chem

Subatomic Particles (Charge & Mass)

• Proton: Charge = 1+, Relative Mass = 1

• Neutron: Charge = 0, Relative Mass = 1

• Electron: Charge = 1-, Relative Mass = 1/1836

What is an isotope?

Atoms of the same element with the same number of protons, but different numbers of neutrons.

What is an ion?

Charged particles formed when atoms lose or gain electrons.

Positive ions: Have lost electrons.

Negative ions: Have gained electrons.

What is relative mass compared against?

1/12th of the mass of an atom of carbon-12.

Electron Shells & Subshells

Shells split into s, p, and d subshells (which correspond to blocks on the periodic table):

• 1st shell: 1s

• 2nd shell: 2s, 2p

• 3rd shell: 3s, 3p

• 4th shell: 4s, 3d, 4p

Subshell Capacities (Orbitals & Max Electrons)

• s-subshell: 1 orbital | Max 2 electrons

• p-subshell: 3 orbitals | Max 6 electrons

• d-subshell: 5 orbitals | Max 10 electrons

Shapes of s and p Orbitals

• s-orbitals: Spherical in shape.

• p-orbitals: Dumbbell-shaped (there are 3 p-orbitals in a p-subshell).

Core Rules for Filling Electronic Configurations

• Electrons fill the lowest energy subshells first.

• Electrons occupy orbitals singly before pairing up.

• The 4s subshell fills before 3d.

Chromium (Cr) & Copper (Cu) Exceptions

They have half-filled or fully filled d-subshells for extra stability:

• Chromium (Cr): Ends in 4s¹ 3d⁵

• Copper (Cu): Ends in 4s¹ 3d¹⁰

Ion Formation Rules (Electron Loss/Gain)

• Electrons are lost or gained from the highest energy level.

• Exception: Transition metals lose electrons from 4s before 3d.

define a mole

used to measure the amount of a substance

2 formula for mole

amount (moles) = number of particles / Avogadro constant (6.02 x10²³)

amount (moles) = mass (g)/relative formula mass (gmol^-1)