Bio chapter 2

Matter

The substance of which any physical object is composed; any material that has mass and takes up space.

Mass

The amount of matter in an object, often measured in grams or kilograms; different from weight because mass does not depend on gravity.

Atoms

The smallest units of matter that have the properties of a chemical element; all matter is composed of atoms.

Why atoms matter in biology

Understanding atomic structure is important because biological molecules are built from atoms and their chemical behavior depends on atomic structure.

Subatomic particles

The smaller particles that make up atoms: protons, neutrons, and electrons.

Protons

Positively charged subatomic particles located in the nucleus of an atom; the number of protons determines the element's atomic number.

Neutrons

Neutral subatomic particles located in the nucleus of an atom; they contribute to atomic mass and can vary among isotopes.

Electrons

Negatively charged subatomic particles found in orbitals surrounding the nucleus; they determine much of an atom's chemical behavior.

Nucleus

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

Orbitals

Regions of space around the nucleus where electrons are likely to be found; each orbital can hold a maximum of two electrons.

Element

A substance that cannot be broken down into any other substance by ordinary chemical means.

Atomic number

The number of protons in an atom; every atom of a particular element has the same atomic number.

Electrically neutral atom

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

Mass vs. weight

Mass is the amount of substance in an object, while weight is the force gravity exerts on that substance.

Atomic mass

The sum of protons and neutrons in an atom; electrons contribute very little mass.

Dalton (Da)

A unit used to measure atomic mass; each proton or neutron has a mass of about 1 Dalton.

Electron mass

Electrons have very little mass compared with protons and neutrons, about 1/1840 of a Dalton.

Ion

An atom or group of atoms that carries an electric charge because it has gained or lost electrons.

Cation

A positively charged ion with more protons than electrons; forms when an atom loses electrons.

Anion

A negatively charged ion with fewer protons than electrons; forms when an atom gains electrons.

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Radioactive isotopes

Unstable isotopes that emit radiation as their nuclei break apart.

Carbon-12

A stable carbon isotope that makes up about 99% of carbon found in nature.

Carbon-13

A stable carbon isotope that makes up most of the remaining naturally occurring carbon.

Carbon-14

A rare, unstable carbon isotope that breaks down into elements with lower atomic numbers.

Radioactive decay

The spontaneous breakdown of an atomic nucleus, releasing energy and matter from the nucleus.

Half-life

The time it takes for one-half of the atoms in a radioactive sample to decay.

Electrons and chemical reactions

The number and arrangement of electrons in orbitals determine the chemical behavior and reactions of atoms.

Atomic orbital

A region around the nucleus where an electron is likely to be found; orbitals come in different shapes such as s, p, d, and f.

Maximum electrons per orbital

Each atomic orbital can contain a maximum of two electrons.

Orbital shapes

Orbitals have different three-dimensional shapes and are labeled s, p, d, and f.

Electron energy level

The potential energy level of an electron based on its position relative to the nucleus.

Electron distance and energy

Electrons farther from the nucleus have more energy than electrons closer to the nucleus.

Energy levels vs. orbitals

Energy levels are often drawn as rings to show electron energy, while orbitals are three-dimensional regions showing where electrons are likely located.

Redox reaction

A chemical reaction in which electrons are transferred from one atom or molecule to another.

Oxidation

The loss of an electron; remembered by OIL in OIL RIG.

Reduction

The gain of an electron; remembered by RIG in OIL RIG.

OIL RIG

A memory device for redox reactions: Oxidation Is Loss, Reduction Is Gain of electrons.

Periodic table

A chart that organizes elements, partly according to their valence electrons and chemical properties.

Valence electrons

Electrons in the outermost energy level of an atom; they are most involved in chemical bonding and reactivity.

Octet rule

The tendency of atoms to establish completely full outer energy levels, usually with eight valence electrons.

Inert elements

Nonreactive elements that already have full outer energy levels, often eight valence electrons.

Highly reactive elements with 7 valence electrons

Elements with seven valence electrons tend to take one electron from another element to complete their outer energy level.

Highly reactive elements with 1 valence electron

Elements with one valence electron tend to give up that electron to another element.

Elements in living organisms

Although about 90 elements occur naturally, only 12 are found in living organisms in substantial amounts.

Four major elements in the human body

Carbon, hydrogen, oxygen, and nitrogen make up about 96.3% of human body weight.

Organic molecules

Biological molecules that contain primarily carbon, hydrogen, oxygen, and nitrogen.

Trace elements

Elements needed only in very small amounts but still very important for living organisms.

Chemical bonds

Attractive forces that hold atoms together in molecules or compounds.

Molecule

A group of atoms held together in a stable association.

Compound

A molecule containing more than one type of element.

Electron configuration

The arrangement of electrons in an atom's orbitals, which helps predict valence electrons and reactivity.

Ionic bond

A chemical bond formed by the attraction of oppositely charged ions after electrons are transferred.

Formation of ionic bonds

One atom loses electrons and becomes positive, while another gains electrons and becomes negative; the opposite charges attract.

Sodium chloride ionic bond

Sodium loses an electron to become Na+, chlorine gains an electron to become Cl−, and the opposite charges keep them associated as NaCl.

Water and ionic bonds

Water can easily disrupt ionic interactions because it interacts with charged ions.

Covalent bond

A chemical bond formed when atoms share two or more valence electrons.

Covalent bonds and net charge

Covalent bonds usually result in no net charge because electrons are shared rather than fully transferred.

Covalent bonds and the octet rule

Covalent bonding can satisfy the octet rule by allowing atoms to share electrons and fill outer energy levels.

Unpaired electrons in covalent bonds

Stable covalent bonding helps eliminate unpaired electrons by sharing electrons between atoms.

Single bond

A covalent bond in which one pair of electrons is shared between atoms.

Double bond

A covalent bond in which two pairs of electrons are shared between atoms.

Triple bond

A covalent bond in which three pairs of electrons are shared between atoms.

Bond strength in covalent bonds

The strength of a covalent bond depends partly on the number of shared electrons; more shared pairs generally means a stronger bond.

Biological compounds and covalent bonding

Many biological compounds contain more than two atoms and may share electrons with two or more atoms.

Electronegativity

An atom's affinity or attraction for electrons.

Electronegativity and covalent bonds

Differences in electronegativity determine whether electrons are shared equally or unequally in covalent bonds.

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 because one atom is more electronegative than the other.

Ionic bonds and electronegativity

Ionic bonds form when large electronegativity differences cause electrons to be transferred rather than shared.

Amine group bonds

An amine group has nitrogen bonded to hydrogens; these N-H bonds are polar covalent because nitrogen is more electronegative than hydrogen.

Chemical reaction

A process involving the formation or breaking of chemical bonds.

Atoms in chemical reactions

During chemical reactions, atoms shift from one molecule to another without changing the number or identity of atoms.

Reactants

The original molecules or substances that enter a chemical reaction.

Products

The molecules or substances that result from a chemical reaction.

Photosynthesis equation

6H2O + 6CO2 → C6H12O6 + 6O2; water and carbon dioxide are reactants, while glucose and oxygen are products.

Factors regulating chemical reactions

Temperature, concentrations of reactants and products, and catalysts influence the extent and speed of chemical reactions.

Reversible reactions

Many chemical reactions can proceed in both directions, from reactants to products and from products back to reactants.

Catalyst

A substance that affects the rate of a chemical reaction without being consumed in the reaction.

Water and life

Life is closely tied to water; about two-thirds of organisms' bodies are composed of water.

Most important chemical property of water

Water's ability to form hydrogen bonds is its most outstanding chemical property.

Hydrogen bond

A weak chemical association that forms between a partially negative atom, such as oxygen, and a partially positive hydrogen atom.

Hydrogen bonds between water molecules

Hydrogen bonds form between the partially negative oxygen of one water molecule and the partially positive hydrogen of another water molecule.

Polarity of water

Water is polar because oxygen is more electronegative than hydrogen, creating partial charges within the molecule.

Oxygen in water

The oxygen atom in water is partially negative because it attracts shared electrons more strongly than hydrogen.

Hydrogen in water

The hydrogen atoms in water are partially positive because oxygen pulls shared electrons away from them.

Weak but important water interactions

Individual hydrogen bonds are weak and temporary, but their cumulative effects give water many important properties.

Cohesion

The attraction of water molecules to each other due to hydrogen bonding.

Water as liquid at moderate temperatures

Cohesion between water molecules helps water remain liquid at moderate temperatures.

Surface tension

The property of a liquid surface that allows it to resist an external force because of cohesion among its molecules.

Adhesion

The attraction of water molecules to other polar molecules.

High specific heat of water

Water must absorb or lose a large amount of energy to change temperature, helping organisms maintain stable internal temperatures.

Specific heat

The amount of energy a substance must absorb or lose to change its temperature.

High heat of vaporization

Water requires a large amount of energy to change from liquid to gas.

Heat of vaporization

The amount of energy required to change 1 gram of a substance from liquid to gas.

Evaporative cooling

The evaporation of water from a surface removes heat and cools that surface.

Solid water density

Solid water is less dense than liquid water, which is why ice floats.

Freezing of bodies of water

Because ice is less dense than liquid water, bodies of water freeze from the top down.

Water as a solvent

Water dissolves many polar molecules and ions by gathering around substances that are polar or electrically charged.

Soluble

A substance is soluble in water if it dissolves in water.