anion
a negative ion formed by gaining electrons
Negative ions are formed by gaining electrons and are called anions.
atomic number
the number of protons in an atom
Each contains a different number of protons and neutrons, giving it its own atomic number and mass number.
cation
a positive ion formed by losing electrons
Positive ions are formed by losing electrons and are called cations.
chemical bond
an interaction between two or more of the same or different elements that results in the formation of molecules
Another type of strong chemical bond between two or more atoms is a covalent bond.
covalent bond
a type of strong bond between two or more of the same or different elements; forms when electrons are shared between elements
Another type of strong chemical bond between two or more atoms is a covalent bond.
electron
a negatively charged particle that resides outside of the nucleus in the electron orbital; lacks functional mass and has a charge of –1
All atoms contain protons, electrons, and neutrons.
electron transfer
the movement of electrons from one element to another
This movement of electrons from one element to another is referred to as electron transfer.
element
one of 118 unique substances that cannot be broken down into smaller substances and retain the characteristic of that substance; each element has a specified number of protons and unique properties
The elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus are the key building blocks of the chemicals found in living things.
hydrogen bond
a weak bond between partially positively charged hydrogen atoms and partially negatively charged elements or molecules
Two weak bonds that occur frequently are hydrogen bonds and van der Waals interactions.
ion
an atom or compound that does not contain equal numbers of protons and electrons, and therefore has a net charge
When an atom does not contain equal numbers of protons and electrons, it is called an ion.
ionic bond
a chemical bond that forms between ions of opposite charges
Unlike ionic bonds, covalent bonds do not dissociate in water.
isotope
one or more forms of an element that have different numbers of neutrons
Isotopes are different forms of the same element that have the same number of protons, but a different number of neutrons.
mass number
the number of protons plus neutrons in an atom
Each contains a different number of protons and neutrons, giving it its own atomic number and mass number.
matter
anything that has mass and occupies space
Food provides an organism with nutrients—the matter it needs to survive.
neutron
a particle with no charge that resides in the nucleus of an atom; has a mass of 1
All atoms contain protons, electrons, and neutrons.
nonpolar covalent bond
a type of covalent bond that forms between atoms when electrons are shared equally between atoms, resulting in no regions with partial charges as in polar covalent bonds
Nonpolar covalent bonds form between two atoms of the same element or between different elements that share the electrons equally.
nucleus
(chemistry) the dense center of an atom made up of protons and (except in the case of a hydrogen atom) neutrons
A proton is a positively charged particle that resides in the nucleus (the core of the atom) of an atom and has a mass of 1 and a charge of +1.
octet rule
states that the outermost shell of an element with a low atomic number can hold eight electrons
Because the outermost shells of the elements with low atomic numbers (up to calcium, with atomic number 20) can hold eight electrons, this is referred to as the octet rule.
periodic table of elements
an organizational chart of elements, indicating the atomic number and mass number of each element; also provides key information about the properties of elements
Because of these characteristics, the elements are arranged into the periodic table of elements, a chart of the elements that includes the atomic number and relative atomic mass of each element.
polar covalent bond
a type of covalent bond in which electrons are pulled toward one atom and away from another, resulting in slightly positive and slightly negative charged regions of the molecule
In a polar covalent bond, the electrons shared by the atoms spend more time closer to one nucleus than to the other nucleus.
proton
a positively charged particle that resides in the nucleus of an atom; has a mass of 1 and a charge of +1
Each element is made of atoms, each with a constant number of protons and unique properties.
radioactive isotope
an isotope that spontaneously emits particles or energy to form a more stable element
These are called radioactive isotopes or radioisotopes.
van der Waals interaction
a weak attraction or interaction between molecules caused by slightly positively charged or slightly negatively charged atoms
Two weak bonds that occur frequently are hydrogen bonds and van der Waals interactions.
acid
a substance that donates hydrogen ions and therefore lowers pH
Acids are substances that provide hydrogen ions (H+) and lower pH, whereas bases provide hydroxide ions (OH–) and raise pH.
adhesion
the attraction between water molecules and molecules of a different substance
These cohesive forces are also related to the water’s property of adhesion, or the attraction between water molecules and other molecules.
base
a substance that absorbs hydrogen ions and therefore raises pH
Acids are substances that provide hydrogen ions (H+) and lower pH, whereas bases provide hydroxide ions (OH–) and raise pH.
buffer
a solution that resists a change in pH by absorbing or releasing hydrogen or hydroxide ions
Buffers readily absorb excess H+ or OH–, keeping the pH of the body carefully maintained in the aforementioned narrow range.
cohesion
the intermolecular forces between water molecules caused by the polar nature of water; creates surface tension
This water can stay above the glass because of the property of cohesion.
evaporation
the release of water molecules from liquid water to form water vapor
Evaporation of sweat, which is 90 percent water, allows for cooling of an organism, because breaking hydrogen bonds requires an input of energy and takes heat away from the body.
hydrophilic
describes a substance that dissolves in water; water-loving
When a substance readily forms hydrogen bonds with water, it can dissolve in water and is referred to as hydrophilic (“water-loving”).
hydrophobic
describes a substance that does not dissolve in water; water-fearing
These nonpolar compounds are hydrophobic (“water-fearing”) and will not dissolve in water.
litmus paper
filter paper that has been treated with a natural water-soluble dye so it can be used as a pH indicator
You have probably used litmus paper, paper that has been treated with a natural water-soluble dye so it can be used as a pH indicator, to test how much acid or base (alkalinity) exists in a solution.
pH scale
a scale ranging from 0 to 14 that measures the approximate concentration of hydrogen ions of a substance
The overall concentration of hydrogen ions is inversely related to its pH and can be measured on the pH scale (Figure 2.11).
solvent
a substance capable of dissolving another substance
Water is, therefore, what is referred to as a solvent—a substance capable of dissolving another substance.
surface tension
the cohesive force at the surface of a body of liquid that prevents the molecules from separating
Cohesion gives rise to surface tension, the capacity of a substance to withstand rupture when placed under tension or stress.
temperature
a measure of molecular motion
For example, one hydrogen atom has all of the properties of the element hydrogen, such as it exists as a gas at room temperature, and it bonds with oxygen to create a water molecule.
amino acid
a monomer of a protein
They are all, however, polymers of amino acids, arranged in a linear sequence.
carbohydrate
a biological macromolecule in which the ratio of carbon to hydrogen to oxygen is 1:2:1; carbohydrates serve as energy sources and structural support in cells
They form the carbohydrates, nucleic acids, proteins, and lipids (all of which will be defined later in this chapter) that are the fundamental molecular components of all organisms.
cellulose
a polysaccharide that makes up the cell walls of plants and provides structural support to the cell
Starch, glycogen, cellulose, and chitin are examples of polysaccharides.
chitin
a type of carbohydrate that forms the outer skeleton of arthropods, such as insects and crustaceans, and the cell walls of fungi
Starch, glycogen, cellulose, and chitin are examples of polysaccharides.
denaturation
the loss of shape in a protein as a result of changes in temperature, pH, or exposure to chemicals
Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to a loss of function or denaturation (to be discussed in more detail later).
deoxyribonucleic acid (DNA)
a double-stranded polymer of nucleotides that carries the hereditary information of the cell
These bonds give rise to the unique properties of water and the unique structures of DNA and proteins.
disaccharide
two sugar monomers that are linked together by a peptide bond
Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.
enzyme
a catalyst in a biochemical reaction that is usually a complex or conjugated protein
In these animals, certain species of bacteria reside in the rumen (part of the digestive system of herbivores) and secrete the enzyme cellulase.
fat
a lipid molecule composed of three fatty acids and a glycerol (triglyceride) that typically exists in a solid form at room temperature
Hydrogen bonds are not readily formed with nonpolar substances like oils and fats .
glycogen
a storage carbohydrate in animals
Starch, glycogen, cellulose, and chitin are examples of polysaccharides.
hormone
a chemical signaling molecule, usually a protein or steroid, secreted by an endocrine gland or group of endocrine cells; acts to control or regulate specific physiological processes
Lipids are also the building blocks of many hormones and are an important constituent of the plasma membrane.
lipids
a class of macromolecules that are nonpolar and insoluble in water
They form the carbohydrates, nucleic acids, proteins, and lipids (all of which will be defined later in this chapter) that are the fundamental molecular components of all organisms.
macromolecule
a large molecule, often formed by polymerization of smaller monomers
These interactions determine what atoms combine and the ultimate shape of the molecules and macromolecules, that shape will determine their function.
monosaccharide
a single unit or monomer of carbohydrates
Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.
nucleic acid
a biological macromolecule that carries the genetic information of a cell and carries instructions for the functioning of the cell
They form the carbohydrates, nucleic acids, proteins, and lipids (all of which will be defined later in this chapter) that are the fundamental molecular components of all organisms.
nucleotide
a monomer of nucleic acids; contains a pentose sugar, a phosphate group, and a nitrogenous base
DNA and RNA are made up of monomers known as nucleotides.
oil
an unsaturated fat that is a liquid at room temperature
Hydrogen bonds are not readily formed with nonpolar substances like oils and fats .
unsaturated fatty acid
a long-chain hydrocarbon that has one or more than one double bonds in the hydrocarbon chain
When the hydrocarbon chain contains a double bond, the fatty acid is an unsaturated fatty acid.
These terms were extracted from Concepts of Biology – 1st Canadian Edition by Charles Molnar and Jane Gair, eCampusOntario (originally published by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License. Chapter content adapted from Concepts of Biology by OpenStax (© Rice University), licensed under CC BY 4.0.