Chemistry Atom Test & Electron Configurations

Pauli Exclusion Principle

A rule in quantum mechanics stating that no two electrons in an atom can occupy the same quantum state simultaneously. In simpler terms, if two electrons are in the same orbital, they must have opposite spins, often represented as \uparrow and \downarrow.

Hund’s Rule

Electrons fill each orbital in a subshell singly (one electron per orbital) before they start to pair up. All single electrons in these orbitals will have the same spin (e.g., all ↑↑) to keep the atom stable.

Aufbau Principle

The rule that electrons fill the lowest energy levels first before moving to higher ones. Think of it like filling a building from the ground floor up; electrons always take the 'cheapest' or lowest-energy seats available before moving to the next level.

Dmitri Mendeleev

Developed the periodic table

How is the periodic table arranged?

in order of atomic number or into periods (rows) and family groups (columns)

The way the periods are on the table:

horizontally (left to right)

The way the groups are on the table:

vertically (top to bottom)

Which groups are the most reactive elements located in?

Group 1

Which group has the least reactive elements?

Group 18

What are the three parts of an atom? List them smallest to largest.

electrons, protons, and neutrons

Charge of electrons

negative

Charge of protons

positive

Charge of neutrons

no charge or neutral

John Dalton

Developed the atomic theory

What experiment allowed us to see the behavior of electrons? Which scientist experimented?

Cathode Ray Tube experiment by J.J. Thomson.

Which experiment showed the presence of the atom? Which scientist experimented?

Gold Foil experiment by Ernest Rutherford.

J.J. Thomson

Developed the plum pudding model

What does the atomic number tell you about the atom?

the number of protons & electrons in an atom’s nucleus

How do you determine the number of electrons in an atom?

Subtract the # of protons from the atomic mass #

What does the n quantum number tell you?

What other facts can you determine from looking at quantum numbers?

What is the difference between electron configuration and orbital notation?

Electron configuration is a shorthand, numerical format showing how many electrons are in each energy sublevel while orbital notation is a detailed visual diagram showing the specific orbital, spin direction, and pairing of each electron