Chemistry for Biology Chapter 2

KEY CONCEPT All living things are based on atoms and their interactions.

Living things consist of atoms of different elements. An atom is the smallest basic unit of matter. An element is one type of atom. Hydrogen atom (H) H O Oxygen atom (O)

An atom has a nucleus and electrons. The nucleus contains the protons and neutrons. Electrons are in energy levels outside nucleus. Oxygen atom (O) Nucleus: 8 protons (+) 8 neutrons outermost energy level: 6 electrons (-) inner energy level: 2 electrons (-)

What is the mass of the atomic particles? Protons and neutrons each weigh 1 amu (atomic mass unit or Dalton). Electrons are basically mass-less and exist as clouds circulating around the nucleus.

What about elements? Elements cannot be broken down into any other substances. There are 92 naturally occurring elements on our earth. Some of the most important to the living world are hydrogen (H), carbon (C), oxygen (O), nitrogen (N), and phosphorus (P).

An element is identified by its number of PROTONS which is its atomic number on the Periodic Table of the Elements.

The atomic mass is indicated below the symbol. It is equal to the number of protons and neutrons (since the electrons are essentially mass-less).

What is the number of? Protons Electrons Neutrons

What is an isotope? Isotopes are different forms of an element that differ by their ATOMIC MASS and their number of NEUTRONS.

Isotopes of Carbon

What are isotopes used for in biology? Dating or aging rocks and fossils Tracing the paths of atoms and molecules in living things Killing cancer cells Some isotopes are radioactive!

Using radioactive iodine to trace function of the thyroid gland.

Do atoms have charges? Atoms are usually electrically neutral since the number of their protons (+) is equal to their number of electrons (-).

How are the electrons arranged around the nucleus of the atom? Electrons are located on levels or shells around the nucleus of the atom. The electrons located on the closest level have less energy than those on the farthest levels.

How many electrons can each level hold? TWO on the first EIGHT on the second And in the elements we study in biology, EIGHT on the third level.

The arrangement of electrons in oxygen and hydrogen. Oxygen atom Hydrogen atom

Magnesium 12 electrons – 2,8,2

Elements with their outer electron levels full are said to be INERT and do not react. For example Neon has 10 electrons: 2 on the first level and 8 on the second level. It does not react with other elements.

Atoms will bond with other atoms to fill their outer electron levels.

Types of bonds: Sometimes atoms will transfer electrons to fill their outer levels. This is called an IONIC BOND Charged atoms are called ions.

An ionic bond

Ions form when atoms gain or lose electrons. An ion is an atom that has gained or lost one or more electrons. positive ions (cations) negative ions (anions) Ionic bonds form between oppositely charged ions. Sodium atom (Na) Chlorine atom (CI) Sodium ion (Na+) Chloride ion (CI-) Na loses an electron to CI ionic bond gained electron

Atoms share pairs of electrons in covalent bonds. A covalent bond forms when atoms share a pair of electrons. Covalent bonds are stronger than ionic bonds.

Covalent Bond in Hydrogen gas H2

Covalent Bonds Each covalent bonds represents TWO shared electrons. Atoms can share two pairs of electrons and form a DOUBLE bond. Atoms can share three pairs of electrons and form a TRIPLE bond. Six shared electrons

Covalent bonds

A molecule of CO2 with a double bond between the carbon and oxygen atoms.

Most molecules in living things are covalently bonded.

Each Carbon makes ____ bonds, oxygen ___________ bonds, hydrogen ___________ bonds, and nitrogen ________ bonds. 4 2 1 3

Van der Waal forces are attractions between molecules due to unbalanced charges in the molecules.

Who uses Van der Waal forces?

A compound is made of atoms of different elements bonded (chemically combined) together. water (H2O) O H _ +

carbon dioxide (CO2)

A MOLECULE is the smallest unit of a compound A MOLECULE is the smallest unit of a compound. It usually is used to indicate a covalently bonded molecule. When two or more elements are physically combined, a MIXTURE results.

Compounds and Mixtures Water molecule – a compound H2O A mixture of water and salt.

Chemical bonds form in chemical reactions. Chemical reactions are represented by EQUATIONS. Chemical equations have to be balanced because matter is neither created or destroyed in chemical reactions.

Balance these equations: Na + Cl2 NaCl (sodium chloride)   H2 + O2 H2O

Balance these equations: Na + I2 NaI N2 + O2 N2O N2 + H2 NH3 CH4 + O2 CO2 + H2 O KI + Cl2 KCl + I2

S + O2 SO3 H2O2 H2O + O2 Na + H2 O NaOH + H2

Balance these equations: 2Na + I2 2NaI 2N2 + O2 2N2O N2 + 3H2 2NH3 CH4 + 2O2 CO2 + 2H2 O 2KI + Cl2 2KCl + I2

2S + 3O2 2SO3 2H2O2 2H2O + O2 2Na + 2H2 O 2NaOH + H2

An example of a chemical reaction:

Water The most abundant compound in living things and covers ¾ of the earth’s surface. Is made of 2 hydrogen atoms covalently bonded to one oxygen atom.

Water is a POLAR molecule. Why? Most of the electrons tend to stay near the oxygen and therefore the oxygen part of the molecule has a NEGATIVE charge with the hydrogen atoms having a POSITIVE charge. H H Oxygen

What are hydrogen bonds? Hydrogen bonds form between a hydrogen atom in one molecule to an oxygen (or electron-grabby element) in another molecule. They form BETWEEN MOLECULES - not like covalent and ionic bonds. Water molecules attract each other through hydrogen bonding.

Water molecules stick to each other with HYDROGEN bonds Water molecules stick to each other with HYDROGEN bonds. This is called COHESION.

The cohesion property of water causes capillarity and surface tension.

Water can also stick to other substances. This is called adhesion.

Due to hydrogen bonds, it takes a lot of heat to break the hydrogen bonds so water has a high SPECIFIC HEAT which is the amount of calories needed to raise one gram of water one degree Celsius. This keeps water a moderate temperature for living organisms that live in water.

Water is a good solvent. The solute is what is being dissolved. Solutions – the substance is dissolved in water Suspension – particles are not dissolved but “suspended” in solution (ex, blood)

Solution – the solute is completely dissolved Suspension – particles not dissolved

Water will mix with other polar molecules but not with nonpolar molecules such as fats and oils.

What will water dissolve? Other polar molecules Ionic compounds WHY? Because these have charges in their molecules and attract the polar water. http://programs.northlandcollege.edu/biology/Biology1111/animations/dissolve.swf

The ionization of water Water can ionize (change into ions) into hydrogen ions and hydroxide ions. H2O H+ + OH- hydrogen ions hydroxide ions The amount of these ions determine if a solution is acidic or basic which is detected by a measure of pH (pH meter, pH paper).

pH meter and paper

pH scale – measures amount of H+ ions in a solution. 1 7 14 MORE H+ ions LESS H+ ions ACID BASE Each unit represents a 10 times difference since the pH scale is based on a logarithm scale (10 based)!

pH scale Vinegar is 10 times more acidic than tomato juice. How much more basic is oven cleaner (14) than Milk of Magnesia (10)?

Solution Amount of H+ ions and OH- ions pH Acidic More H+ ions Below 7 Basic Less H+ ions Above 7 Neutral Equal number of H+ and OH- ions. 7

pH of some common items

What is the pH of the interior of cells? Around 6 - 8

What is the pH of blood? Between 7.35 and 7.45 So, what happens when you drink or eat acidic substances? Why doesn’t your blood pH drop? Because living things contain buffers!

What are buffers? Buffers are substances that keep the pH regulated by resisting changes in pH. If too acidic, they will pick up hydrogen ions. If too basic, they will put hydrogen ions back into solution. They maintain homeostasis in living things. They’re like little Chemists in your body keeping those H+ regulated!

What happens when acid is added to a solution with a buffer What happens when acid is added to a solution with a buffer? HCl is hydrochloric Acid. 1 2 3 4 5 6 Drops of acid