Chapter 2 The Basics of Life

Matter, Energy, and Life Matter: Anything that has mass and occupies space. Energy: The ability to do work. Two types of energy: Kinetic energy - Energy of motion Potential energy - Stored energy, available to do work

Law of Conservation of Energy AKA The First Law of Thermodynamics Energy is never created or destroyed. Energy can be converted from one form to another, but the total energy remains constant.

Forms of Energy There are five forms of energy: Mechanical energy – Movement Nuclear energy – Atomic reactions Electrical energy – Flow of charged particles Radiant energy – Heat, light, x-rays and microwaves Chemical energy - Energy in chemical bonds

What is the nature of matter? Matter is made up of atoms & elements. Atoms are the smallest unit of matter that exists alone & made up of: Protons Electrons Neutrons Elements are chemical substances made up of 1 kind of atom. The Periodic Table (CP – p.1065, H – Back of book)

The Periodic Table of the Elements Mass or weight The Periodic Table of the Elements

Atomic Structure Atoms are composed of: Protons – “+” charged Neutrons – no charge Electrons – “-” charge

Atomic Structure

Elements Elements are chemical substances made up of one kind of atom. Isotopes Atoms of the same element that have different numbers of neutrons. Atomic weight is isotope average in a mixture. Mass number The sum of protons and neutrons in the nucleus.

Isotopes of Hydrogen

Electrons Electrons occupy specific energy levels around the nucleus. Energy levels hold specific numbers of electrons. The first energy level can have up to 2 electrons. Atoms seek to have a full outer energy level. Atoms that have full outer energy levels are inert. Other atoms seek to fill their outer energy levels through chemical bonds.

The Formation of Molecules Molecules consist of two or more atoms joined by a chemical bond. A compound is a chemical substance made of two or more elements combined in chemical bonds. The formula of a compound describes the nature and proportions of the elements that comprise the compound. H2O

Molecules and Kinetic Energy Molecules are constantly in motion. Temperature is a measure of the average speed of the molecules in a substance. The greater the speed, the higher the temperature. Measured in Fahrenheit, Celsius or Kelvin Heat is a measure of the total kinetic energy of molecules. Measured in calories (amount of heat that will raise 1g of water 1 degree Celsius). Heat and Temperature are related. Add heat energy to a substance and the molecules will speed up, and the temperature will rise.

Ionic Bonds The attraction of oppositely charged ions. Ions are atoms that gain or lose electron(s). Cation - When an atom gives away an electron, therefore has a positive charge. (Na+) Anion - When an atom accepts an electron, therefore, has a net negative charge. (Cl-)

Ionic Bonds When atoms gain or lose electrons, they become ions. Two oppositely-charged ions attract each other and form an ionic bond. Ions, due to their charge, dissolve readily in polar solvents. 15

Covalent Bonds Form by sharing electrons. The sharing of electrons cause the outer energy levels to overlap. Single, double & triple covalent bonds occur in nature.

Covalent Bonds

Hydrogen Bonds The positive hydrogen end of one polar molecule is attracted to the negative end of another polar molecule. This attraction is a hydrogen bond. Hydrogen bonds hold molecules together. Since they do not hold atoms together, they are not considered true chemical bonds. Hydrogen bonds are very important in biology. They stabilize the structure of DNA and proteins. Water molecules can “stick” together with hydrogen bonds.

Water: The Essence of Life H2O has special properties that make it an essential molecule for life. This is a polar covalent bond. - Notice how the “+” charge is located at the H end. - Why do you suppose that is? - Because the H electrons are pulled to the O and are ‘trapped’ in O’s orbit, keeping them to the inside of the molecule.

Acids, Bases and Salts Acid - Ionic compounds that release hydrogen ions (H+) into a solution. A hydrogen atom without its electron is a proton. Base - Ionic compounds that remove hydrogen ions from solution. The hydroxide ion (OH-) being negatively charged, removes positively charged H+ from solution. Salt - Ionic compounds that do not release either H+ or OH- when dissolved in water. However, they are generally the result of the reaction between an acid & a base in solution.

pH A measure of hydrogen ion concentration Solutions with high hydrogen ion concentrations Have low pH Are acidic Solutions with low hydrogen ion concentrations Have a high pH Are basic There is a 10-fold difference in hydrogen ion concentration between solutions that differ by one pH unit. A solution with pH 4 has ten times as many hydrogen ions as a solution with pH 5.

The pH Scale A measure of hydrogen ion concentration A solution with pH 4 has ten times as many hydrogen ions as a solution with pH 5.