The Chemistry Of Life

Chemistry of Life Life depends on chemistry. When we eat food or breathe oxygen, our body uses these materials to keep us alive. Just as buildings are made from bricks, steel, glass, and wood, living things are made from chemical compounds. If the first task of an architect is to understand building materials, then the first task of a biologist is to understand the chemistry of life.

Periodic Table of the Elements

Atoms The study of chemistry begins with the basic unit of matter, the atom. The Greek word atomos, which means unable to cut was first used to refer to matter by the Greek philosopher Democritus nearly 2500 years ago. Democritus asked a question.........how small can things be broken down to???? Atoms are incredibly small: 100 million in a row = 1 cm long. Despite its extremely small size, atoms are actually made-up of three smaller parts called sub-atomic particles: Protons (+), Neutrons (o), & Electrons (-). The electron is a negatively charged particle (-) with 1/1836 the size of a proton. Electrons are in constant motion around the nucleus of atoms. They are attracted to the opposite charge of the protons in the nucleus, but remain outside due to the energy of their motion.

The Atom

Elements and isotopes A chemical element is a pure substance that consists entirely of one type of atom. Over 100 elements are known, but only about two-dozen are commonly found in living organisms. Elements are represented by 1 or 2 letters: H - hydrogen, Na – sodium The number of protons in an atom of an element is its atomic number. For example, carbon's atomic number is 6. This means that each atom of carbon has 6 protons, and consequently, 6 electrons.

Elements and isotopes (cont) Isotopes: Atoms of an element can have different numbers of neutrons. For example, some atoms of carbon have 6 neutrons, some have 7, and a few have 8. Atoms of the same element that differ in the number of neutrons they contain are known as isotopes. The sum of the protons and neutrons in the nucleus of an atom is called its mass number. BECAUSE THEY HAVE THE SAME NUMBER OF ELECTRONS, ALL ISOTOPES OF AN ELEMENT HAVE THE SAME CHEMICAL PROPERTIES. Radioactivity???

Isotopes

Chemical compound In nature, most elements are found combined with other elements in compounds. Scientist show the composition of compounds by a kind of shorthand known as a chemical formula. Water which has 2 hydrogen atoms for every 1 oxygen atom has a chemical formula of H2O. The formula for table salt is NaCl, meaning that salt has a 1:1 ratio of sodium (Na) and Chlorine (Cl). The physical and chemical properties of compounds are usually very different from the elements that formed them.

Chemical Bonds The atoms in compounds are held together by chemical bonds. Much of chemistry is devoted to understanding how and when chemical bonds form. Bond formation involves the electrons that surround each atomic nucleus. The electrons that are available to form bonds are called valence electrons. The main types of chemical bonds are ionic bonds and covalent bonds. Ionic bonds are formed when 1 or more electrons are transferred from one atom to another.

Ionic Bonds (transferred of electrons)

Chemical Bonds (cont) Sometimes electrons are shared by atoms instead of being transferred. What does it mean to share electrons? It means that the moving electrons actually travel in the orbits of both atoms. (single, double, triple bonds???) The structure that results from the joining of atoms by covalent bonds in called a molecule. The molecule is the smallest unit of most compounds. Van der Waals Forces & Gecko's grip???

Van der Waals Forces

Properties of Water Water is one of the few compounds that is liquid at the temperatures found over much of the Earth's surface. Unlike most substances, water expands as it freezes. Thus, ice is less dense than liquid water, which explains why ice floats on the surface of lakes and rivers. If ice sank to the bottom, the situation would be disastrous for fish and plant life in regions with cold winters. Like all molecules, a water molecule (H2O) is neutral. The positive charges on its 10 protons balance out the negative charges on its 10 electrons. However, there is more to the story...

Water is cohesive (sticky)

POLARITY With 8 protons in its nucleus, an oxygen atom has a much greater attraction for electrons than does the hydrogen atom with a single proton in its nucleus. Hydrogen Bonds??? 1. Water strider? 2. Double Helix?

Hydrogen Bonding

Water Strider

The End