique Properties
Heat Storage water temperature changes slowly and holds
temperature well Ice Formation
few hydrogen bonds break at low temperatures water becomes less dense as it freezes because
hydrogen bonds stabilize and hold water molecules farther apart
High Heat of Vaporization at high temperatures, hydrogen bonds can be
broken water requires tremendous energy to vaporize because
of all the hydrogen bonds that must be broken
Hydrogen Bonds Give Water Unique Properties
Water molecules are sticky cohesion – when one water
molecule is attracted to another water molecule
adhesion – when polar molecules other than water stick to a water molecule
Hydrogen Bonds Give Water Unique Properties
Water dissolves other polar substances
Solvent Ions and polar molecules
easily dissolve in it Solute
A dissolved substance Hydrophilic
water-loving molecules form hydrogen bonds with
water Hydrophobic
water-fearing molecules do not form hydrogen
bonds with water
Acids and Bases
When water ionizes, it releases an equal number of hydrogen ions (H+) and hydroxide ions (OH-)
Some substances release more or fewer or each Acids - Excess hydrogen ions Bases - Excess hydroxide ions
Acidic and Basic Solutions
Acidic Solutions Sharp, sour taste Molecules that
dissociate in water Release
hydrogen ions (H+)
Basic Solutions Bitter taste Molecules that
either take up hydrogen ions (H+) or release hydroxide ions (OH-)
pH Scale
The pH Scale Ranges from 0 - 14
pH below 7 is acidic [H+] > [OH-]pH above 7 is alkaline [OH-] > [H+]pH of 7 is neutral [H+] = [OH-]
Buffer Chemical or combination of chemicals that
keeps pH within normal limits
Water Ionizes
The amount of ionized hydrogen from water in a solution can be measured as pH
The pH scale is logarithmic, which means that a pH scale difference of 1 unit actually represents a 10-fold change in hydrogen ion concentration
pH = -log[H+]