What is a chemical formula?
A representation of a substance using symbols for the elements it contains.
AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Foundation · 5.1.1.1
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What is a chemical formula?
A representation of a substance using symbols for the elements it contains.
What does a compound’s chemical formula show about its constituent atoms?
Which elements are present and the fixed proportions in which their atoms are chemically combined.
What are chemical formulae used for?
To identify substances and name them correctly.
What is the periodic table used for in this course?
To identify element names and symbols.
Which sets of elements should you be able to use the names and symbols for in this course?
What is the role of a chemical symbol in chemistry?
A chemical symbol is the standard shorthand used to represent an element.
What is a compound?
A substance made of atoms of two or more different elements chemically combined.
What does it mean that elements in a compound are joined in fixed proportions?
A given compound always has the same composition.
How does a compound differ from a physical mixture of its elements?
A compound is a new substance in which the elements are chemically combined.
How can a compound be represented?
By a chemical formula.
How can a compound be separated back into its elements?
Only by chemical reactions.
What are all substances made from?
Atoms.
About how many different elements are there?
About 100.
What are the basic building blocks from which other substances are made?
Elements.
What is an atom?
The smallest part of an element that can exist as that element.
What is an element?
A pure substance made from only one type of atom.
What makes a chemical equation balanced?
Each element has the same number of atoms on the reactant and product sides.
What do coefficients in a chemical equation indicate, and where are they written?
They indicate the number of whole particles and are written in normal script before a formula.
What do subscripts in a chemical formula indicate?
The number of atoms of each element in one particle of the substance.
When balancing a chemical equation, which numbers may be changed and which must remain unchanged?
Change the coefficients; leave the subscripts in the formulas unchanged.
What is a chemical reaction?
A transformation of starting substances called reactants into one or more new substances called products.
What happens to atoms and chemical bonds during a chemical reaction?
Atoms are rearranged as chemical bonds change.
What can form when elements react chemically?
Compounds.
In which directions can energy be transferred during a chemical reaction?
To or from the surroundings.
Is an energy change detectable in every chemical reaction?
No. Energy changes are often detectable, but not necessarily in every reaction.