HESI A2 Chemistry

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Sample questions from HESI A2 Chemistry

This material has 30 questions with answers and rationales. Here are the first 5.

1. 1.**An atom has 11 protons and 12 neutrons. What is its mass number?**

   • A.12.
   • B.24.
   • C.23.
   • D.11.

   Rationale: Mass number is the total number of protons and neutrons, so 11 + 12 = 23. Eleven is the proton count, and 12 is the neutron count; neither alone is the mass number. Twenty-four is one more than the correct total.

2. 2.**Which particle determines the identity of an element?**

   • A.Electron.
   • B.Proton.
   • C.Isotope.
   • D.Neutron.

   Rationale: An element is defined by its number of protons, called its atomic number. Neutrons can vary among isotopes, and electrons can vary when ions form, without changing the element's identity. An isotope is a form of an element, not a subatomic particle.

3. 3.**How many electrons does a neutral atom with atomic number 8 have?**

   • A.10.
   • B.6.
   • C.16.
   • D.8.

   Rationale: A neutral atom has equal numbers of protons and electrons, and atomic number 8 means it has 8 protons. Six and 10 would not balance the positive charge of its protons. Sixteen is not the electron count; it may be confused with a mass number for a common oxygen isotope.

4. 4.**Which formula represents a molecule containing two hydrogen atoms and one oxygen atom?**

   • A.H2O.
   • B.H2O2.
   • C.2HO.
   • D.HO2.

   Answer and rationale are in the full material.

5. 5.**Which type of bond forms when atoms share electrons?**

   • A.Ionic bond.
   • B.Hydrogen bond.
   • C.Metallic bond.
   • D.Covalent bond.

   Answer and rationale are in the full material.