Chemistry: Matter, Elements & Atomic Structure

Vocabulary flashcards covering key terms and groups related to matter, elements, the periodic table, and atomic structure from the lecture notes.

Matter

Anything that occupies space and has mass; the “stuff” of the universe.

Element

A substance with unique chemical and physical properties that cannot be broken down into simpler substances through ordinary chemical reactions.

Essential Biological Elements (O, C, H, N)

Oxygen, carbon, hydrogen, and nitrogen—four elements that constitute about 96 % of the human body.

Periodic Table

Tabular arrangement of the 118 known elements (92 naturally occurring) based on atomic number and recurring chemical properties.

Alkali Metals (Group IA)

Soft, shiny, highly reactive metals with one loosely bound valence electron; can explode on contact with water (e.g., cesium, francium).

Alkaline Earth Metals (Group IIA)

Less reactive than alkali metals; contain two valence electrons, readily form +2 cations, and have smaller atomic radii than alkali metals.

Transition Metals

Fairly unreactive, malleable metals with high melting/boiling points, good electrical conductivity, low ionization energies, and multiple oxidation states.

Halogens

Extremely reactive non-metals with very high electronegativities; form −1 anions and react vigorously with alkali and alkaline earth metals.

Noble Gases

Group of completely unreactive gases with full valence shells, very low electronegativities, low boiling points, and gaseous state at room temperature.

Lanthanides

Elements 58–71; silvery-white, highly reactive metals that tarnish in air, possess high melting/boiling points, and act as strong reducing agents.

Actinides

Elements 90–103; dense, highly electropositive, all radioactive metals that readily combine with most non-metals.

Metals

Elements that are typically solid at room temperature (except mercury), malleable, ductile, and good conductors of heat and electricity.

Metalloids

Elements with properties intermediate between metals and non-metals, often semiconductors.

Non-metals

Elements that are generally brittle solids or gases, poor conductors, and tend to gain electrons easily.

Atom

Smallest unit of matter that retains the properties of an element; composed of a nucleus surrounded by electrons.

Nucleus

Central region of an atom containing positively charged protons and neutral neutrons.

Proton

Positively charged subatomic particle located in the nucleus; the number of protons defines an element (atomic number).

Neutron

Neutral subatomic particle in the nucleus; hydrogen typically lacks neutrons.

Electron

Negatively charged subatomic particle orbiting the nucleus; its arrangement influences an atom’s chemical behavior.

Valence Electron

Electron in the outermost shell of an atom involved in chemical bonding; alkali metals have one, alkaline earth metals have two.

Cation

Positively charged ion formed when an atom loses one or more electrons (e.g., +2 ions from alkaline earth metals).

Anion

Negatively charged ion produced when an atom gains one or more electrons (e.g., −1 ions formed by halogens).

Ionization Energy

Energy required to remove an electron from an atom; transition metals possess relatively low ionization energies.

Brownian Motion

Random movement of particles (e.g., pollen) suspended in a fluid; explained mathematically by Einstein and evidencing atomic/molecular existence.