IB Chemistry Atoms and electrons 2025

Define first Ionization energy

the energy required to remove one electron from each atom in one mole of gaseous atoms under standard conditions

Define Second Ionization energy

the energy required to remove one electron from one mole of gaseous 1+ ions under standard conditions

equation for first ionization energy of magnesium

M(g) → M⁺(g)+e⁻

equation for second ionization of magnesium

M ⁺(g) → M²⁺(g)+e⁻

Why is second ionization energy always higher than the first?

positive ions attract electrons more strongly than neutral atoms there is less repulsion between remaining electron after an electron has been removed (stronger attraction to the nucleus)

What is shielding?

decrease in attraction between a (valence) electron and the nucleus due to repulsion from inner electrons

Effect of more shielding

decrease in ionization energy as there is less attraction between the valence electrons and the nucleus

Effective nuclear charge

the net attractive positive charge of nuclear protons acting on valence electrons

Effect of higher effective nuclear charge

increase in ionization energy as there is greater attraction between the nucleus and the valence electrons

Sketch the graph of the successive ionization energies (IE) of Potassium

What is the equation for photon energy (E)

E=hv from h (Planck's constant) and f (frequency of the light in the emission spectrum)

How does ionization energy vary across a period

it generally increases as there is a larger effective nuclear charge felt by electrons in the same shell.

How does ionization energy vary across a group

it decreases as atomic radius increases and thus attraction between the nucleus and the valence electrons decreases.

equation for wavelength (λ)

λ=c /f from the speed of light (c) divided by frequency (f)

Explain why the third ionization energy of magnesium (Mg) is much greater than the second ionization energy

The electron is in lower energy level, so the electron shell is more stable OR The electron closer to nucleus, so there is an increase in effective nuclear charge. AND less shielding as fewer shells

Why is there a drop in ionisation energy between group 15 and 16?

Electron pair repulsion due to electrons sharing a p orbital

Why is there a drop in ionisation energy from Be to B?

The highest energy electron in B is in a p orbital which is at a higher energy level than the s orbital

The ionisation energy is the energy transition between an electron and ....

the convergence limit (n=∞)

Electronegativity

a measure of the tendency of an atom to attract a bonding pair of electrons

electron affinity

the energy change that occurs when an electron is acquired by a neutral atom

Periodicity

the repeating pattern of chemical and physical properties of the elements

line spectrum

a spectrum showing only certain discrete wavelengths

continuous spectrum

an emission spectrum that consists of a continuum of wavelengths.

Isotope

Atoms of the same element that have different numbers of neutrons

Emission spectra are produced by

atoms emitting photons when electrons in excited states return to lower energy levels.

A transition in the hydrogen atom to n = 3 produces

Infrared light

A transition in the hydrogen atom to n = 2 produces

visible light

A transition in the hydrogen atom to n = 1 produces

Ultra violet light

The main energy level is given an integer number, n, and can hold a maximum of

2n² electrons

Shape of an s orbital

spherical

shape of p orbital

dumbbell

group 1

Alkali metals

Group 17

Halogens

Group 0

noble gases

Define oxidation

oxygen gain/hydrogen loss, electron loss or increase in oxidation number.

Which elements have variable oxidation state

transition metals and most main-group non-metals.

Oxidation state of elements

0

Oxidation state of fluorine

-1 in its compounds

oxidation state of oxygen

-2 except in peroxides where it is -1

oxidation state of chlorine

-1 (except in compounds with F and O, where it has positive values)

oxidation state of hydrogen

Always +1 except in metal hydrides where it's -1

oxidation state of group 1

+1

oxidation state of group 2

+2

oxidation state of group 13

+3

The sum of the oxidation states in a species =

the charge of the species (0 in molecules)

Half equations show

either oxidation or reduction

In a reaction a reducing agent will be

oxidised

In a reaction an oxidising agent will be

reduced

which is correct for showing oxidation number 2+ or +2

+2

What does the (VI) in potassium dichromate (VI) tell us about the compound

The oxidation number (+6) of chromium

Oxidising agent

The reactant that is reduced (gains electrons)

reducing agent

The reactant that is oxidized (loses electrons)

electronic configuration of copper

1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰

electronic configuration of chromium

1s²2s²2p⁶3s²3p⁶4s¹3d⁵

Aufbau principle

electrons fill subshells of the lowest available energy, then they fill subshells of higher energy.

Hund's Rule

when an elecron is added to a subshell, it will always occupy an empty orbital if one is available

Pauli Exclusion Principle

The rule that an orbital can hold only two electrons with opposite spin

Relative atomic mass

The weighted average mass of an atom relative to relative to 1/12 of a carbon-12 atom

Relative formula mass

The weighted average mass of the formula of a compound relative to relative to 1/12 of a carbon-12 atom

Relative isotopic mass

The mass of an atom of an isotope on a scale where the mass of an atom relative to 1/12 of a carbon-12 atom

In an emission spectrum, the limit of convergence at higher frequency corresponds to

ionization energy

What does hot gas give?

Hot gas causes emission spectrum because it excites electrons. (electron emits photon when deexcited)

What does cold gas give?

Cold gas gives absorption spectrum (electron absorbs EM wave so it is not detected)