2.4 Chemical reactions and enzymes The Chemistry of Life 2.1 The Nature of Matter 2.2 Properties of Water 2.3 Carbon Compounds 2.4 Chemical reactions and enzymes

Atoms Building blocks of life - the basic unit of matter Name comes from greek term – atomos – unable to be cut Very very small – 100million = 1cm Made of three subatomic particles – protons, neutrons and electrons

Subatomic particles Protons and Neutrons - the same mass Protons have a positive charge Neutrons carry no charge at all Strong forces bind protons and neutrons to form a nucleus Electrons – negatively charged particles 1/1840 mass of a proton Equal number of protons and electrons = neutral charge

Elements

Elements Pure substance – consists of only one type of atom More than 100, but less than 20 are common Number of protons –atomic number Atomic number of carbon – 6 Each carbon atom has 6 protons and therefore 6 electrons Numbers of neutrons in an element can vary

Isotopes All carbon isotopes have 6 protons Number of neutrons can vary 6, 7, 8 There are different isotopes of carbon Total number of protons and neutrons = mass number Mass number is used to identify different isotopes Atomic mass - weighted average of different isotopes

Calculating weighted average Weighed average atomic mass = sum of (atomic mass X modal abundance) for each isotope of carbon Because all isotopes have the same number of electrons, all isotopes have the same chemical properties Mass number exact weight (amu) percent abundance 12 12.000000 98.90 13 13.003355 1.10 Answer =(12 x 0.9890) + (13.003355 x 0.011) = 12.011 amu

Radioactive isotopes When the nuclei of an isotopes is unstable, it is radioactive This means the nuclei will “break down” at a constant rate over time Radiation can be dangerous, but also very useful Can be used to date the age of rock Can be used to treat cancer Kill bacteria in food Use a tracer to follow movements of substances in organisms

Chemical compounds Most elements are found combined with other elements Chemical compound - combination of two or more elements in definite proportions We write a chemical formula in a kind of shorthand Eg. H2O Water contains one hydrogen and two oxygen atoms

Chemical bonds Electrons in the outer shell dictate what kind of chemical bonds atoms can form These electrons are called valence electrons

Ionic bonds Where one or more electrons are transferred from one atom to another This distorts the neutral charge of atoms Positive and negative ions generated Positive and negative ions are attracted to each other A strong bond is formed Common with extreme ends of the periodic table

Salt formation

Covalent bonds Sometime electrons can be shared Moving electrons travel around the nuclei of both atoms The basis for a covalent bond Possibility for single, double or triple bonds Resultant structure called a molecule

Van der Waals forces Sharing can sometimes be a bit one sided Some elements have a stronger ability to attract electrons than others Even when equal, the rapid movement of electrons can can create regions that have positive and negative charges Results in a slight attraction between these areas Not as powerful as ionic bonds! But can hold molecules together