Unit 1 Biology Notes

Study these items as an overview for textbook chapters 2.1 - 2.5. Use this to prepare for the quiz and possibly for the exam. Read slowly and carefully as definitions will overlap.

What physically distinguishes one element from another?

The number of protons in the nucleus, known as the atomic number, which defines each element and determines its chemical properties.

Explain the concept of an emergent property.

A characteristic that a complex system has, but the individual parts do not have on their own.

Protons

Positively charged particles in the nucleus, define the atom's identity/atomic number, and have a mass of roughly 1 Dalton.

Electron

Negatively charged, virtually massless particles that move rapidly outside the nucleus.

Neutrons

Electrically neutral particles in the nucleus, contribute to stability and mass. (Also 1 Dalton)

Describe the arrangement of the protons, neutrons and electrons in the nucleus of an atom.

Protons and Neutrons are tightly packed at the center of the atom to form the "core” Called the Atomic nucleus. Electrons are not located in the nucleus; instead, they form a cloud around it.

Mass number

An exact whole number representing the total count of protons plus neutrons in the atom.

Atomic mass

 The actual total mass of an atom, measured in daltons.

Correlate the energy of an electron with its position around the atom.
Lower.

Closer to the nucleus, lower potential energy.

Correlate the energy of an electron with its position around the atom.
Higher.

Farther from the nucleus, greater potential energy.

Explain what a covalent bond is.

The sharing of a pair of valence electrons by two atoms to complete their outer shells.

Electronegativity

The measure of an atom's attraction for the shared electrons of a covalent bond.

Polar covalent bond

Happens when one atom is significantly more electronegative than the other, causing unequal sharing of electrons.

Nonpolar covalent bond

Occurs between atoms with simılar electronegativities, resulting in sharing equal electrons.  

Electronegativity patterns

Oxygen pulls electrons strongly, forming polar bonds with carbon (nonpolar), hydrogen (nonpolar), and nitrogen.

Describe an ionic bond.

When two atoms differ strongly in electronegativity, so one atom completely strips an electron away from the other to create two oppositely charged ions.

Describe a hydrogen bond.

A weak noncovalent attraction between a hydrogen atom that is already covalently bound to an electronegative atom.

Valence shell

Outermost layer of an electron shell.

Describe what a chemical reaction is.

 The transformation of one chemical to another by making and breaking chemical bonds.

Reactants

The starting materials in a reaction, usually before the tall of the arrow, to the left.

Products

The result of the reaction, usually at the point of the arrow.

Give an example of products and reactants.

2H2 and 02 are reactants, 2H20 is the product.

Chemical equilibrium

A reversible reaction where the forward reaction and the reverse reaction occur at the same rate.

Identify the four positions of hydrogen bonds between 5 water molecules.

Two hydrogen bonds via the 2 partial posıtive hydrogen atoms, bonding to neighboring oxygen atoms.

Two hydrogen bonds via the 2 partial negative regions on the oxygen atom bonding to hydrogen atoms or neighboring molecules.

Cohesion

Attraction between like (similar) molecules.

Adhesion

Attraction between different substances.

Distinguish between the type of bond that holds a water molecule together and the type of bond that holds two water molecules to each other.

Intramolecular - In a single water molecule, polar covalent bonds hold the hydrogen and oxygen atoms through unequal sharing of electrons.

Intermolecular- Between two water molecules, hydrogen bonds hold separate water molecules together through the attraction between opposite partial charges.

Heat

Reflects the total Kinetic energy moved between objects, which depends on volume

Temperature

Measures the average kinetic energy of molecules in a body of matter, regardless of mass.

Why does ice float in water?

As water cools to 0°C, hydrogen bonds stabilize and lock water molecules into a crystalline lattice. This keeps molecules further apart, making ice 10% less dense than water at 4°C, if water did not form hydrogen bonds, it would sink; bodies of water would freeze solid from the bottom up, eliminating the insulating layer above and destroying aquatic habitats.

Describe why water is a good solvent.

Because of polarity. Its partıal positive and negative charges surround charged or polar solute particles, making hydration shells that separate and dissolve ions polar molecules.

Acid

A substance that increases the concentration of hydrogen ions in a solution.

Base

 A substance that reduces the concentration of hydrogen ions.

Explain where an acid and base falls on the pH scale.

Acid - Falls below 7

Bases- Fall above 7

Neutral - things like water, sits exactly at 7