10.3Chapter 10: Structure, Bonding, and Properties

Making ions — Alhussan Chemistry - Stage 9 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 9 2 quizzes

📚 Alhussan Chemistry - Stage 9 Hub / Topical Revision

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10.3 Making ions — Cations, Anions and Full Outer Shells — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define ion, describe how ions form, explain why atoms form ions and write formulae for simple ions.Ion = a particle with a positive or negative charge, formed…

Negative ion
Positive ion
Importance
Sodium ion
Chloride ion
Stable atoms

Part 1 of 7What ions are

Ion

Ion a particle with a positive or negative charge, formed when an atom gains or loses electrons.

Negative ion

Negative ion an atom that gains one or more electrons becomes negatively charged, because electrons are negative.

Positive ion

Positive ion an atom that loses one or more electrons becomes positively charged.

Protons

Protons the number of protons does not change, only the number of electrons.

Importance

Importance animals such as goats need sodium ions from salt to make their hearts and nerves work.

Part 2 of 7How sodium chloride ions form

Before

Before a sodium atom has 11 protons and 11 electrons, and a chlorine atom has 17 protons and 17 electrons, so neither has a net charge.

Transfer

Transfer in the reaction one electron moves from the sodium atom to the chlorine atom.

Sodium ion

Sodium ion it has 11 protons and 10 electrons, so its charge is +1.

Chloride ion

Chloride ion it has 17 protons and 18 electrons, so its charge is -1.

Part 3 of 7Cations and anions

Cations

Cations metals lose outer electrons to form positive ions called cations.
Sodium (2,8,1) loses one electron to become Na⁺ (2,8), and magnesium (2,8,2) loses two to become Mg²⁺.

Anions

Anions non-metals gain electrons to form negative ions called anions.
Chlorine (2,8,7) gains one to become Cl^- (2,8,8), and oxygen (2,6) gains two to become O^2-.

Group	Change	Charge	Example
1	Lose 1	+1	Li⁺
2	Lose 2	2+	Ca²⁺
3	Lose 3	3+	Al³⁺
6	Gain 2	2-	S^2-
7	Gain 1	1-	F^-

Part 4 of 7Why atoms form ions

Stable atoms

Stable atoms argon makes up 1% of the air and is inert because its atoms have eight electrons in a full outer shell.

Full outer shell

Full outer shell any atom or ion with a full outer shell is stable.

Purpose

Purpose ions form to achieve a stable noble gas electron arrangement.
Na⁺, Mg²⁺, F^- and O^2- have the neon arrangement 2,8.
K⁺, Ca²⁺, Cl^- and S^2- have the argon arrangement 2,8,8.

Sodium chloride

Sodium chloride it is made of stable ions, each with a full outer shell, which explains why it takes part in few chemical reactions.

Part 5 of 7Formulae for ions

Formulae for ions

Format

Format the formula gives the chemical symbol of the element and the charge on the ion.
The + or - sign is written to the right of the symbol and above the line.

Examples

Examples a sodium ion is Na⁺, a chloride ion is Cl^-, a potassium ion is K⁺, a magnesium ion is Mg²⁺ and a bromide ion is Br^-.

Charge style

Charge style write the number first then the sign, as in 2-.

Counting particles

Counting particles for Mg²⁺ the electrons are 12 - 2 = 10, and for O^2- (atomic number 8) they are 8 + 2 = 10.
- (atomic number 12)

Part 6 of 7Size of atoms and ions

Positive ions

Positive ions a sodium ion is smaller than a sodium atom because the whole outer shell is lost.

Negative ions

Negative ions a chloride ion is bigger than a chlorine atom because the extra electron increases repulsion in the outer shell.

Part 7 of 7Ionic formulae

Balanced charges

Balanced charges the total positive charge must equal the total negative charge, and the charges are not written in the formula.

Crossover method

Crossover method the number of each ion's charge becomes the subscript of the other ion.

Examples

Examples aluminium oxide is Al₂O₃, calcium fluoride is CaF₂, potassium sulfide is K₂S and sodium oxide is Na₂O.

Key terms

Term	Meaning
Ion	a charged atom or group of atoms.
Cation	a positively charged ion.
Anion	a negatively charged ion.
Full outer shell	a stable electron arrangement like a noble gas.
Inert	not taking part in chemical reactions.
Chloride ion	the Cl^- ion formed when chlorine gains an electron.