20 Questions
What is the chemical formula for carbon tetrachloride?
CCl4
According to the rules for writing a chemical formula, which element is written first in a compound of a metal and a non-metal?
Metal
When a compound consists of polyatomic ions, how is the number of ions present in the compound indicated?
By placing the number of ions outside the brackets enclosing the formula of the polyatomic ion
What is the chemical formula for aluminium oxide?
Al2O3
In magnesium chloride, how many chloride ions are present for each magnesium ion?
Two chloride ions for each magnesium ion
What is the combining power of an element known as?
Valency
How can the valency of an element be represented according to the text?
As hands or arms of an octopus
What does the subscript 4 in OH4 represent?
The number of humans held by the octopus
Which term is used to describe a group of atoms carrying a charge?
Polyatomic ion
In Table 3.5, what does the Roman numeral in brackets represent for certain elements?
Valency
What is the combining power (or capacity) of an element known as?
Valency
How can the valency of an element be thought of according to the text?
As the number of arms or hands an atom has
What does a Roman numeral in brackets represent for certain elements?
Valency of the element
How is the number of ions present in a compound indicated when it consists of polyatomic ions?
Through a subscript
Which term describes a group of atoms carrying a charge?
Polyatomic ion
What is the correct chemical formula for calcium oxide?
CaO
In the formula for magnesium chloride (MgCl2), why are there two chloride ions for each magnesium ion?
The charges on the ions need to balance
Why is the chemical formula for aluminium oxide simplified to Al2O3 instead of Al2O2?
To balance the charges on the ions
What rule must be followed when writing a chemical formula for a compound consisting of a metal and a non-metal?
The name or symbol of the metal is written first
What is the purpose of using brackets when writing a chemical formula for compounds formed with polyatomic ions?
To indicate the number of polyatomic ions present in the compound
Study Notes
Chemical Formulae Rules
- The chemical formula for carbon tetrachloride is CCl4.
- In a compound of a metal and a non-metal, the metal is written first.
Polyatomic Ions
- When a compound consists of polyatomic ions, the number of ions present is indicated by a subscript outside the brackets.
Valency and Combining Power
- The combining power of an element is known as its valency.
- The valency of an element can be represented by a Roman numeral in brackets or thought of as the number of electrons an element gains or loses to form a stable ion.
Formulae for Compounds
- The chemical formula for aluminium oxide is Al2O3.
- The chemical formula for calcium oxide is CaO.
- The chemical formula for magnesium chloride is MgCl2, with two chloride ions for each magnesium ion.
Writing Chemical Formulae
- When writing a chemical formula for a compound consisting of a metal and a non-metal, the metal must be written first.
- When writing a chemical formula for compounds formed with polyatomic ions, brackets are used to indicate the polyatomic ion, and a subscript outside the brackets indicates the number of ions present.
This quiz covers the formation of ions, symbols and combining capacity of elements, and the concept of valency in chemistry. It explores how the valency of an element determines its ability to combine with atoms of other elements to form chemical compounds.
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