Chemistry Atom

Democritus

“all matter consists of very small indivisible particles called atoms”. He proposed this idea in ancient Greece.

John Dalton

he proposed that elements are composed of atoms, which are indivisible and identical for each element.

John Dalton

he proposed that compounds are composed of atoms of different elements, which combine in fixed ratios.

Joseph Proust

developed the law of definite proportions,

Law of definite proportion

states that a chemical compound always contains its component elements in fixed ratio by mass.

Law of multiple proportion

if two elements can combine to form more than one compound, the ratios of the masses of one element that combine with a fixed mass of the other are ratios of small whole numbers.

John Dalton

he proposed that a chemical reaction only involves separation, combination, or rearrangement of atoms without any change to the atoms themselves.

Antoine Lavoisier

French chemist known as the "father of modern chemistry," who established the Law of Conservation of Mass,

Law of conservation of mass

matter can be neither created nor destroyed

Solid sphere model

a model proposed by John Dalton suggesting that atoms are solid, indivisible spheres that combine in simple whole-number ratios.

Plum pudding model

a model developed by J.J. Thomson indicating that atoms consist of a positively charged "soup" with negatively charged electrons embedded within.

Nuclear model

a model introduced by Ernest Rutherford that describes the atom as having a small, dense nucleus surrounded by orbiting electrons.

Planetary model

a model proposed by Niels Bohr that describes electrons orbiting the nucleus in fixed paths, similar to planets orbiting the sun.

Quantum model

a physicist who developed the quantum mechanical model of the atom, which describes electrons as wave functions rather than fixed orbits.

electron

a negatively charged particle

proton

a positively charged subatomic particle found in the nucleus of an atom.

neutron

a neutral subatomic particle found in the nucleus of an atom.

atomic number (z)

equal to the number of protons present, also a defining characteristic

mass number

sum of neutron + protons

charge

difference between the number of protons and electrons in an atom.

percent natural abundance

relative abundance of a certain isotope compared to the total amount of isotopes of that element in nature.

atomic weight

the weighted average mass of an element's isotopes

isotope

elements with identical atomic number but different mass numbers due to varying numbers of neutrons.

isotone

elements with the same mass number but different atomic numbers.

isoelectronic

elements with same number of electrons

isobars

elements with the same mass number but different atomic numbers, resulting in different elements.

aufbau’s rule

A principle in chemistry that states electrons fill atomic orbitals in order of increasing energy levels, starting from the lowest energy first.

hund’s rule

states that electrons must occupy degenerate orbitals singly before pairing occurs, maximizing total spin.

pauli’s exclusion principle

no two electrons in an atom can have the same set of four quantum numbers, meaning each electron must differ in at least one quantum number.

principal (n)

A quantum number that defines the energy level of an electron in an atom, indicating the distance from the nucleus.

azimuthal (ℓ)

it describes the shape of a given orbital

magnetic (m_ℓ)

determines the total number of orbitals in a given subshell based on the value of the azimuthal quantum number.

magnetic spin (m_s)

it gives insight into the direction in which the electron is spinning

2

quantum number of (n)

1

azimuthal quantum number of the orbital

-1

quantum number for an orbital of magnetic

-1/2

magnetic spin’s quantum number, indicating one of the two possible spin states of an electron.