A binary ionic compound is composed of mono-atomic metal cations and mono-atomic non-metal anions. To write the name of an ionic compound, the cation is named first followed by the name of anion. How do you name cations and anions? The name of the cation is the same as the name of the metal, but in the name of mono-atomic anion, the suffix ide is added to the root name of the element. For example, sodium chloride, magnesium oxide, aluminium nitride, etc.
The following steps are used to write the chemical formula of a binary ionic compound.
For example, the chemical formula of sodium chloride is written as follows;
Na Cl +1 -1 → NaCl
Example 2, the chemical formula of aluminium oxide is written as follows;
Al O +3 -2 → Al2O3
| Cations | Anions |
|---|---|
| Lithium | Fluoride |
| Sodium | Chloride |
| Potassium | Bromide |
| Magnesium | Nitrite |
| Calcium | Nitrate |
| Copper | Sulfate |
How do you count your shoes? Since the shoes come in pairs, you'll probably count them in pairs rather than individually. Likewise, eggs, oranges, etc. are counted in the dozens, but paper with the ream. So the unit of counting depends on what you are counting. Chemists also use a practical unit for counting atoms, molecules and ions. They use a counting unit called mole to measure the amount of a substance.
A mole is an amount of a substance that contains 6.022 x 1023 particles of that substance. This experimentally determined number is known as Avogadro's number. It is represented by NA. Just as a dozen eggs represent twelve eggs, a ream of paper represent 500 papers, a mole of a substance represents 6.022 x 1023 representative particles of a substance. For example a mole of carbon is 6.022 x 1023 atoms. A mole of sulfur is 6.022 x 1023 atoms. A mole of water is 6.022 x 1023 molecules.
What is the mass of one mole C-atoms?
How many atoms are there in 32.1 g of S-atoms?
Does a dozen eggs have the same mass as a dozen bananas? Does a mole of carbon atoms have a different mass than a mole of sulfur atoms?
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Size of the Mole
Entire population cannot count 1 mole of coins in a year. They need about one million years to count them. So, when counting a pile of coins, it would not be convenient to count them one by one. The concept of mole has given a very simple method to count large number of items. Mole is not only a number but also represents a definite amount of a substance. Just as 6.022 x 1023 carbon atoms weigh 12 g, 6.022 x 1023 coins will also have a definite mass. So an easy way is to weigh them. If you know the mass of one coin, you can count them by weighing.
The mass of one mole of a substance is called molar mass. What are the molar masses of carbon and sulfur? The term representative particles in a substance are atoms, molecules, formula units or ions. For instance, water exists as molecules, hydrogen exists as H2 molecules, so one mole of hydrogen contains 6.022 x 1023 molecules, carbon exists as atoms so 1 mole of carbon contains 6.022 x 1023 atoms.
What is the mass of 6.022 x 1023 S-atoms?
What is the mass of one mole of C-atoms?
Is this mass of S-atoms equal to its atomic mass?
Is this mass of C-atoms equal to its atomic mass?
Atomic mass of an element expressed in grams is called gram atomic mass. Is the gram atomic mass of C-atoms 12 g? What is the gram atomic mass of S-atoms?
If each of the carbon and sulfur sample shown above contains one mole of atoms, why do the samples have different masses?
Atomic mass of C = 12 amu
Gram atomic mass of C = 12 g
Atomic mass of Na = 23 amu
Gram atomic mass of Na = 23 g
Atomic mass of Zn = 63.54 amu
Gram atomic mass of Zn = 63.54 g
Gram atomic mass of an element contains 1 mole of atoms. Therefore,
Mass of 1 mole of C-atoms = 12 g
Mass of 1 mole of Na-atoms = 23 g
Mass of 1 mole of Zn-atoms = 63.54 g
A mole of H2O-molecules (6.022 x 1023 H2O-molecules) = 18.016 g
A mole of CaH2O-molecules (6.022 x 1023 CHO-molecules) = 180.096 g
What is the mass of one mole of water molecules? Is this mass of water molecules equal to the molecular mass of water?
What is the mass of 6.022 x 1023 molecules of glucose? Is this mass of glucose molecules equal to the molecular mass of glucose?
Molecular mass of a substance expressed in grams is called gram molecular mass.
Molecular mass of H2O = 2 x 1.008 + 16 = 18.016 amu = 18.016 g
Molecular mass of C6H12O6 = 6 x 12 + 12 x 1.008 + 16 x 6 = 180.096 amu = 180.096 g
Therefore, gram molecular mass of C6H12O6 = 180.096 g
Formula mass of a substance expressed in grams is called gram formula mass.
An ionic compound is represented by the formula unit that represents the simplest ratio between the ions of a compound. For example NaCl, KCl, CuSO4, etc.
Formula mass of NaCl = 23 + 35.5 = 58.5 amu = 58.5 g
Formula mass of KCl = 39 + 35.5 = 74.5 amu = 74.5 g
1. Gram atomic mass represents one mole of atoms of an element, gram molecular mass represents one mole of molecules of a compound or an element that exists in molecular state whereas gram formula mass represents one mole of ionic formula units of a compound.
2. Gram atomic mass contains 6.022 x 1023 atoms, gram molecular mass contains 6.022 x 1023 molecules whereas gram formula mass contains 6.022 x 1023 formula units.
3. All of these quantities represent molar mass. Mass of one mole of a substance expressed in grams is called molar mass. Therefore, mole can be defined as atomic mass, molecular mass or formula mass expressed in grams.