Common elements and their symbols (first 30): Worked examples

Before we start, remember the four quantities the whole topic rests on (all built in the parent note):

Recall The four quantities (click to refresh)

Symbol ::: the 1- or 2-letter badge for an element (first letter CAPITAL, second lowercase).
Atomic number $Z$ ::: number of protons; it defines the element and its place in the table.
Mass number $A$ ::: total nucleons = protons + neutrons.
Neutron count ::: $A - Z$ (subtract protons from all nucleons).

See the map of how these connect: Atomic Number and Mass Number, Structure of the Atom.

The scenario matrix

Every question this topic can ask falls into one of these case classes. Each row is a distinct "shape" of problem; the worked examples below are tagged with which cell they hit.

Cell	Case class	What makes it tricky	Covered by
A	Symbol → element + $Z$ (normal)	none — the base skill	Ex 1
B	Symbol → element (Latin oddball)	badge ≠ English name	Ex 2
C	Capitalisation trap (Co vs CO)	1 element vs 2 atoms	Ex 3
D	Look-alike discriminator (N/Na, K/Kr)	shared first letter	Ex 4
E	Full notation $_{Z}^{A} X$ → neutrons	must subtract correctly	Ex 5
F	Degenerate / zero-neutron case	$A = Z$ (no neutrons)	Ex 6
G	Real-world word problem	translate words → symbols	Ex 7
H	Exam twist (reverse: neutrons → symbol)	work backwards	Ex 8
I	Limiting edge (heaviest of the first 30, $Z = 30$ )	end-of-range recall	Ex 9

The figure below is the "reference chart" we'll point back to for the first 30.

Figure — Common elements and their symbols (first 30)

Worked examples

Example 1 — Cell A: normal symbol lookup

Example 2 — Cell B: Latin oddball

Worked example Statement

Give the English name and $Z$ for the symbols K and Fe.

Forecast: neither badge looks like its English name. Which two famous "ancient" metals are these?

Spot that these are oddballs. "K" is not the first letter of any English element name; "Fe" isn't either. Why this step? When a badge doesn't match English, suspect an old Latin root (parent's "source 2").
Recall the Latin four. $K =$ Kalium → Potassium; $F e =$ Ferrum → Iron. Why this step? These four (Na, K, Fe, Cu) must be memorised separately — see the Hinglish note for the same list.
Read off $Z$ . Potassium is row 19 → $Z = 19$ . Iron is row 26 → $Z = 26$ . Why this step? Position in the ordered table gives $Z$ directly.

Answer: K = Potassium, $Z = 19$ ; Fe = Iron, $Z = 26$ .

Verify: Mnemonic "Naughty Kids Feel Curious" lists exactly these Latin four. ✓

Example 3 — Cell C: capitalisation trap

Worked example Statement

A student writes "CO" meaning cobalt. Is this correct? If not, fix it and say what "CO" actually means.

Forecast: does capitalising both letters change the meaning? Guess yes/no first.

Decode "CO" letter by letter. Two capital letters = two separate symbols: C then O. Why this step? The rule "second letter is lowercase" means every new capital starts a new element.
Translate each capital. C = carbon, O = oxygen. So "CO" = a compound: carbon monoxide. Why this step? Capitalisation encodes how many atoms/elements are being described — it's information, not decoration.
Write cobalt correctly. Cobalt = one element = Co (capital C, lowercase o). Why this step? One element ⇒ one capital + one lowercase.

Answer: "CO" is wrong for cobalt. Cobalt = Co. "CO" = carbon monoxide (two elements).

Verify: Cobalt is row 27 ( $Z = 27$ ) in the table, listed as Co, confirming the lowercase o. ✓

Example 4 — Cell D: look-alike discriminator

Worked example Statement

Distinguish the four badges N, Na, K, Kr. Name each and give $Z$ for the three within the first 30.

Forecast: N and Na share a first letter; K and Kr share a first letter. What single feature tells them apart?

Use letter-count as the discriminator. N (one letter) vs Na (two letters); K (one letter) vs Kr (two letters). Why this step? The parent's fix: "one letter vs two letters is the discriminator."
Assign names. N = Nitrogen; Na = Sodium; K = Potassium; Kr = Krypton. Why this step? Matching each badge to its correct element removes the confusion.
Read off $Z$ (within first 30). N = 7, Na = 11, K = 19. Kr has $Z = 36$ , beyond our range. Why this step? We only memorised 1–30; flagging Kr as out-of-range is part of "covering the edge."

Answer: N = Nitrogen ( $Z = 7$ ), Na = Sodium ( $Z = 11$ ), K = Potassium ( $Z = 19$ ), Kr = Krypton ( $Z = 36$ , outside first 30).

Verify: Rows 7, 11, 19 in the table read N, Na, K exactly. ✓

Example 5 — Cell E: full notation → neutrons

Example 6 — Cell F: degenerate zero-neutron case

Example 7 — Cell G: real-world word problem

Worked example Statement

A water molecule is described as "two hydrogen atoms bonded to one oxygen atom." Write its chemical formula using symbols, then state the atomic numbers of the elements involved.

Forecast: which letters, and where do the "counts" go? Guess the formula.

Translate each name to a symbol. Hydrogen → H, Oxygen → O. Why this step? Symbols are the universal shorthand (parent's whole point of "H₂O is universal").
Attach counts as subscripts. Two hydrogens → $H_{2}$ ; one oxygen → $O$ (a "1" is left unwritten). Why this step? Subscripts encode how many atoms of each element — the count lives to the lower-right.
Assemble and read $Z$ . Formula: $H_{2} O$ . Hydrogen $Z = 1$ , Oxygen $Z = 8$ . Why this step? Reading off $Z$ links the word problem back to periodic-table position.

Answer: $H_{2} O$ ; Hydrogen $Z = 1$ , Oxygen $Z = 8$ .

Verify: Rows 1 and 8 of the table are H and O. ✓ The subscript 2 sits after H, not capitalised, so no "H2O vs HO2" confusion.

Example 8 — Cell H: exam twist (work backwards)

Worked example Statement

An element within the first 30 has 13 protons. In an atom of it with 14 neutrons, what is the mass number $A$ , and what is the full notation $_{Z}^{A} X$ ?

Forecast: you're given protons and neutrons — which quantity do you build first? Guess before reading.

Get $Z$ and identify the element. protons $= Z = 13$ ⇒ row 13 ⇒ Aluminium, symbol Al. Why this step? $Z$ = protons, and $Z$ pins down the element name and badge.
Rebuild $A$ from its parts. $A = protons + neutrons = 13 + 14 = 27$ . Why this step? Here we run the neutron formula in reverse — adding, because $A$ is the total.
Assemble the notation. Superscript $A = 27$ , subscript $Z = 13$ , symbol Al ⇒ $_{13}^{27} Al$ . Why this step? Placing $A$ and $Z$ in their fixed slots produces the standard written form.

Answer: $A = 27$ ; full notation $_{13}^{27} Al$ .

Verify: neutrons $= A - Z = 27 - 13 = 14$ ✓ — matches the given neutron count. ✓

Example 9 — Cell I: limiting edge (top of the range)

Worked example Statement

Name the element at the very end of our first-30 list ( $Z = 30$ ), give its symbol, and state its position among the transition metals iron→zinc.

Forecast: the last row — a two-letter symbol starting with Z. Which element?

Read the last row. $Z = 30$ is row 30 — the final entry we memorise. Why this step? The "limiting value" of the range is a common recall target.
Name and symbol. $Z = 30$ ⇒ Zinc, symbol Zn (capital Z, lowercase n). Why this step? Confirms the two-letter capitalisation rule at the boundary.
Place it in the Fe→Zn run. The order 26–30 is Fe, Co, Ni, Cu, Zn ⇒ Zinc is the 5th and last. Why this step? Anchoring Zn as the end of the transition-metal stretch aids ordered recall — see Metals Nonmetals and Metalloids.

Answer: Zinc, Zn; it is the 5th (last) in Fe, Co, Ni, Cu, Zn.

Verify: Counting 26→30 gives exactly 5 elements: Fe(26), Co(27), Ni(28), Cu(29), Zn(30). ✓

Connections

Parent: first 30 symbols — the rules these examples exercise.
Atomic Number and Mass Number — the $Z$ and $A$ used throughout.
Structure of the Atom — protons/neutrons behind every count.
Isotopes — why $_{1}^{1} H$ (Ex 6) is one of several hydrogens.
Metals Nonmetals and Metalloids — the Fe→Zn run in Ex 9.
Valency and Electron Configuration — the next step once symbols are fluent.

Recall Rapid self-test

Neutrons in $_{13}^{27} Al$ ? ::: $27 - 13 = 14$ . Symbol + $Z$ of the element at the end of the first 30? ::: Zn, $Z = 30$ . What does "CO" mean, and how do you write cobalt? ::: CO = carbon + oxygen; cobalt = Co.