"A particle that consists of a nucleus of protons and neutrons surrounded by an electromagnetically-bound cloud of electrons."
This topic covers the structure of atoms, elements, and the periodic table, including atomic number, mass, electron configuration, and valence electrons.
Subatomic Particles: Discusses the three types of subatomic particles ─ protons, neutrons, and electrons ─ and their properties (e.g. mass, charge, location).
Atomic Number: Defines atomic number as the number of protons in an atom's nucleus and explains how it determines the element to which the atom belongs.
Isotopes: Describes isotopes as variants of the same element that differ in the number of neutrons in their nuclei and explains how isotopes are identified and named.
Mass Number: Defines mass number as the sum of the number of protons and neutrons in an atom's nucleus and distinguishes it from atomic mass.
Atomic Mass: Defines atomic mass as the weighted average mass of all the isotopes of an element and explains how it is calculated using isotopic abundances.
Electron Configuration: Explains how electrons are distributed in the different energy levels (or shells) around an atom's nucleus, and how to represent electron configuration using standard notation.
Orbitals: Introduces the concept of orbitals as regions of space around an atom's nucleus where electrons are most likely to be found, and distinguishes different types of orbitals (e.g. s, p, d, f).
Quantum Numbers: Describes the four quantum numbers (n, l, m, s) that specify the properties of an electron in an atom's orbital, and their significance.
Electron Spin: Introduces the concept of electron spin as an intrinsic property of electrons, which governs their behavior in magnetic fields and determines their contribution to atomic properties.
Periodic Table: Presents the periodic table as a systematic arrangement of elements according to their atomic number and electron configuration, and highlights its main features (e.g. periods, groups, blocks).
Dalton's Atomic Theory: Proposed by John Dalton in the early 19th century, it stated that atoms were indivisible and indestructible, and all atoms of the same element had identical properties.
Thomson's Plum Pudding Model: Proposed by J.J. Thomson in 1904, it proposed that the atom was a positively charged sphere with negatively charged electrons embedded in it, like raisins in a plum pudding.
Rutherford's Nuclear Model: Proposed by Ernest Rutherford in 1911, it proposed that the atom had a small, dense, positively charged nucleus orbited by electrons, like the sun and the planets in the solar system.
Bohr's Model: Proposed by Niels Bohr in 1913, it proposed that electrons orbited the nucleus in specific energy levels, and that energy was released or absorbed when electrons moved between these levels.
Quantum Mechanical Model: Proposed in the 1920s, it is the current accepted model of the atom. It proposes that electrons exist in orbitals, which are fuzzy regions of space where electrons are likely to be found, and that the behavior of electrons is described by the principles of quantum mechanics.
"The chemical elements are distinguished from each other by the number of protons that are in their atoms."
"The number of protons that are in their atoms."
"Any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper."
"The number of neutrons."
"Atoms are so small that accurately predicting their behavior using classical physics is not possible due to quantum effects."
"Typically around 100 picometers across."
"More than 99.94%."
"If the numbers of protons and electrons are equal, as they normally are, then the atom is electrically neutral."
"If it has more protons than electrons, it has a positive charge, and is called a positive ion (or cation)."
"If an atom has more electrons than protons, then it has an overall negative charge, and is called a negative ion (or anion)."
"The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force." "The protons and neutrons in the nucleus are attracted to each other by the nuclear force."
"The nuclear force is usually stronger than the electromagnetic force."
"When the repelling electromagnetic force becomes stronger than the nuclear force."
"The nucleus splits and leaves behind different elements."
"Chemical bonds to form chemical compounds such as molecules or crystals."
"The ability of atoms to attach and detach from each other."
"Chemistry is the discipline that studies these changes."
"A nucleus of protons and neutrons."
"If any are present, have no electric charge."