Chem unit 3 electrons

Oxidation number

A number assigned to an atom to represent how many electrons are lost or gained.

Electrostatic Attraction

Attraction between charged particles; electrons are attracted to protons.

Electron Shielding

Inner electrons shield outer electrons from the full nuclear charge.

Atomic Radius

Size of an atom; decreases across a period and increases down a group.

Ionization Energy

Energy required to remove an electron; increases across a period and decreases down a group.

Electronegativity

Ability to attract electrons; increases across a period and decreases down a group.

Ionic Radius

Size of an ion; cations are smaller due to loss of electrons, while anions are larger due to gain of electrons.

Cations

Positively charged ions formed by loss of electrons, resulting in a smaller ionic radius.

Anions

Negatively charged ions formed by gain of electrons, resulting in a larger ionic radius.

Hund's rule

Electrons fill orbitals singly before pairing up.

Pauli Exclusion Principle

Electrons in the same orbital must have opposite spins.

Aufbau Principle

Electrons fill lower energy levels before filling higher levels.

Excitation of electrons

Occurs when electrons move to a higher energy level.

Spectrum

All forms of electromagnetic radiation.

Ionizing radiation

Radiation with enough energy to remove an electron from an atom.

Non-ionizing radiation

Radiation not having enough energy to remove an electron; the atom remains stable.

Why does atomic radius decrease across a period?

As you move across a period, more protons are added to the nucleus, increasing electrostatic attraction between the nucleus and electrons. This pulls electrons closer, making the atom smaller.

Why does ionization energy increase across a period?

Since atoms have more protons across a period, they have a stronger pull on their electrons. This makes it harder to remove an electron, so more energy is required (higher ionization energy).

Why does atomic radius increase down a group?

As you move down a group, atoms gain more energy levels (electron shells). Even though the nucleus has more protons, the extra electron shells increase electron shielding, weakening the pull on outer electrons and making the atom larger.

Why does ionization energy decrease down a group?

Moving down a group, atoms have more electron shielding, which weakens the nuclear pull on outer electrons. Since the nucleus holds electrons less tightly, less energy is required to remove an electron, so ionization energy decreases.

Why does electronegativity increase across a period?

Across a period, atoms gain more protons but don’t get much extra shielding. This stronger nuclear attraction pulls electrons in closer and makes atoms more eager to attract additional electrons in bonds, so electronegativity increases.

Why does electronegativity decrease down a group?

As you move down a group, more electron shielding weakens the pull of the nucleus on bonding electrons. Since the nucleus has less ability to attract shared electrons, electronegativity decreases.