Elements, Compounds and MixturesCambridge IGCSE Chemistry: Flashcards

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What is an element?

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What is an element?: A substance made of only one type of atom.
What is a compound?: Two or more elements chemically combined together in fixed proportions, forming a new substance with different properties.
What is a mixture?: Two or more substances mixed together but not chemically combined; each keeps its own properties and can be separated by physical methods.
How can you separate a compound back into its elements?: Only by a chemical reaction — the chemical bonds must be broken.
Describe the basic structure of an atom.: A central nucleus containing protons and neutrons, surrounded by electrons arranged in shells.
What is the relative charge and relative mass of a proton?: Relative charge +1, relative mass 1.
What is the relative charge and relative mass of a neutron?: Relative charge 0, relative mass 1.
What is the relative charge and relative mass of an electron?: Relative charge -1, relative mass very small (often taken as 0).
Why is an atom overall neutral?: Because the number of protons (positive) equals the number of electrons (negative).
What is proton (atomic) number?: The number of protons in the nucleus of an atom; it defines which element the atom is.
What is mass (nucleon) number?: The total number of protons and neutrons in the nucleus of an atom.
How do you calculate the number of neutrons in an atom?: Neutrons = mass number − proton number.
An atom has proton number 11 and mass number 23. How many neutrons does it have?: 12 neutrons (23 − 11 = 12).
What is the maximum number of electrons in the first three electron shells?: 2, then 8, then 8.
What is the electronic configuration of an atom with 13 electrons?: 2,8,3.