Chemistry notes

The following texts are the property of their respective authors and we thank them for giving us the opportunity to share for free to students, teachers and users of the Web their texts will used only for illustrative educational and scientific purposes only.

The information of medicine and health contained in the site are of a general nature and purpose which is purely informative and for this reason may not replace in any case, the council of a doctor or a qualified entity legally to the profession.

Chemistry notes

Chemistry

MATTER anything that takes up space and has mass

Made of ELEMENTS -can’t be broken down to other substances by chemical reactions
• 92 naturally occurring elements
      • Each has a unique symbol (usually first one or two letters of name)

• Some symbols dervived from Latin   EX: Sodium = Na (from Latin natrium)

• 25 chemical elements are essential to life.

• Four elements—carbon (C), oxygen (O), hydrogen (H), and nitrogen (N) = 96% of living matter
• Other 4% of organism’s weight = phosphorus (P), sulfur (S), calcium (Ca), and potassium (K)

• TRACE elements =required in minute quantities

• Some required by all organisms EX: iron (Fe)
• Others only required by some species
EX: humans need 0.15 mg Iodine (I) daily for normal thyroid gland function

ATOMS made of SUBATOMIC PARTICLES
Each kind of atom has a specific number of protons, neutrons, and electrons

SUBATOMIC PARTICLE	Electric charge	Mass	Location
Proton	+	1 dalton	In nucleus
Neutron	^_	1 dalton	In nucleus
Electron	0	negligible	Orbit nucleus in energy levels

Elements in same row have same # of electrons in their outer shells

• As move from left to right, one proton & one electron are
added to preceding element

• Atoms are electrically NEUTRAL (protons =electrons)

• Atoms that have gained or lost electrons = IONS

USES OF RADIOACTIVE ISOTOPES :
Determine age of fossils (carbon dating)
Medical diagnostic and treatment procedures
Research

= number of protons

= number of protons + neutrons

ATOMIC MASS (1 dalton = 1 amu)

Elements occur in nature as a mixture of ISOTOPES
ISOTOPES = atoms with the same number of protons
but differ in number of neutrons
EX: ¹⁴C , ¹³C, and ¹²C all have 6 protons & 6 electrons,
but different numbers of neutrons
Most isotopes are stable (EX^{: 12}C and ¹³C)
but some are radioactive (¹⁴C)

ENERGY LEVELS – 3-D space where electrons are found = ORBITAL

• Level closest to nucleus = lowest energy; outer levels have more energy
1^st level- 1 orbital holds 2 electrons
2^nd level- 4 orbitals hold 8 electrons
3^rd and higher levels- hold increasing numbers of electrons

EX: Lithium (3 ELECTRONS) has two in the first shell; one in second shell
Neon (10 electrons) has two in the first shell; eight in second shell

CHEMICAL BEHAVIOR depends on number of electrons in OUTERMOST SHELL (=VALENCE electrons)
• Atoms with the same number of valence electrons have similar chemical behaviors
• Atom with a completed valence shell = nonreactive (EX: neon)
• Atoms with incomplete valence shells = chemically reactive
• Atoms can give up, accept, or share electrons in order to have a stable outer shell

ELEMENT	# of covalent bonds
Hydrogen	1
Oxygen	2
Carbon	4
Nitrogen	3
Phosphorus	5
Sulfur	2

MOLECULES= two or more atoms of SAME or DIFFERENT elements bonded together (EX: O₂)
COMPOUNDS = two or more DIFFERENT elements bonded together (EX: H₂O)

CHEMICAL FORMULA = recipe; tells which kinds of atoms and how many
EX: H₂0 = TWO Hydrogen atoms and 1 oxygen atom
*change in characteristics when elements combine = EMERGENT property

TYPES OF BONDS

1) COVALENT: share electrons
• SINGLE- share a PAIR of electrons (shown as single dash H-O-H)
• DOUBLE- share TWO PAIRS of electrons (shown as C=C)
• TRIPLE- share THREE PAIRS of electrons (shown as )

POLAR COVALENT BONDS - sharing of electrons = unequal;
seen in atoms with differences in electronegativity
one atom slightly more positive/other more negativity

NONPOLAR COVALENT BONDS- EX: methane
electron sharing is equally distributed

2) IONIC BONDS:
electrons are transferred from one atom to another (CATION =+   ANION =-)
+/- partners (IONS) are held together by attraction between opposite charges
EX: table salt (NaCl)   Sodium loses one electron; Chlorine picks up one electron

3) HYDROGEN BONDS: weak attraction between molecules or parts of same molecule
• slightly positive hydrogen atom of one molecule attracted to slightly negative atom in another
EX: water molecule- electrons spend more time orbiting oxygen than hydrogens
so oxygen becomes slightly negative and the two hydrogens become slightly positive

4) Van der Waals Interactions-
attractions between ever changing + and - “hot spots” in covalently bonded nonpolar molecules
EX: responsible for gecko’s ability to walk up a wall

* Relative strength of bonds: Covalent > Ionic > Hydrogen bond > Van der Waals forces

Individual bonds (ionic, hydrogen, van der Waals) are weak and temporary, but collectively they are strong and play important biological roles.

CHEMICAL REACTIONS- make and break chemical bonds

OXIDATION-REDUCTION:
• Oxidation = the loss of electrons (or loss of hydrogen atoms), a molecule that loses an electron is oxidized
• Reduction = the gain of electrons (or gain of hydrogen atoms), a molecule that gains an electron is reduced

• Chemical bonds are broken and reformed/atoms are rearranged.

Reactants → products

• Reactions must be “balanced” –Number and kind of atoms in reactants must = those in products

• Matter is conserved in a chemical reaction

• Chemical reactions rearrange matter; they do not create or destroy matter.

• Some chemical reactions go to completion (all the reactants are converted to products)

• Most chemical reactions = reversible (products in forward reaction become reactants in reverse reaction)

EX: 3H₂ + N₂ <=> 2NH₃
hydrogen and nitrogen combine to form ammonia, but ammonia can decompose to hydrogen and nitrogen
Initially, reactant concentrations are high, so they frequently collide to create products
As products accumulate, they collide to reform reactants
EQUILIBRIUM
• RATE of formation of products = the RATE of breakdown of products (RATE NOT CONCENTRATION)
• Products and reactants are continually being formed, but no net change in their concentrations
• Concentration of reactants and products typically NOT EQUA; concentrations stabilize at a particular ratio
MOLECULE’S BIOLOGICAL FUNCTION RELATED TO ITS 3-D SHAPE
• Molecule with 2 atoms =linear
• Water molecule is shaped like a V, two covalent bonds are spread apart at 104.5° angle
• Shape of bigger molecule determined by the positions of the electron orbitals shared by bonded atoms
• CARBON- Formation of a covalent bonds leads to hybridization of the orbitals to four new orbitals in a tetrahedral shape
• Large organic molecules contain many carbon atoms with repeating tetrahedral pattern
MOLECULES WIH SIMIALR SHAPES CAN HAVE SIMILAR FUNCTIONS
EX: morphine, heroin, and other opiate drugs = simiilar in shape so they can bind to the same receptors as natural signal
molecules called endorphins
Binding of endorphins to receptors on brain cells produces euphoria and relieves pain.
Opiates mimic these natural endorphin effects.

http://local.brookings.k12.sd.us/krscience/open/chemistryoflife.htm

Source: http://www.biologyjunction.com/chemistry%20notes%20kelly.doc

Google key word : Chemistry notes file type : doc

Author : not indicated on the source document of the above text

If you are the author of the text above and you not agree to share your knowledge for teaching, research, scholarship (for fair use as indicated in the United States copyrigh low) please send us an e-mail and we will remove your text quickly.

Chemistry notes

If you want to quickly find the pages about a particular topic as Chemistry notes use the following search engine:

Chemistry notes

Chemistry notes

Chemistry notes

Chemistry

Chemistry notes

Chemistry notes

Please visit our home page

Larapedia.com Terms of service and privacy page

Chemistry notes