Practice Atomic Number in Chemistry
Use these practice problems to test your method after reviewing the concept explanation and worked examples.
Quick Recap
The number of protons in an atom's nucleus, which uniquely identifies the element and determines its position in the periodic table.
The atom's ID number — always means carbon, no matter what else changes.
Showing a random 20 of 50 problems.
Example 1
challengeA nuclear reaction emits a beta particle (an electron from the nucleus, as a neutron becomes a proton). How do and change?
Example 2
easyCan two different elements share the same atomic number?
Example 3
mediumIf a nucleus gains a proton through a nuclear process, how does its atomic number change and what happens to its identity?
Example 4
easyHow many protons does a neutral atom with and 12 neutrons have?
Example 5
mediumAn ion is with 18 electrons. What is sulfur's atomic number?
Example 6
hardWhy can two isotopes of an element have the same atomic number but different atomic masses?
Example 7
mediumAn atom has and 20 neutrons. Find the mass number.
Example 8
hardMoseley's X-ray experiments showed that one nuclear quantity correlates with X-ray frequency. Which one?
Example 9
challengeMendeleev first ordered elements by atomic mass, but a few pairs were out of order. Why is ordering by atomic number better?
Example 10
mediumAn ion has and 18 electrons. State its charge and identify the species.
Example 11
mediumA neutral atom of element X has 18 electrons. Its atomic mass is . Which element is X?
Example 12
easyWhat element has atomic number 26?
Example 13
easyTrue or false: a neutral atom has the same number of electrons as its atomic number.
Example 14
mediumThe atomic mass of chlorine is listed as 35.5. Why is the atomic number 17, a whole number, instead?
Example 15
mediumElement A is directly to the right of element B on the periodic table. How do their atomic numbers compare?
Example 16
easyAn atom has atomic number 1. What element is it?
Example 17
mediumIf a nucleus emits an alpha particle (2 protons, 2 neutrons), how does change?
Example 18
easyCan the atomic number of an atom change during a chemical reaction?
Example 19
easyWhat does atomic number tell you about an element's place in the periodic table?
Example 20
mediumElements are placed in order of increasing atomic number. Which comes first in the table, or ?