1. The Chemical Context of Life
Campbell Biology ninth ediction Chapter 2 pg 30-45

2. Chemical connection to Biology
Chemistry helps make Biology “work”.
Chemicals help with insect communication, attraction of mates, and defense against predators.
Some ants use formic acid as a disinfectant that protects against microbial parasites. The devil’s garden ant can use it as a herbicide.
Photosynthesis and other cellular processes
Digestive system runs on chemical reactions
And many more!

3. Matter consists of chemical elements in pure form and in combinations called compounds
Organisms are composed of matter
Matter is anything that takes up space and has mass
Matter has many forms such as rocks, metals, gases and humans.

4. Elements and Compounds
Matter is made up of elements.
An element is a substance that cannot be broken down to other substances by chemical reactions.
There are 92 elements occurring in nature.
A compound is a substance consisting of two or more different elements combined in a fixed ration. (Ex: NaCl sodium+ chlorine)
A compound has characteristics different from those of its elements.

5. The Elements of Life
Essential elements are those that an organism needs to live a healthy life and to reproduce.
Only 20-25% of the natural elements are essential.
Trace elements are required by an organism in small quantities.
Ex: Iodine (I) is an essential ingredient of a hormone produced by the thyroid gland. Humans only need 0.15 mg daily.
Some naturally occurring elements can be toxic such as arsenic.

6. An Element’s Properties depends on the Structure of its Atoms
An atom is the smallest unit of matter that still retains the properties of an element.
Each element consists of a certain type of atom that is different from the atoms of any other element.

7. Subatomic Particles
Atoms are composed of even smaller parts, called subatomic particles.
Neutrons: no charge
Protons: positive charge
Electrons: negative charge
Protons and neutrons are packed together in a dense core at the center of the atom called the atomic nucleus.
Electrons are located around the nucleus.

8. Atomic Number and Atomic Mass
All atoms of a particular element have the same number of protons in their nuclei. The number of protons is called the atomic number.
In a neutral atom, the atomic number will also tell the number of electrons.
The mass number is the sum of protons plus neutrons. The number of neutrons is determined by subtracting the protons from the mass number.
The mass number is an approximation of the total mass of an atom, called the atomic mass.

9. Isotopes
All atoms of an element have the same number of protons, but may have a greater number of neutrons and therefore a greater mass. These different atomic forms of the same element are called isotopes.
Even though isotopes may have a slightly different mass, they behave the same in chemical reactions.
A stable isotope means the nucleus does not tend to lose particles.
An unstable or radioactive isotope is one in which the nucleus decays, giving off particles of energy.
When a decay leads to a change in the number of protons, the atom transforms to a different element. (radioactive carbon to nitrogen)
Radioactive isotopes are useful in biology. ( fossil dating, tracers, diagnostic tools)

10. The Energy Levels of Electrons
Electrons vary in the amount of energy they possess. Energy is defined as the capacity to cause change.
Potential energy is the energy that matter possesses because of its location or structure.
The electrons of an atom have potential energy due to their arrangement in relation to the nucleus.
The greater the distance an electron is from the nucleus, the greater its potential energy which is determined by energy levels.
Electrons are found in different electron shells, each with a characteristic average distance and energy level.
When an electron loses energy, it “falls back” to a shell closer to the nucleus, and the energy is usually released as heat into the environment.

11. Electron Distribution and Chemical Properties
The distribution of electrons in the electron shell determines the chemical behavior of an atom.

12. Electron Distribution and Chemical Properties
The chemical behavior of an atom depends mostly on the number of electrons in its outermost shell.
The outermost electrons are called valence electrons and the outermost shell is called the valence shell.
At atom with a completed valence shell is unreactive, meaning it will not react readily with other atoms. (Ex: Helium (He), Neon (Ne) and Argon (Ar)

13. Electron Orbitals
The exact location of an electron will never be known, but we can describe the space in which it spends most of its time.
The three dimensional space where an electron is found 90% of the time is called an orbital.
The reactivity of atoms arises from the presence of unpaired electrons in one or more orbitals of their valence shells.
Atoms interact to complete their valence shells.

14. The Formation and Function of molecules depend on chemical bonding between atoms
Atoms either share or transfer valence electrons.
These types of interactions result in atoms staying close together, held by attractions called chemical bonds.
The strongest chemical bonds are covalent bonds and ionic bonds.

15. Covalent Bonds
A covalent bond is the sharing of a pair of valence electrons by two atoms.
Two hydrogen atoms will share their valence electrons so that they will each have a complete valence shell.
Two or more atoms held together by covalent bonds constitute a molecule. (Ex: Molecular formula H2 ; Lewis dot structure H:H; structural formula H-H)
In a structural formula a single line represents a single bond, a pair of shared electrons. When atoms form a molecule by sharing two pairs of valence electrons they are joined by a double bond. (O=O)

16. Covalent Bonds cont.
Each atom that can share valence electrons has a bonding capacity corresponding to the number of covalent bonds the atom can form. This bonding capacity is called the atom’s valence and usually equals the number of unpaired electrons required to complete the atom’s outermost shell.
The attraction of a particular atom for the electrons of a covalent bond is called it electronegativity. The more electronegative an atom is, the stronger it pulls shared electrons toward itself.
A nonpolar covalent bond is a type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.
When one atom is bonded to a more electronegative atom, the electrons of the bond are not shared equally. This is a polar covalent bond.

17. Ionic Bonds
Sometimes two atoms are unequal in their attraction for valence electrons that the more electronegative atoms will strip an electron completely away from its partner. (Ex: Sodium has a single valence electron and chlorine as 7 valence electrons. Chlorine will take the single electron from sodium, and therefore they both will have complete valence shells)
A charged atom or molecule is called an ion. (Ex: Sodium now has 11 protons and only 10 electrons so it has a 1+ charge)
When the charge is positive it is called a cation.
When the charge is negative it is called an anion.
Because of their opposite charges, cations and anions attract each other. This is called an ionic bond.

18. Ionic Bonds Cont.
Compounds formed by ionic bonds are called ionic compounds, or salts.
Salts are often found in nature as crystals.
Environment affects the strength of ionic bonds. (ex: hard when dry but can dissolve in water)

19. Weak Chemical Bonds
Many large biological molecules are held in their functional form by weak bonds.
Weak bonds allow two molecules to come together and then separate.
Hydrogen bonds and van der Waals interactions are crucial to life.

20. Hydrogen Bonds
The noncovalent attraction between a hydrogen and an electronegative atom is called a hydrogen bond.
In living cells, the electronegative partners are usually oxygen or nitrogen atoms.

21. Van der Waals Interactions
Van der Waals interactions are weak attractions between molecules or parts of molecules that result from transient local partial charges.
Only occur when particles are very close together.
These reactions are why a gecko lizard can walk up a wall.

22. Molecular Shape and Function
A molecule has a characteristic size and shape. The shape is important to its function in the living cell.
Shapes are determined by the positions of the atoms’ orbitals.
Molecular shape is important in biology because it determines how biological molecules recognize and respond to one another.
Biological molecules can only form weak bonds if their shapes are complementary.
Opiates, such as morphine, relieve pain and alter mood by weakly binding to specific receptor molecules on the surfaces of brain cells.

23. Chemical reactions make and break chemical bonds
The making and breaking of chemical bonds, which leads to changes in the composition of matter, are called chemical reactions.
The covalent bonds of hydrogen and oxygen and broken to form the new bond of water.
An arrow indicates the conversion of the starting materials, called the reactants, to the products. Coefficients indicate the number of molecules involved.

24. Chemical reactions make and break chemical bonds cont.
A factor affecting the rate of a reaction is the concentration of reactants.
The greater the concentration of reactant molecules, the more frequently they collide with one another and have the opportunity to react.
Eventually the forward and reverse reactions occur at the same rate, and the relative concentrations of products and reactants stop changing.
The point at which reactions offset each other exactly is called chemical equilibrium.
Equilibrium does not mean that the reactants and products are equal in concentration, but only that their concentrations have stabilized at a particular ratio.

25. Question 1 In the term trace element, the adjective trace means that
A. the element is required in very small amounts
B. the element can be used as a label to trace atoms through an organism’s
metabolism.
C. the element is very rare on Earth.
D. the element enhances health but is not essential for the organism’s
long-term survival

26. Question 2 Which of the following are examples of weak bonds
A. covalent and ionic bonds
B. covalent and hydrogen bonds
C. hydrogen bonds and Van der Waals interactions
D. only hydrogen bonds

27. Question 3 When do chemical bonds form?
A. when pairs of electrons are shared
B. when electrons become charged
C. when atoms have complete valence shells
D. when atoms interact to complete their valence shells

28. Cheeseburger in Hydrochloric Acid