ACADEMIC BIOLOGY BASIC CHEMISTRY

NOTES

ATOMS

A. An atom is the smallest particle of an element.

B. Arrangement1. Nucleus – The center of an

atom.

2. Proton – (+) charged particle found inside the nucleus.

3. Electron – (-)charged particle found outside the nucleus.

4. Neutron – Particle found in the nucleus with no charge.

C. Energy Levels

1. Regions where electrons travel around the nucleus.

2. Each energy level can only hold a certain number of electrons.

a. The first energy level can hold 2 electrons.

b. The second energy level can hold 8 electrons.

c. The third energy level can hold 18 electrons.

3. All energy levels being used must be full for an element to be stable.

Example:

If an element has 8 total electrons, 2 will be in the first energy level and the remaining 6 will be in the second. Is it stable?

Electron Configuration Examples:

1. Draw the electron configuration for an atom with 10 electrons. Is it stable?

2. Draw the electron configuration of an atom with 16 electrons. Is it stable?

ELEMENTS

A. A substance which cannot be broken down into simpler substances.

1. There are 90 naturally occurring ones in nature.

B. All elements are listed on the Periodic Table.

Elements

• Only 25 elements are needed for living things.

• 96% of the mass of a human being is composed of C,H,N and O.

D. Atomic Number

1. The number found above an element on the periodic table.a. Is equal to the total protons in a nucleus.b. Also indicates the

number of electrons since protons and electrons always equal one another.

E. Atomic Mass

1. The number found below an element on the periodic table.

a. Is equal to the total protons and neutrons in a nucleus.

Determining p+,n0,e-

• Protons are always = to atomic number

– Carbon’s atomic number is 6= 6 protons

• Electrons are also = to atomic number

– Unless an ion (+ or – charge)

• Neutrons= atomic mass – atomic number

– Carbon= 12 (at. Mass) – 6 (at.#) = 6 neutrons

IONS

• Ions are charged particles- caused by having more or less electrons.

• # of protons can never change

• + ions more protons than electrons

• - ions more electrons than protons

• Example- Na+2, how many protons and electrons?

Isotopes

• Different forms of an element due to varying numbers of neutrons. – Ex.- Carbon-12, Carbon-13 and Carbon-14

6p/6n 6p/7n 6p/8n

How Elements Combine

A. Compound1. A substance that is made of two or

more different elements bond together.

Example: Salt (NaCl) or Water (H2O)

B. Molecule

1. A group of atoms held together by covalent bonds.

Example: Oxygen (O2)

C. Covalent Bond

1. When two atoms share electrons.

Example: Water (H2O) 2. Strong bond

3. Found in organic compounds

4. Similar electronegativities

a. Polar Bond

- Occurs when the electrons of a bond are not shared equally.

- As a result, certain atoms will become slightly negative while others will become

slightly positive.

Example: Water (H2O)

b. Nonpolar Bond

- Occurs when the electrons of a bond are shared equally.

Example: Hydrogen Gas (H2)

D. Ionic Bond

1. When two elements of opposite charge combine.

2. An ion is an atom that has acquired a positive or negative charge.

Example: Na+ + Cl- = NaCl

E. Hydrogen Bonds

• Bonds that form between a hydrogen atom and another atom due to their high polarity.

• Holds water molecules together.• weak bond

WATER

A. Importance

1. Provides a place for chemical reactions to occur.2. Is a means of transport for organisms. (Blood)3. Makes up a large portion of living organisms. (75-90 %)

B. Hydrogen Bonds

1. Water molecules attract each other.2. The positively charged H atoms of one water molecule attract the negatively charged oxygen atoms of another water molecule.3. This bond is weak!4. Hydrogen bonds are important since they help hold many large molecules, such as proteins, together!

Polarity of H2O

• Water is polar due to the uneven distribution of charge. – Oxygen has a stronger pull on e- than

hydrogen so the oxygen side of the molecule has a slight negative charge.

Properties of Water

• Cohesion- attraction between molecules of the same substance.– Due to high polarity of water, can form up to 4

hydrogen bonds. – Causes water beading and

surface tension.

• Adhesion- attraction between molecules of different substances.– Causes meniscus in a graduated cylinder

and capillary action.

Properties of water

• High Specific Heat Capacity- due to the large number of hydrogen bonds water can absorb large amounts of heat.

• Evaporative cooling- as water evaporates it pulls heat from the environment.– Ex- sweating

• Versatile Solvent- Due to high polarity water is an excellent solvent.

Solutions

• Solutions are made up of a solute and a solvent.

• Solute- the substance that is being dissolved into the solution.– Ex- iced tea mix

• Solvent- the substance that is dissolving the solute.– Ex- Water.

• Water is always the solvent!

VI. pH (Acids & Bases)A. pH - Refers to the hydrogen ion (H+) versus hydroxide ion

(OH-) concentration in a solution.

* The pH scale ranges from 0-14.

B. Acid – A substance that has more H+ ions and has a pH below 7.

*HCl added to water will form H+ and Cl- ions.

C. Base – A substance that has more OH- ions and has a pH above 7.

*NaOH in water forms Na+ and OH- ions.

pH EXAMPLES:

– Pure water has a pH of 7.0. (Equal amounts of H+ and OH- ions.)

– Hair remover (Nair) has a pH of 13.0.

– Soda has a pH of 3.0.

Chemical Equations• C6H12O6 + 6O2 6CO2 + 6H2O + energy

Reactants Products

• Reactants are combining to form the products.

• Coefficients- the number that comes before the element or compound, affects all elements following.– Ex- 6CO2 , 6 x C= 6C and 6 x O2= 12 O

Chemical Equations Cont.

• C6H12O6 + 6O2 6CO2 + 6H2O + energy

Reactants Products

• Subscripts- the number attached to an individual element, shows the number of that element.– Ex O2 , O x 2= 2 oxygen