Chemistry Atom Structure Unit review

atom

Basic unit of matter; made of protons, neutrons, and electrons.

nucleus

Central part of the atom containing protons and neutrons.

proton

Positively charged particle in the nucleus.

neutron

Neutral particle in the nucleus.

electron

Negatively charged particle found in the electron cloud.

atomic number

Number of protons in an atom; identifies the element.

mass number

Protons + neutrons.

isotope

Atoms of the same element with different numbers of neutrons.

ion

Atom with a charge due to gaining or losing electrons.

metals

Elements that are shiny, conductive, malleable.

nonmetals

Poor conductors, dull, brittle.

metalloids

Elements with properties of both metals and nonmetals.

alkali metals

Group 1, very reactive, form +1 ions.

alkaline earth metals

Group 2, reactive metals, form +2 ions.

transition metals

Center block of PT; variable charges; good conductors.

lanthanides

Shiny, reactive metals in f-block.

actinides

Radioactive elements, mostly synthetic.

halogens

Group 17, very reactive nonmetals, form –1 ions.

noble gases

Group 18, unreactive due to full valence shell.

period

Horizontal row on the periodic table.

group/family

Vertical column on the periodic table.

periodic law

Properties of elements repeat when arranged by atomic number.

atomic radius

Size of the atom; increases down, decreases across.

electronegativity

Ability to attract electrons; increases across, decreases down.

ionization energy

Energy needed to remove an electron; increases across, decreases down.

electron configuration

Arrangement of electrons in orbitals.

orbital

Region where an electron is likely to be found.

principal energy level

Main energy level of electrons (n = 1,2,3…).

sublevel

Different shapes (s, p, d, f) within an energy level.

Aufbau principle

Electrons fill lowest energy orbitals first.

Pauli Exclusion Principle

Each orbital holds 2 electrons with opposite spins.

Hund’s Rule

Electrons fill orbitals singly before pairing.

diagonal rule

Tool for determining electron filling order.

valence electrons

Outer-shell electrons involved in bonding.

representative elements

Elements in groups 1, 2, and 13–18.

nuclear charge

The positive charge of the nucleus (number of protons).

shielding effect

Inner electrons block attraction to outer electrons.

orbital box diagram

Diagram showing electrons as arrows in orbital boxes.

spectroscopic notation

Shorthand electron configuration (1s² 2s² 2p⁶…).

kernel method

Shortened configuration using noble gas notation.

spectroscope

Instrument used to observe atomic emission spectra.

inner transition metals

Lanthanides + actinides located in the f-block.

semi-metals

Same as metalloids; properties of both metal and nonmetal.