2. Seventh Grade Science

3. Isotopes (Copy into notes) Isotopes are atoms that have the same number of protons as the original atom, but more or less neutrons than the stable form of the atom The “average” atomic weight is shown on the Periodic Table of Elements because many of the elements have isotopes, different forms of the atom with more or less neutrons Shown below are isotopes of the element Carbon

4. Calculating Neutrons To calculate the number of neutrons in an atom, you subtract the atomic number (which is the number of protons) from the atomic mass (copy into notes) Ex. Carbon 14 Atomic mass: 14 Atomic number: - 6 Number of neutrons: 8 Therefore, Carbon 14 has 8 neutrons and is an isotope of carbon in its stable form!

5. Ions (copy all bullets into notes) Ions are atoms with extra electrons or missing electrons. When you are missing an electron or two, you have a positive charge. If an atom losses electrons, it forms a positive ion. When you have an extra electron or two, you have a negative charge. If an atom gains electrons, it forms a negative ion. Shown below is the Sodium ion

6. Representing Positive Ions When an element loses electrons and becomes a positively charged ion, it is depicted with a “+” charge to denote the loss of electrons (copy into notes) If the element loses 2 electrons, the charge would be noted with the element’s symbol with a +2 denoted similar to an exponent would be in math (copy into notes) Ex. Calcium forms positive ions when it loses 2 electrons and would be represented as Ca +2

7. Representing Negative Ions If the element gains electrons and becomes negatively charged, it is depicted with a “-” charge to denote the gain of electrons (copy into notes) Ex. Sulfur forms negative ions when it gains 2 electrons and would be represented as S -2

8. Quiz Time! Why do elements have “average” atomic weights listed on the Periodic Table of Elements? How are ions formed? Answer questions in notes!