Chemistry – Formulae & Equations (Chapter 6)

Question-and-answer flashcards covering naming of ionic and covalent compounds, valency, writing formulas, polyatomic ions, state symbols, solubility rules, balancing chemical equations, and ionic equations.

How is the name of an ionic compound constructed?

Name of the positive ion (cation) first, followed by the name of the negative ion (anion).

What change is made to a non-metal’s name when it forms a mono-atomic anion?

Its name ends with “-ide” (e.g. chlorine → chloride).

What is the anion name of fluorine?

Fluoride

What is the anion name of sulfur?

Sulfide

Product formed when calcium reacts with oxygen

Calcium oxide (CaO)

Two factors that determine the name of a covalent compound

1) Types of elements present; 2) Number of atoms of each element present

Suffix for covalent compounds that contain oxygen

-oxide (e.g. carbon dioxide)

Suffix for covalent compounds that contain chlorine

-chloride (e.g. silicon tetrachloride)

Prefix for 1 atom in covalent nomenclature

mono-

Prefix for 2 atoms in covalent nomenclature

di-

Prefix for 3 atoms in covalent nomenclature

tri-

Prefix for 4 atoms in covalent nomenclature

tetra-

Prefix for 5 atoms in covalent nomenclature

penta-

Prefix for 6 atoms in covalent nomenclature

hexa-

When may the prefix “mono-” be omitted?

When the first-named element has only one atom in the molecule.

Which element is named first in a covalent compound?

The element with the smaller Group number; the second element ends with “-ide.”

Name of SiF4

Silicon tetrafluoride

Name of CS2

Carbon disulfide

Define valency

Number of electrons lost, gained or shared during bonding; numerically equal to the ion’s charge.

Relationship between valency and charge

Valency equals the magnitude of the ionic charge (e.g. 2+ charge → valency 2).

Typical valency / charge of Group 17 elements

Valency 1, charge –1

Typical valency / charge of Group 16 elements

Valency 2, charge –2

Fixed ionic charges that must be memorised

Silver: +1; Zinc: +2

How are variable valencies shown in names?

Roman numerals in brackets after the metal name, e.g. iron(III) oxide.

Oxidation state of iron in FeCl₂

+2 (iron(II))

Five-step method to write an ionic formula

1) Write element symbols; 2) Write valencies/charges; 3) Reduce to lowest terms; 4) Cross valencies; 5) Write formula with subscripts.

Why are subscripts (not superscripts) used in formulas?

Subscripts show the number of atoms; superscripts would indicate charges.

Formula and charge of hydroxide ion

OH⁻, valency 1

Formula and charge of nitrate ion

NO₃⁻, valency 1

Formula and charge of carbonate ion

CO₃²⁻, valency 2

Formula and charge of sulfate ion

SO₄²⁻, valency 2

Formula and charge of phosphate ion

PO₄³⁻, valency 3

Formula and charge of ammonium ion

NH₄⁺, valency 1

Formula and charge of hydrogen carbonate ion

HCO₃⁻, valency 1

Formula and charge of dichromate(VI) ion

Cr₂O₇²⁻, valency 2

Rule for brackets with polyatomic ions in formulas

Enclose the ion in brackets before crossing valencies; remove brackets only if no subscript follows.

Meaning of state symbol (s)

Solid

Meaning of state symbol (l)

Liquid

Meaning of state symbol (g)

Gas

Meaning of state symbol (aq)

Aqueous – substance dissolved in water.

What does SPA stand for in solubility rules?

Salts of Sodium, Potassium and Ammonium – all are soluble.

Solubility of nitrates

All nitrates are soluble.

Insoluble exceptions for chloride/halide salts

Lead(II) halides and silver halides are insoluble.

Insoluble exceptions for sulfate salts

Calcium, lead(II) and barium sulfates are insoluble.

General solubility of carbonates

Most carbonates are insoluble except those of SPA metals.

Key information given by a chemical equation

Reactants & products, their amounts (mole ratios), and their physical states.

Definitions of reactants and products

Reactants: substances on the left of the arrow; Products: substances on the right of the arrow.

Four basic steps to balance a chemical equation

1) Write correct formulas; 2) Adjust coefficients to balance atoms; 3) Do not change subscripts; 4) Add state symbols if required.

Balancing tip for polyatomic ions

If a polyatomic ion appears unchanged on both sides, balance it as a single unit.

Which elements are usually balanced last?

Oxygen and hydrogen (start with the one present in the fewer number of molecules).

Definition of a spectator ion

An ion present in solution that does not undergo change during the reaction.

Four steps for writing an ionic equation

1) Write balanced equation with states; 2) Split aqueous substances into ions; 3) Cancel spectator ions; 4) Write remaining species.

Ionic equation for neutralisation of NaOH and HCl

OH⁻(aq) + H⁺(aq) → H₂O(l)