Intuition The one core ideaAn alkali metal is an atom carrying one loose outer electron that it is desperate to give away, and almost every property in the parent note is just the story of how tightly (or loosely) the nucleus grips that one electron. Once you can picture the tug-of-war between the positive nucleus pulling inward and the distance/shielding pushing that grip weaker, every trend — radius, ionization energy, melting point, reactivity — falls out of the same picture.
This page builds every symbol and idea the parent note used, from the ground up. Read it top to bottom; each block depends only on the ones before it.
Before any symbol, fix the picture in your head.
An atom is a tiny positive core (the nucleus , made of protons and neutrons) surrounded by electrons living in shells — think of them as roughly circular "lanes" at increasing distance from the centre. Look at the figure: the innermost lane is closest and lowest energy, and each lane further out is a bigger circle.
A shell is one of the allowed distance-lanes an electron can occupy. Shells are counted outward and given letters: the 1st is K , the 2nd L , the 3rd M , the 4th N , … The further out, the higher the energy and the weaker the nucleus's pull on an electron there.
Definition Valence electronThe valence electron(s) are the electrons in the outermost occupied shell — the ones on the very edge of the atom (magenta electron in the figure). For an alkali metal there is exactly one , and it is the star of this whole topic.
Why the topic needs this: every alkali-metal property is about that one outer electron — how far out it sits and how easily it leaves.
The parent note writes things like "Li: [He] 2s¹". Let us earn every piece.
Definition Orbital letters s, p, dInside a shell, electrons sit in sub-lanes called orbitals , labelled by letters s , p , d , … s s 2 electrons.
The number in front (the 2 in 2 s shell number — which lane.
The letter (s ) is the orbital shape.
The tiny raised number (the ¹ in s 1 superscript ) is how many electrons sit there.
So 2 s 1 one electron."
Definition Noble-gas shorthand [He], [Ne], …[ He ] [ He ] 2 s 1 a stable helium core, plus one lonely electron in shell 2. It is just a space-saver so we can focus on the valence electron.
Now the tug-of-war. Four symbols appear all through the parent note. Here is each, as a picture.
Definition Nuclear chargeZ == Z == positive pull at the centre. Bigger Z
σ between the nucleus and the outer electron, partly blocking the pull — like people standing in front of a magnet. That blocking is the ==shielding constant σ sigma ). More inner electrons ⇒ bigger σ
Definition Effective nuclear chargeZ eff actually feels after shielding is
Z eff = Z − σ . (total positive pull) minus (how much the inner crowd blocks it). This is the net grip on the valence electron — the single most important quantity in the topic.
r == r == 1/ r 2 r
Intuition The master trade-off (memorise this feeling)Going down the group Li → Cs: Z r σ Distance wins. So the grip on the outer electron gets weaker downward — that one sentence explains falling ionization energy, rising radius, falling melting point, and rising reactivity all at once. See 3.106-Periodic-trends-in-s-block .
Z eff Z Z eff not just the atomic number. A big Z σ
Definition Cation and the M⁺ symbolWhen the atom loses its outer electron it becomes positively charged — a cation , written M + M +
Definition The state label (g), (s), (aq)A symbol in brackets after a species tells you its physical state: ( s ) ( g ) ( a q )
The oxygen-reaction section rests on lattice energy . Build it.
Definition Anion and charge symbolsz + z − anion is a negatively charged ion (gained electrons), e.g. oxide O 2 − z + z + = 1 z − z − = 2
When cations and anions stack in a repeating 3-D grid, that grid is a lattice . The energy released when the free gas ions snap into the grid is the lattice energy U stable/tightly bound the solid is.
The parent note's surprise — Li is the strongest reducing agent despite the highest I.E. — needs three energy pieces and one number line.
Definition The three energy steps
Δ H sub sublimation ): energy to turn solid metal into free gas atoms, M ( s ) → M ( g ) I.E. Δ H hyd hydration enthalpy ): energy released when water molecules cluster around the bare ion, M + ( g ) → M + ( a q ) 6.1.05-Hydration-enthalpy .
The Δ delta ) just means "change in", and H Δ H overall = Δ H sub + I.E. + Δ H hyd .
Li has the biggest I.E. but its tiny ion has a giant (very negative) Δ H hyd
Definition Standard reduction potentialE ∘ == E ∘ == gains electrons. A more negative E ∘ lose electrons (be a strong reducing agent). Li has E ∘ = − 3.04 V 5.3.02-Standard-reduction-potentials .
The figure lines up E ∘ left (more negative), the stronger the reducing power — and Li sits furthest left even though its bare-atom I.E. is the highest.
The flame-test section uses one energy-of-light equation. Here is every letter.
Δ E Δ E
ν nu ) = frequency of the light (how fast it wiggles).λ lambda ) = wavelength (distance between wave crests — this sets the colour ).h c Δ E = h ν = λ h c . Δ E λ
Atom: nucleus + shells + electrons
Flame colour dE = hc over lambda
Alkali metal trends and reactions
Cover the right side; can you answer each?
What the superscript ¹ in n s 1 The number of electrons in that s-orbital — exactly one loose valence electron.
What [ He ] A full, stable helium electron core, used as shorthand for the inner electrons.
The formula linking Z eff Z σ Z eff = Z − σ
Why going down the group weakens the grip on the outer electron A new shell is added so r σ Z
What the states ( g ) ( s ) ( a q ) Gas (free atoms), solid, and dissolved-in-water respectively.
What I.E. measures Energy to remove the outer electron from a free gaseous atom, M ( g ) → M + ( g ) + e −
Meaning of z + z − U ∝ z + z − / ( r + + r − ) The sizes of the positive and negative ion charges.
Why lattice energy U Big charges (top) and small radii (small denominator) both make U
The three terms in the aqueous energy cycle Sublimation Δ H sub Δ H hyd
Why Li is the strongest reducing agent despite highest I.E. Its tiny ion has a huge negative hydration enthalpy that overcompensates for the high I.E.
What a more negative E ∘ The metal more readily loses electrons — a stronger reducing agent.
What sets the flame colour in Δ E = h c / λ The wavelength λ Δ E
