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

1st 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

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 Bonding

Chemical Properties

Determined by: Arrangement of atoms Numbers of atoms Types of atoms

Eg. Sugar = C6H12O6

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 (NH2) Carboxyl group (COOH) R group

Varies in structure

Animal cells usually contain 23 types of amino acids

Amino Acid Structure

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