Concept 2.2: An element's properties depend on the structure of its atoms

Flashcards from Concept 2.2 of Pearson's Campbell Biology, Twelfth Edition.

Atom

The smallest unit of matter that still retains the properties of an element

Subatomic particles

The particles that compose atoms, including:

• Neutrons (no electrical charge)

• Protons (positive electrical charge)

• Electrons (negative electrical charge)

Atomic nucleus

The center of an atom formed by neutrons and protons surrounded by a “cloud” of negative charge by electrons

Daltons

The unit of mass when measuring subatomic particles like neutrons and protons; electron masses are so small that they are ignored when calculating atomic masses

Atomic number

The number of protons in an atom’s nucleus

Mass number

The sum of the masses of the protons and neutrons in the nucleus

Atomic mass

The atom’s total mass which is usually approximated by the mass number

Isotopes

Two atoms of an element that differ in the number of neutrons (neutral particles)

Radioactive isotopes

Isotopes that decay spontaneously and give off particles and energy; they are often used as diagnostic tools in medicine for metabolic function and internal imaging

Half-life

The rate of decay for an isotope to turn into another more stable isotope; can vary from seconds or days to billions of years

Radiometric dating

Measurement of the ratio of different isotopes in a material to calculate how many half-lives have passed since formation

Energy

The capacity to cause change

Potential energy

The energy that matter possesses because of its location or structure; matter has a tendency to move to the lowest possible state of this

Electron shells

Where electrons are found with a different average distance and energy level at fixed distances due to differences in potential energy

Chemical behavior

Defined by the distribution of electrons in electron shells shown by the periodic table of elements

• The left-to-right sequence of elements in each row corresponds to additional electrons and protons

Valence electrons

Electrons in the outermost electron shell that determine an element’s chemical behavior; elements with a full shell of these are chemically inert

Electron orbital

The three-dimensional space where an electron is found 90% of the time; each electron shell consists of a specific number of these with no more than 2 electrons in each