According to this scale fluorine is the most electronegative element with a value of 40 and cesium is the least electronegative element. The number of particles atoms molecules or ions present in 1 mole of any substance is fixed with a value of 6022 x 10 23. Atoms And The Periodic Table Activities Game For Learning Atomic Structure Middle School Science Experiments Physical Science Activities Middle School Science Classroom Memorize flashcards and build a practice test to quiz yourself before your exam. . The most commonly encountered numbers are 4 and 6. IONS If an atom gains or loses one or more electrons it acquires a net electric charge and becomes an ion. Ions which are a part of the science subject Chemistry forms from atoms and electrons that have either gained or lost their weight by the removal or adding of one or more valence electrons which would create either positive or a negative charge. If two atoms differ c...