Chemistry Notes: Atomic Structure, Isotopes, Ions, Electron Configuration, and Periodic Trends

Matter

Anything that has mass and takes up space; it is composed of atoms.

Atoms

The fundamental building blocks of matter, composed of protons, neutrons, and electrons.

Protons

Positively charged fundamental particles located in the nucleus of an atom.

Neutrons

Neutral (no charge) fundamental particles located in the nucleus of an atom.

Electrons

Negatively charged fundamental particles that reside in electron shells/orbitals surrounding the nucleus.

Ions

Atoms that have gained or lost electrons, resulting in a net electrical charge.

Atomic number (Z)

The number of protons in the nucleus of an atom, which uniquely identifies an element.

Mass number (A)

The total number of protons and neutrons in the nucleus of an atom, calculated as A = Z + N.

Isotopes

Atoms of the same element (same Z) but with different numbers of neutrons (different A).

Monatomic ion

An ion formed from a single atom (e.g., Na

^+).

Polyatomic ion

An ion formed from two or more atoms chemically bonded together (e.g., SO

_4^{2

-}).

Cation

A positively charged ion.

Anion

A negatively charged ion.

Periods (Periodic Table)

The horizontal rows on the periodic table, indicating the principal energy level of the outermost electrons.

Groups (Periodic Table)

The vertical columns on the periodic table, where elements share similar chemical properties due to having the same number of valence electrons.

Atomic radius

A measure of the size of an atom; it increases down a group and decreases across a period from left to right.

Ionization energy

The energy required to remove the outermost electron from an atom; it generally increases up and to the right on the periodic table.

Electron configuration

The arrangement of electrons in an atom's shells and subshells, following a specific filling order to minimize energy.

s subshell capacity

The maximum number of electrons an s subshell can hold, which is 2 electrons.

p subshell capacity

The maximum number of electrons a p subshell can hold, which is 6 electrons.

d subshell capacity

The maximum number of electrons a d subshell can hold, which is 10 electrons.

Homogeneous mixture (solution)

A mixture with a uniform composition throughout, where its components are not visibly distinguishable.

Heterogeneous mixture

A mixture with visibly different parts or phases, indicating non-uniform composition.

Density

A physical property defined as the mass of a substance per unit volume, given by the formula ho = \frac{m}{V}.

LD50 (Lethal Dose 50)

The amount of a substance that is lethal to 50% of a test population, typically reported in mg per kg of body mass.

Significant figures

Digits in a measurement that carry meaning contributing to its precision

Atom

The basic unit of matter, composed of protons, neutrons, and electrons.

Proton

A fundamental particle in an atom's nucleus with a positive charge.

Neutron

A fundamental particle in an atom's nucleus with no charge.

Electron

A fundamental particle orbiting the nucleus with a negative charge.

Ion

An atom or molecule that has gained or lost electrons, resulting in a net electrical charge.

Atomic Number (Z)

The number of protons in an atom's nucleus, which defines the identity of the element.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus (A = Z + N).

Isotopes

Atoms of the same element (same Z) but with different numbers of neutrons (different A).

Cation

A positively charged ion.

Anion

A negatively charged ion.

Monatomic Ion

An ion made from a single atom (e.g., Na^+).

Polyatomic Ion

An ion made from two or more atoms (e.g., SO_4^{2-}).

Periods (Periodic Table)

Horizontal rows on the periodic table.

Groups (Periodic Table)

Vertical columns on the periodic table.

Atomic Radius

The size of an atom. It increases down a group and decreases across a period from left to right.

Ionization Energy

The energy required to remove the outermost electron from an atom.

Electron Configuration

The distribution of electrons of an atom or molecule in atomic or molecular orbitals.

s subshell capacity

Holds up to 2 electrons.

p subshell capacity

Holds up to 6 electrons.

d subshell capacity

Holds up to 10 electrons.

Noble Gas Core

A shorthand notation in electron configuration that represents the electron configuration of the nearest noble gas.

Homogeneous Mixture (Solution)

A mixture with uniform composition where individual parts cannot be visibly distinguished.

Heterogeneous Mixture

A mixture with visibly different parts and non-uniform composition.

Density (\rho)

A physical property defined as mass per unit volume (\rho = \frac{m}{V}).

LD50 (Lethal Dose 50)

The amount of a substance that will kill 50% of a test population, typically reported as mg/kg.

Significant Figures

Digits in a number that are considered reliable and convey precision in a measurement.