Chapter 2 RX - What Did You Learn? 2.1 Chemical Elements and 2.2 Molecules and Compounds

Vocabulary-style flashcards covering the key terms and definitions from 2.1 Chemical Elements and 2.2 Molecules and Compounds.

Matter

Substance that makes up living and nonliving things; composed of elements.

Elements

Substances composed of a single type of atom; essential elements in living organisms include carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

CHNOPS

The six most significant elements in living organisms: carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur.

Atomic symbol

A unique abbreviation for an element (e.g., Na for sodium).

Atom

The basic unit of a chemical element, consisting of protons, neutrons, and electrons.

Proton

Positively charged subatomic particle in the nucleus.

Neutron

Electrically neutral subatomic particle in the nucleus.

Electron

Negatively charged subatomic particle orbiting the nucleus in electron shells.

Nucleus

Center of the atom containing protons and neutrons.

Mass number

Total number of protons and neutrons in the nucleus.

Atomic number

Number of protons in the nucleus; equals the number of electrons in a neutral atom.

Isotope

Atoms of the same element with different numbers of neutrons, leading to different atomic masses.

Radioactive isotope

Isotopes with unstable nuclei used as tracers in biology and medicine.

Atomic mass

Average mass of an element's naturally occurring isotopes.

Electron shell / energy level

Discrete distances from the nucleus where electrons reside.

Valence shell

Outermost electron shell; its electron count determines an atom's reactivity.

First shell

Innermost shell; complete with two electrons.

Octet rule

Atoms react to achieve a full valence shell of eight electrons.

Calcium (Ca)

Element with atomic number 20; used as a reference for stable outer shells beyond the first.

Electron shell capacity

First shell holds 2 electrons; subsequent shells tend to hold 8 electrons to be stable (octet rule) up to calcium.

Reactivity

Tendency of atoms to react with other atoms to achieve a stable octet.

Molecules

Two or more atoms held together by chemical bonds.

Compounds

Substances composed of two or more elements in fixed ratios.