June 2017 NY Regents Chemistry Exam
3 What is the number of electrons in an atom of scandium? (1) 21
(2) 24 (3) 45
(4) 66
Solution: In a neutral atom, the number of protons is equal to the number of electrons. All we need to do is to find the number of protons for scandium. Atomic number equals the number of protons. We can find atomic number on the Periodic Table at the bottom of the element. It is 21 for scandium. This means there are 21 protons and 21 electrons in an atom of scandium.
Ps: Not sure what the symbol for scandium is? Table S on the Reference Table has the names of the elements as well as abbreviations.
Answer: 1
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