Class 9

9.4.4 Chemical Formula of Binary Ionic Compounds

This is the fourth lecture from Chapter 4: “Stoichiometry” in the new Class 9 Chemistry book (Punjab Board – PCTB). It discusses the steps to write the chemical formula of binary ionic compounds. The lecture also includes a multiple-choice quiz, short question and long question notes.

MCQs Based Quiz

9.4.4 Chemical Formula of Binary Compounds

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Hydrogen (H) can form ions with which charge

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Which charge does lithium (Li) always exhibit when ionized?

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The alkaline earth metal magnesium (Mg) forms ions with:

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The typical ionic form of chlorine (Cl) is:

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Which halogen forms a 1- ion?

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Copper (Cu) is an unusual element because it can form:

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What is the charge on ions formed by Iron (Fe):

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Ions of tin (Sn) can have the following charge(s):

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Aluminium (Al) ionizes to form:

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Nickel (Ni) forms ions with:

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Which pair shows elements with only one possible ionic charge?

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Among these, which element has the highest positive charge when ionized?

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What ion does sodium (Na) always form?

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Lithium (Li) typically becomes which ion?

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Potassium (K) in ionic form is:

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Calcium (Ca) always forms:

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Barium (Ba) in compounds appears as:

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Zinc (Zn) always forms:

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Oxygen forms which anion?

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The ionic form of nitrogen is:

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Iodine (I) becomes:

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Which pair shares the same ionic charge?

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Among these, which element can have multiple charges?

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Short Questions

Q1. What are the basic steps to write the formula of an ionic binary compound?

  1. Identify the cations and anions and the number of charges present on them.
  2. Combined the two ions together to form an electrically neutral compound.

Q2. Write down the formula of lithium oxide.

The formula of lithium oxide is Li2O.

Q3. Write down the formula of aluminium oxide.

The formula of aluminium oxide is Al2O3.

Q4. An ionic compound is made up of two ions: Ba2+ and N3-. Write its chemical formula.

Chemical Formula of Ba3N2

Q5. An ionic compound is made up of lithium and oxygen ions. Write its chemical formula.

Chemical Formula of Li2O

Q6. Write the chemical formula of an ionic compound that is made up of aluminium and oxygen ions.

Chemical Formula of Al2O3

Q7. What would be the chemical formula of an ionic compound that is made up of magnesium and nitrogen ions?

Chemical Formula of Mg3N2

Q8. Write the chemical formula of the ionic compounds that are made up of following pair of ions:

(a) Al3+ & I1-

Chemical Formula of AlI3

(b) Fe3+ & N3-

Chemical Formula of FeN

(c) Mg2+ & O2-

Chemical Formula of MgO

(d) Sn4+ & N3-

Chemical Formula of Sn3N4

(e) Ni2+ & O2-

Chemical Formula of NiO

Atoms with Their Cations and Anions

Atoms

Cations / Anions

H

H1+

Na

Na1+

Li

Li1+

K

K1+

Mg

Mg2+

Ca

Ca2+

Ba

Ba2+

Zn

Zn3+

Al

Al3+

Cu

Cu1+, Cu2+

Fe

Fe2+, Fe3+

Sn

Sn2+, Sn4+

Ni

Ni2+

O

O2-

N

N3-

Cl

Cl1-

Br

Br1-

I

I1-

Descriptive Question

Q1. How will you write chemical formulas of binary ionic compounds?

Following are the steps to write the chemical formulas of binary ionic compounds.

  1. Identify the cations and anions and the number of charges present on them.
  2. If the number of charges on opposite ions are equal, then simply combine them to form an electrically neutral compound.
  3. If the charges are not equal, apply crisscross method to write the formula.
  4. Exchange the numerical value of charges (not the sign) and use them as subscripts for the opposite charge.
  5. Combine the ions and their subscripts.

Examples:

To write the chemical formula of lithium oxide, we follow these steps:

Chemical Formula of Li2O

To write the chemical formula of aluminium oxide, we also follow the same steps:

Chemical Formula of Al2O3

The chemical formula of magnesium nitride can be written as follows:

Chemical Formula of Mg3N2