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Chemistry: The Periodic Table
Question
What is the periodic table?
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Answer
A table of all known chemical elements arranged in order of increasing atomic number, grouped by similar properties.
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Question
What is atomic number?
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Answer
The number of protons in the nucleus of an atom. It uniquely identifies each element.
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Question
What is mass number?
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Answer
The total number of protons and neutrons in an atom's nucleus.
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Question
What are periods in the periodic table?
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Answer
Horizontal rows. The period number indicates the number of electron shells an atom has.
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Question
What are groups in the periodic table?
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Answer
Vertical columns. Elements in the same group have the same number of outer electrons and similar chemical properties.
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Question
What are the alkali metals (Group 1)?
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Answer
Li, Na, K, Rb, Cs, Fr — highly reactive metals that form +1 ions and react vigorously with water to produce hydrogen gas and a metal hydroxide.
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Question
What are the halogens (Group 17)?
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Answer
F, Cl, Br, I, At — reactive non-metals that form −1 ions. Reactivity decreases down the group.
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Question
What are the noble gases (Group 18)?
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Answer
He, Ne, Ar, Kr, Xe, Rn — chemically inert gases with full outer electron shells.
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Question
What is electronegativity and how does it trend across the table?
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Answer
The tendency of an atom to attract electrons in a bond. It increases across a period (left to right) and decreases down a group.
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Question
What is ionisation energy and how does it trend?
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Answer
The energy needed to remove an electron from a gaseous atom. It increases across a period and decreases down a group.
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