Biology Ch2 Basic Chem

Matter

Anything that has mass and occupies space.

Element

A substance that cannot be broken down into substances with different properties; it is composed of one type of atom.

CHNOPS

The six elements that make up about 95% of the body weight of organisms: Carbon

Atom

The smallest part of an element that displays the properties of that element.

Subatomic particles

The particles that make up atoms: protons

Proton

A positively charged subatomic particle located in the nucleus of an atom; it has a mass of about 1 atomic mass unit (AMU).

Neutron

A subatomic particle with no charge located in the nucleus of an atom; it has a mass of about 1 AMU.

Electron

A negatively charged subatomic particle found in electron shells around the nucleus; it has very little mass compared with protons and neutrons.

Nucleus

The central part of an atom that contains protons and neutrons.

Electron shell

An energy level around the nucleus where electrons are found.

Potential energy

Energy an electron has because of its relative position.

Bohr model

A model used to visualize the location of electrons in energy shells around an atom's nucleus.

Energy shell

A region around the nucleus where electrons with similar energy levels are found.

Valence shell

The outermost energy shell of an atom; it determines many of the atom's chemical properties.

Valence electrons

The electrons located in an atom's outermost energy shell.

First energy shell

The first electron shell

Additional energy shells

For atoms with atomic numbers of 20 or less each additional energy shell can hold up to 8 electrons.

Octet rule

The principle that an atom's outermost shell is most stable when it contains 8 electrons.

Exception to the octet rule

An atom with only one electron shell has a complete outer shell when it contains 2 electrons.

Chemically stable atom

An atom whose valence shell is filled with electrons.

Chemically reactive atom

An atom whose valence shell is not filled with electrons.

Atomic symbol

A one- or two-letter abbreviation used to represent an element.

Atomic number

The number of protons in the nucleus of an atom. In a neutral atom it also equals the number of electrons.

Mass number

The total number of protons plus neutrons in an atom's nucleus.

Atomic mass

The mass of an atom which is approximately equal to its mass number.

Isotope

Atoms of the same element that have different numbers of neutrons and therefore different atomic masses.

Radioactive isotope

An isotope that spontaneously decays and gives off energy in the form of rays and subatomic particles.

Carbon-14

A radioactive isotope of carbon that has been used to examine reactions in photosynthesis.

Periodic table

A chart that organizes elements according to their atomic numbers and chemical properties.

Group

A vertical column on the periodic table. Elements within the same group have similar chemical binding characteristics.

Period

A horizontal row on the periodic table.

Noble gases

Elements in Group VIII that are generally inert because their valence shells are filled.

Neutral atom

An atom with equal numbers of protons and electrons giving it no overall electrical charge.

Chemical reactivity

The tendency of an atom to participate in chemical reactions based largely on the state of its valence shell.

Molecule

Two or more atoms of the same type bonded together; it is the smallest part of a substance that retains its chemical properties.

Compound

A molecule containing at least two different elements bonded together.

Chemical formula

A notation that tells the number of each type of atom in a molecule.

Chemical bond

An attraction that holds atoms together; bonds contain energy and result from interactions between electrons in the outermost energy shells.

Chemical reaction

The process involved in the formation or breaking of chemical bonds.

Ion

An atom that has gained or lost one or more electrons and therefore has an electrical charge.

Cation

A positively charged ion formed when an atom loses one or more electrons.

Anion

A negatively charged ion formed when an atom gains one or more electrons.

Ionic bond

A bond formed when electrons are transferred from one atom to another causing oppositely charged ions to attract each other.

Sodium chloride (NaCl)

A salt formed when sodium transfers an electron to chlorine producing Na⁺ and Cl⁻ ions that attract each other.

Salt

A solid substance that usually separates and exists as individual ions when dissolved in water.

Covalent bond

A bond in which two atoms share electrons so that each atom can have a complete outer shell.

Nonpolar covalent bond

A covalent bond in which electrons are shared equally between atoms.

Polar covalent bond

A covalent bond in which electrons are shared unequally between atoms.

Electronegativity

The ability of an atom to attract electrons toward itself in a chemical bond.

Hydrogen gas (H₂)

An example of a molecule containing a nonpolar covalent bond because the two hydrogen atoms share electrons equally.

Oxygen gas (O₂)

An example of a molecule with a nonpolar covalent bond between two oxygen atoms.

Methane (CH₄)

A molecule in which carbon forms covalent bonds with four hydrogen atoms.

Water (H₂O)

A polar molecule in which oxygen attracts the shared electrons more strongly than hydrogen.

Polarity

The uneven distribution of electrical charge within a molecule.

Partial positive charge (δ⁺)

The slight positive charge that occurs in part of a polar molecule such as the hydrogen atoms in water.

Partial negative charge (δ⁻)

The slight negative charge that occurs in part of a polar molecule such as the oxygen atom in water.

Hydrogen bond

A weak attraction between a slightly positive hydrogen atom and a slightly negative atom; it can occur between different molecules or within the same molecule.

Importance of hydrogen bonds

Hydrogen bonds help maintain the proper structure and function of complex molecules such as proteins and DNA.

Water's high heat capacity

The ability of water to absorb a large amount of thermal energy without a large change in temperature because many hydrogen bonds must be broken.

Evaporation

The process in which water molecules escape as a gas; it requires energy to break hydrogen bonds.

Evaporative cooling

The cooling of an organism when heat energy is used to evaporate water such as during sweating.

Ice

Water in its solid form; its hydrogen bonds form a more open structure making ice less dense than liquid water.

Why ice floats

Ice is less dense than liquid water because hydrogen bonds hold water molecules in an open structure when water freezes.

Water as a solvent

Water is a good solvent because its polarity allows it to dissolve many polar and ionic substances.

Solvent

The substance that does the dissolving in a solution.

Solute

The substance that is dissolved in a solution.

Solution

A mixture containing dissolved substances or solutes.

Cohesion

The ability of water molecules to cling to each other because of hydrogen bonding.

Surface tension

The resistance of a water surface to being broken or stretched caused by cohesion between water molecules.

Adhesion

The ability of water molecules to cling to other polar surfaces.

Capillary action

The movement of water through narrow spaces caused by the combined effects of adhesion and cohesion.

Water transport in plants

The movement of water through plants helped by cohesion between water molecules and adhesion between water and the sides of vessels.

High heat capacity

Water's ability to absorb substantial amounts of heat without a major increase in temperature.

Water's unusual freezing behavior

Below 4°C hydrogen bonds become more rigid and open causing water to expand as it approaches 0°C and freezes.

Insulating property of ice

Because ice is less dense and floats it can form an insulating layer on top of liquid water.

pH

A measure of hydrogen ion (H⁺) concentration in a solution.

Ionization of water

The process in which water dissociates into equal numbers of hydrogen ions (H⁺) and hydroxide ions (OH⁻).

Hydrogen ion (H⁺)

A positively charged ion involved in determining the acidity of a solution.

Hydroxide ion (OH⁻)

A negatively charged ion involved in determining the basicity of a solution.

pH scale

A scale from 0 to 14 used to indicate how acidic or basic a solution is.

Neutral pH

A pH of 7 where the concentration of H⁺ equals the concentration of OH⁻.

Acid

A substance that dissociates in water and releases hydrogen ions (H⁺).

Basic/alkaline

A substance that either takes up hydrogen ions or releases hydroxide ions (OH⁻).

Acidic pH

A pH below 7.

Basic pH

A pH above 7.

Logarithmic pH scale

A scale in which each one-unit change in pH represents a 10-fold change in hydrogen ion concentration.

pH 5 vs. pH 7

A solution with pH 5 is 100 times more acidic than a solution with pH 7.

pH 4 vs. pH 5

A solution with pH 4 is 10 times more acidic than a solution with pH 5.

Buffer

A chemical or combination of chemicals that helps keep pH within normal limits.

Importance of buffers

Buffers help organisms maintain the pH of body fluids within narrow limits.

Normal human blood pH

About 7.4 which is slightly basic.

Acidosis

A potentially life-threatening condition that occurs when blood pH drops below 7.0.

Alkalosis

A potentially life-threatening condition that occurs when blood pH rises above 7.8.

Carbonic acid buffer

A body buffer system that can dissociate and reform to help reduce changes in pH.

Atomic number vs. mass number

Atomic number equals the number of protons; mass number equals protons plus neutrons.

Protons and electrons in a neutral atom

A neutral atom has equal numbers of protons and electrons.

How to calculate neutrons

Number of neutrons = mass number − atomic number.

How atoms become ions

Atoms become ions by gaining or losing electrons; the number of protons does not change.

What determines chemical behavior

The electrons in an atom's outermost energy shell especially the valence electrons.

What happens when an atom loses electrons

It becomes a positively charged ion or cation.