Atoms and Periodic Table Basics

Vocabulary flashcards covering key terms from the lecture notes on atoms, electrons, isotopes, ions, and the periodic table.

Atom

The basic unit of matter consisting of a nucleus (protons and neutrons) with electrons surrounding it.

Nucleus

The atom's center made of protons and neutrons.

Proton

A positively charged particle in the nucleus.

Neutron

An electrically neutral particle in the nucleus.

Electron

A negatively charged particle orbiting the nucleus in electron shells.

Element

A substance made of atoms that all have the same number of protons (same atomic number).

Atomic number

The number of protons in the nucleus; determines the element.

Atomic mass

The mass of protons plus neutrons in the nucleus.

Isotope

Atoms of the same element with different numbers of neutrons; many are unstable and radioactive.

Valence electrons

Electrons in the outermost shell that largely determine chemical behavior.

Electron shells

Concentric layers around the nucleus where electrons reside.

Periodic table

A table listing elements with names, symbols, atomic numbers, and approximate atomic masses.

Group

A column in the periodic table; elements in the same group have the same number of valence electrons (helium is an exception).

Period

A row in the periodic table; elements in the same period have the same number of electron shells.

Noble gas

An element with a full valence shell and very low reactivity.

Helium

A noble gas with only two electrons, grouped with noble gases despite not having eight.

Alkali metals

Group 1 metals (excluding hydrogen) with 1 valence electron; shiny, soft, and highly reactive.

Metals

Elements that are typically shiny, malleable, and good conductors; mainly on the left side of the periodic table.

Nonmetals

Elements on the right side of the periodic table, mostly gases or insulators.

Metalloids (semimetals)

Elements with properties between metals and nonmetals, located along the boundary.

Ion

A charged atom with a different number of electrons than protons.

Anion

A negatively charged ion.

Cation

A positively charged ion.

Molecule

Two or more atoms bonded together.

Compound

A substance formed when two or more different elements bond together.

Table salt (NaCl)

A common compound formed from sodium (an alkali metal) and chlorine.

Bonding

The process by which atoms join to form molecules and compounds; compounds can behave differently than the elements.

Left-right line (metals vs nonmetals)

A dividing line where metals lie to the left, nonmetals to the right; metalloids sit along the boundary.

Ionizing radiation

Radiation emitted by unstable isotopes as they decay; can be harmful.