Introduction to Chemistry Chapter 2

Introduction Matter - anything that has mass Made of elements (92 naturally occurring Element - substance that cannot be broken down to other substances by chemical reactions Elements consist of small units - atoms Atom – the smallest unit of matter that is unique to a particular element Each element has a chemical symbol 1 st 1 or 2 letters of its English or Latin name Eg. Hydrogen – H, silicon – Si To represent 1 atom of an element – simply write its appropriate symbol. Eg. H = 1 atom of hydrogen

Atomic Structure Atoms of all elements contain subatomic particles 3 kinds Protons Neutrons Electrons

Atomic Structure

Protons Found in the nucleus Carry a positive charge Number of protons = number of electrons (usually) Numbers do not vary Numbers are specific for each element Eg. H = 1, He = 2, C = 6

Atomic Structure Neutrons Found in the nucleus Electrically neutral Numbers can vary Isotope – an atom that has a different number of neutrons in its nucleus than other atoms of the same element Radioactive isotope – decays spontaneously which leads to a change in protons = a different element

A Typical Hydrogen Atom

Deuterium, An Isotope of Hydrogen

Tritium, an Isotope of Hydrogen

Atomic Structure Electrons Orbit the nucleus Carry a negative charge Number of electrons = number of protons (usually) Numbers can vary Ion – an atom or group of atoms that has gained or lost 1 or more electrons

Summary of Atomic Structure

Chemical Bonding Most atoms are able to attach to other atoms by specific bonding forces = chemical bonds Molecule – 2 or more atoms bonded together Element – atoms are the same kind Compound – atoms are different Chemical formula represents kinds and numbers of molecules Structural formula shows the location of the bond Indicated by a dash between appropriate atoms Atoms of each element will form a specific number of bonds

Chemical Bonding

Chemical Properties Determined by: Arrangement of atoms Numbers of atoms Types of atoms Eg. Sugar = C 6 H 12 O 6

Acids and Bases Acid – a substance that, when put into water, gives up H + Donates H + to a solution Base – a substance that, when put into water, gives up ions that will combine with H + Takes H + out of solution pH scale Ranges from 0 – 14. pH of human blood = 7.4 Maintained by a buffer system Resists change in pH

The pH Scale

Chemical Organization Four of the most widely distributed elements on earth are: Oxygen, carbon, hydrogen, nitrogen 95% of the weight of cellular animal matter 2 major classes of compounds Inorganic compounds are missing C or H Organic compounds are compounds of carbon Principle bonds: C – C and C – H

Carbon Carbon is unusual Atoms of most elements can bond to like atoms Number of atoms so bondable is usually limited Carbon atom – much more versatile Can form as may as 4 bonds with other atoms, including other C atoms More or less long chains of carbon atoms can form this way C atoms can be joined into rings and other shapes C – C combinations introduce tremendous complexity and variety into molecular structure

Categories of Organic Compounds Four categories form the basis of living matter and are found in all types of cells. Carbohydrates Sugars and starches Lipids Fats Proteins Nucleic acids DNA, RNA

Carbohydrates Contain C, H, O Types Monosaccharides – simple sugars Disaccharides – 2 simple sugars bonded together = a double sugar Form a larger molecule Polysaccharides – many sugars bonded together Eg. Starches

Carbohydrate Structure

Functions of Carbohydrates Function in 2 capacities Structural building blocks of cellular substances A source of energy

Lipids Fats and their derivatives Contain C, H, O Structure consists of a glycerol and 3 fatty acid chains (C atom chains) Chains are of varying length Triglyceride (a fat molecule) 3 molecules of fatty acids 1 molecule of glycerol

Lipid Structure

Functions of Lipids Food Storage Main function Structural component of cells Rich source of cellular energy

Saturated vs. Unsaturated Fats Unsaturated fat Carbons in the fatty acid chains are double bonded, H is not bonded to them. Polyunsaturated = many double bonds Many carbon atoms without H attached Saturated fat All carbon atoms have hydrogen bonded to them

Proteins Structure consists of molecules of amino acids bonded together to form long chains Contain C, H, O, N, sometimes S General structure of an amino acid Amine group (NH 2 ) Carboxyl group (COOH) R group Varies in structure Animal cells usually contain 23 types of amino acids

Amino Acid Structure

Protein Molecules

Variations in Protein Structure 100’s of a.a. units may be joined together in a single protein molecule Structurally can vary in almost unlimited fashion Possible for no 2 organisms to have exactly the same types of proteins The difference in life between organisms is the arrangement of amino acids Proteins are very specific for each organism

Functions of Proteins Food source ( to some extent) 2 more important roles Construction materials (building blocks) out of which the basic framework of cells is built Enzymes Catalyst Speed up specific chemical reactions Structure is not changed Can be used again

Enzyme Chemistry

Nucleotides Contain C, H, O, N, P Consist of 3 units Phosphate group - P 5-C sugar Ribose Deoxyribose Nitrogen base One of a series of compounds that contain N as well as C Function as energy carriers (ATP) and genetic systems (DNA)

Energy carriers Nucleotides have the property of being able to link up with 1 or 2 additional phosphate groups Phosphate bonds of ADP and ATP are high energy bonds Energy that is required to form the bonds is derived in cells from a process called cellular respiration. ATP is the significant energy rich end product of respiration

Genetic systems Nucleic acids - many nucleotides Extended chains of up to 1000’s of nucleotide units 2 types Ribonucleic acids (RNA) – a single chain consisting of ribose nucleotides Deoxyribonucleic acid (DNA) – a double chain consisting of deoxyribose nucleotides Bonding Sugar component of l nucleotide bonds to the phosphate component of the next nucleotide Form an extended molecular thread from which N- bases project as side chains

Nitrogen bases RNA – 4 possible Adenine - A Cytosine - C Guanine - G Uracil – U DNA – 4 possible Adenine – A Cytosine – C Guanine – G Thymine - T

Functions of Nucleic Acids DNA – stores information that controls all cell activities Tells the cell how to construct protein molecules RNA – helps construct the proteins

Nucleic Acid Structure

Sample Exam Questions A substance that cannot be broken down to other substances by chemical reactions is a (an) A. Atom B. Molecule C. Element D. Compound The two strands of DNA are held together by A. Bonds between nitrogen bases B. Bonds between sugar and phosphate molecules C. Bonds between amino acids D. Bonds between lipids