How protons, neutrons, and electrons build an atom, and how the periodic table's rows and columns predict an element's behaviour, a recurring pattern on the HESI A2 chemistry subtest.
ObjectiveC.1.3Read6 minExam weightMatter and Measurement ≈ 28% of Chemistry
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You can name the three subatomic particles, their charges, and where each sits in an atom.
You can use an element's atomic number and mass number to find its protons, neutrons, and electrons.
You can read a periodic table group and period to predict an element's reactivity and electron arrangement.
What the lesson concludes
The atomic number is the proton count and it defines the element. Change it and you have a different element.
Mass number is protons plus neutrons. Subtract atomic number from mass number to find neutrons.
Isotopes of the same element share a proton count but differ in neutron count, which is why atomic weight on the table is an average, not a whole number.
Elements in the same group share the same number of valence electrons, which is why they react in similar ways.
Electrons fill shells in a set order, and the outermost shell's occupancy is what makes an atom stable or reactive.