Chemical Elements and Water

How do we organize living things? Biosphere Ecosystem Community Population Organism Organ System Organ Tissue Cell Organelle Molecule Atom

Why Chemistry? To understand the structures and functions of living organisms, it’s essential to know the basis of all living things. The properties of life emerge from the arrangement of its chemical parts into higher and higher levels of biological organization. At the base of the hierarchy of living things:  Elements, atoms, molecules

What’s the Matter? Matter  Anything that occupies space and has mass.  In forms as diverse as rock, water, air, and living organisms  Composed of chemical elements Element  A substance that cannot be broken down to other substances by ordinary chemical means.  Life requires about 25 chemical elements:  4 make up about 96% of the human body: oxygen (O), carbon (C), hydrogen (H), and nitrogen (N) Main ingredients in biological molecules such as proteins, sugars, and fats  A few others make up the remaining 4%: Calcium (Ca), phosphorous (P), sulfur (S), sodium (Na), Chlorine (Cl), and Magnesium (Mg) Important in bone formation, nerve signaling, and DNA synthesis

Subatomic Particles Atoms are dividable to 3 main subatomic particles:  Protons are positive and located in the nucleus of the atom  Neutrons are neutral and located in the nucleus  Electrons are negative and found on orbitals around the nucleus

If two atoms have different numbers of protons they are different elements – atomic number – is the number that is assigned to every element and is equal to its number of protons If two atoms have different numbers of neutrons but the same number of protons, these atoms are isotopes. Many elements have radioactive isotopes – these are isotopes that have an unstable nucleus that decays and releases energy spontaneously (radioactive radiation)

Radioactive isotopes are frequently used in biology for:  Basic research (radioactive tracers, dating fossils)  Medical diagnosis (radioactive tracers, medical imaging, radiation treatment)  Food industry (sterilizing and preserving food) Radioactive isotopes are also dangerous because they can damage DNA molecules and in high doses can cause serious burns as well.

Chemical Bonds Atoms can bind with each other to form more complex forms of matter called compounds. There are two basic types of bonds:  Covalent bond – electrons are shared between atoms  Ionic bond – electrons are lost or gained by atoms and the oppositely charged ions are held together by electrostatic attraction.

Polarity Some molecules with covalent bonds share the electrons equally or the molecule is symmetrical – nonpolar molecules (Ex. Oil) Some molecules have an uneven electron sharing. One atom attracts the electrons more in the bond than the other – polar molecules (Ex. Water)

Chemical Reactions When chemical bonds break and new ones are formed chemical reactions take place. Chemical reactions are represented by chemical equations When you write chemical equations, the reactants are always written on the left side of the equation and the products on the right side of the equation. There is a = or an between the two sides of the equation. Chemical equations must always be balanced. A chemical reaction:

Electronegativity  An atom’s attraction for its electrons, including shared electrons.  Molecules like 0 2 consist of two identical atoms, and thus exert an equal pull on the electrons.  Covalent bonds are said to be nonpolar because the electrons are shared equally between the atoms. Some compounds, like CH 4, also have nonpolar bonds.

Electronegativity and Water Electronegativity and water Unequal sharing of electrons produces what is called a polar covalent bond.  The pulling of shared electrons closer to the more electronegative atom makes that atom partially negative and the other atom partially positive.  Oxygen is one of the most electronegative elements, and thus attracts the shared electrons in H 2 O much more strongly than H does.  the O atom has a slight negative charge and each H atom a slight positive charge.  The V shape and its polar covalent bonds make water a polar molecule

Water

Hydrogen bonds Since the positively charged region in H20 is always a hydrogen atom, this polar covalent bond is called a hydrogen bond. O on each water molecule can form hydrogen bonds with two H atoms Each H 2 0 molecule can hydrogen-bond to as many as four partners. The hydrogen bond is a weak bond.

Water

Properties of Water Cohesive Thermal Solvent

Properties of Water Cohesive  Tendency of molecules to stick together  Much stronger for water than for most other liquids.  Hydrogen bonds give water unusually high surface tension, a measure of how difficult it is to stretch or break the surface of a liquid  Water looks as though it were coated with an invisible film.  Very important in the living world:  Trees depend on cohesion to help transport water and nutrients from their roots to their leaves.

Properties of Water Thermal  Because of hydrogen bonding, water has a better ability to resist temperature change than most other substances.  Because of this, Earth’s giant water supply moderates temperatures, keeping them within the limits that permit life:  When water is heated, the heat energy first disrupts hydrogen bonds and then makes water molecules move faster. Because heat is absorbed as the bonds break, water absorbs and stores a large amount of heat while warming up only a few degrees.  When water is cooled, more hydrogen bonds form. Heat energy is released when the bonds form, slowing the cooling process.

Properties of Water Thermal (continued)  A large body of water can store a huge amount of heat from the sun during warm periods.  At cooler times, heat given off from the gradually cooling water can warm the air. That’s why coastal areas generally have milder climates than inland regions. Water’s resistance to temp. change also stabilizes ocean temperatures, creating a favorable environment for marine life.  And at 66% of your body weight, water helps moderate your internal temperature (HOMEOSTASIS!)  Hydrogen bonds also decrease water’s tendency to evaporate, or vaporize.  Another way temperature is moderated by water is via evaporative cooling.  When a substance evaporates, the surface of the remaining behind cools down as the molecules with greatest energy leave.  Helps prevent overheating

Properties of Water Solvent  Water is known as the universal solvent, or dissolving agent.  When it is the solvent, the result is an aqueous solution.  Water’s versatility as a solvent results from the polarity of its molecules:  For example, Na+ attract the electronegative O of water molecules, and Cl- attract the positively charged H regions. As a result, H 2 O molecules surround and separate NaCl, dissolving the crystal in this process.  Blood and most other biological fluids are classified as aqueous solutions.

Properties of Water Other things about water…  Water exists in nature as a gas (water vapor, liquid, and solid)  Water is less dense as a solid than as a liquid.  Ice crystals have more spaciously arranged molecules, and water is more tightly packed. Therefore, there are fewer molecules in an ice cube than an equal volume of water. IceLiquid water

Acids Acids are compounds that contain hydrogen and can dissolve in water to release hydrogen ions into solution.  Increase the concentration of hydrogen ions  For example, hydrochloric acid (HCl) dissolves in water as follows:  HCl  H + (aq ) + Cl - (aq)

Bases Bases as substances that dissolve in water to release hydroxide ions (OH-) into solution.  decrease the concentration of hydrogen ions (by accepting them).  For example, a typical base according to the Arrhenius definition is sodium hydroxide (NaOH):  NaOH  Na + (aq) + OH - (aq)

pH Scale The acidity or basicity of something, therefore, can be measured by its hydrogen ion concentration. pH is a measure of the balance between hydrogen ions (H + ) and hydroxide ions (OH - ) in an aqueous solution.  Solutions with pH = 7 are neutral (for example, pure water)  Solutions with pH < 7 are acidic  Solutions with pH > 7 are basic (or “alkaline”)

Indicators Indicators:  used to determine pH.  change color, depending on the pH of the surrounding solution.  Is either a chemical or papers that is saturated with indicators, such as litmus paper and alkacid test paper

Buffers Buffers:  A buffer solution is one which resists changes in pH when small quantities of an acid or a base are added to it.  For example, your blood has buffers that help to ensure an optimal pH is maintained in your body.