2.1 Section Objectives – page 35 Review elements, bonding, properties of water, and the importance of Carbon in living things. (In order to prepare for comparing the structure and function of bio-molecules) Can be found in the book: Starr Taggart: Pg. 22-37 Principles of Life: Pg. 17-22 2.1 Section Objectives – page 35

Section 6.1 Summary – pages 141-151 ELEMENTS Matter – anything that has mass and occupies space (abiotic or biotic) – is made of substances called elements. An element is a pure substance made only of one kind of atom. (it cannot be broken down into a simpler chemical substance) Elements differ in the number of protons (positively charged particles in it’s nucleus) Section 6.1 Summary – pages 141-151

These four elements are major components of ALL LIVING THINGS. IMPORTANCE IN BIOLOGY!?!?! These four elements are major components of ALL LIVING THINGS.

Section 6.1 Summary – pages 141-151 ATOMS An atom is the smallest particle of an element that has the characteristics of that element. Atoms are the basic building blocks of all matter. Section 6.1 Summary – pages 141-151

Section 6.1 Summary – pages 141-151 ATOMS The center of an atom is called the nucleus. All nuclei contain positively charged particles called protons (p+). Most contain particles that have no charge, called neutrons (n0). Section 6.1 Summary – pages 141-151

Section 6.1 Summary – pages 141-151 There is a region of space that surrounds the nucleus called the electron cloud. In the electron cloud there are extremely small, negatively charged particles called electrons (e-) Section 6.1 Summary – pages 141-151

Section 6.1 Summary – pages 141-151 ATOMS Nucleus 8 protons (p+) 8 neutrons (n0) Electrons exist around the nucleus in regions known as energy levels. Oxygen atom The first energy level holds 2 electrons. The second and subsequent levels holds up to 8 electrons. Animated Supplemental Tutorial Section 6.1 Summary – pages 141-151

Atoms can join together during chemical bonding to form compounds A Compound is a substance made of the joined atoms of two or more different elements Compounds are represented by a chemical formula that shows the proportions of each element in the compound

Section 6.1 Summary – pages 141-151 ATOMIC BONDS Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms. For many elements, an atom becomes stable when its outermost energy level is full. Section 6.1 Summary – pages 141-151

Section 6.1 Summary – pages 141-151 ATOMS The electrons that are in the outer most energy level for that atom are called valence electrons. Section 6.1 Summary – pages 141-151

Covalent bonds (co = together, valence= outer electrons) Covalent bonds occur when two or more atoms share electrons Sharing the electrons satisfies the outermost energy level for both atoms A compound made with covalent bonds is called a molecule

Summary Section 2 – pages 152-156 Sometimes, when atoms form covalent bonds they do not share the electrons equally. This is called a polar bond. • One side of the molecule becomes positively charged… while the other side is negatively charged. Summary Section 2 – pages 152-156

Summary Section 2 – pages 152-156 Water is a Polar Molecule ***Know why the Oxygen side is negatively charged and the Hydrogen ends are positively charged. Water is an example of a polar molecule. Summary Section 2 – pages 152-156

Hydrogen bonds also found between nitrogenous bases in DNA Hydrogen bonds are a weak chemical attractions between polar molecules that involve hydrogen atoms Water molecules are attracted to each other by hydrogen bonds Hydrogen bonds also found between nitrogenous bases in DNA

Ionic bonds An ion is an atom that has gained or lost an electron. Ions have a charge due to the unequal number of protons and electrons The attractive force between two ions of opposite charge is known as an ionic bond.

Section 6.1 Summary – pages 141-151 CHEMICAL REACTIONS Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances. Anabolic Reaction Reactants Products Catabolic Reaction Reactants Products Section 6.1 Summary – pages 141-151

Section 6.1 Summary – pages 141-151 CHEMICAL REACTIONS All of the chemical reactions (breaking down OR putting together) that occur within an organism are referred to as that organism’s metabolism. Section 6.1 Summary – pages 141-151

Sodium Chlorine Sodium Chloride

6.3 Section Summary 6.3 – pages 157-163 Importance of Carbon It is as difficult to imagine life without carbon, as it is life without water. Although a cell is mostly water, most of the rest of it consists of carbon-based molecules. 6.3 Section Summary 6.3 – pages 157-163

6.3 Section Summary 6.3 – pages 157-163 Importance of Carbon Proteins, DNA, carbohydrates, and other molecules that distinguish biotic matter from abiotic are composed of carbon atoms bonded to one another and to atoms of other elements. 6.3 Section Summary 6.3 – pages 157-163

6.3 Section Summary 6.3 – pages 157-163 Importance of Carbon The study of carbon compounds is called organic chemistry. The term “organic” is used to describe molecules that have carbon skeletons (backbones of carbon….also containing hydrogen). 6.3 Section Summary 6.3 – pages 157-163

6.3 Section Summary 6.3 – pages 157-163 Importance of Carbon The word “organic” is derived from the ability of living organisms to synthesize and use these molecules. Inorganic molecules include molecules that do not contain carbon, such as water. 6.3 Section Summary 6.3 – pages 157-163

6.3 Section Summary 6.3 – pages 157-163 Importance of Carbon Carbon is very versatile. There are 4 valence electrons in a shell that holds 8 In order for it to become stable, it must form 4 covalent bonds to fill the outer shell. 6.3 Section Summary 6.3 – pages 157-163

6.3 Section Summary 6.3 – pages 157-163 Carbon Skeletons Because carbon can use one or more of its bonds to attach to other carbon atoms, it can construct endless diversity of carbon skeletons, varying in size and branching pattern. 6.3 Section Summary 6.3 – pages 157-163

6.3 Section Summary 6.3 – pages 157-163 Carbon Skeletons They can form straight chains, branched chains, or rings. 6.3 Section Summary 6.3 – pages 157-163

6.3 Section Summary 6.3 – pages 157-163 Carbon Skeletons Isomers are compounds that are made of the same elements and have the same chemical formula, but because they are in a different order and shape, they have different properties. 6.3 Section Summary 6.3 – pages 157-163

Summary Section 2 – pages 152-156 The Importance of Water Water is perhaps the most important compound in living organisms. Water makes up 70 to 95 percent of most organisms. Summary Section 2 – pages 152-156

Review: Remember Ions An atom (or group of atoms) that gains or loses electrons has an electrical charge and is called an ion.

Water is Polar Polar water molecules attract ions as well as other polar molecules. Because of this attraction, water can dissolve many ionic compounds, such as salt, and many other polar molecules, such as sugar. There is no “universal solvent”, but it is close…

Summary Section 2 – pages 152-156 Water is Polar Water molecules also attract other water molecules. Hydrogen bonds weak bonds formed between water molecules. The positive ends are attracted to the negative ends. Summary Section 2 – pages 152-156

Summary Section 2 – pages 152-156 Water is Polar Water molecules stick together due to the hydrogen bonds, But since hydrogen bonds are weak, the bond only lasts a few trillionths of a second… And then they quickly bond with other water molecules around them The tendency of molecules to stick together, called cohesion, is much stronger in water than other liquids Summary Section 2 – pages 152-156

Summary Section 2 – pages 152-156 Cohesion of Water Hydrogen bonds also give water unusually high surface tension, making it behave as though it were coated with an invisible film. Surface tension is a measure of how difficult it is to stretch or break the surface of a liquid. Summary Section 2 – pages 152-156

Summary Section 2 – pages 152-156 Cohesion of Water Adhesion is when water molecules stick to other surfaces. Because of adhesion, water is able to creep up thin tubes. How is this property important for organisms? Summary Section 2 – pages 152-156

Summary Section 2 – pages 152-156 Water Resists Temperature Change Water resists changes in temperature. Therefore, water requires more heat to increase its temperature than do most other common liquids. Summary Section 2 – pages 152-156

Summary Section 2 – pages 152-156 Water expands when it freezes Water is one of the few substances that expands when it freezes. Liquid Water Ice is less dense than liquid water so it floats as it forms in a body of water. Solid Water Gas Water Summary Section 2 – pages 152-156