Name: Bonding: Atoms and Molecules What do the rows represent? The rows in the periodic table correspond to the number of energy levels of the atoms in that row. So the atoms in the first row have one energy level, the atoms in the second row have two energy levels and so on. Understanding how electrons are arranged within the energy levels can help explain why the periodic table has as many rows and columns as it does. Let s take a closer look. Electrons and Energy Levels Every atom contains different energy levels that can hold a specific number of electrons. For a moment, let s imagine the simplest possible scenario: once all the positions are occupied within one energy level, any remaining electrons begin filling positions in the next energy level. To picture this, imagine people filling rows of chairs in an auditorium. If each person sits next to another person until one row is filled, any remaining people must begin taking their seats in the 2nd row, and so on. Not so bad, right? In general, this simple case is a helpful analogy. Electrons fill a given section until it is full, and then any more electrons move on to another unoccupied section where they continue filling there. Electrons begin filling the lowest energy level (closest to the nucleus) and then move on to higher energy levels (further form the nucleus). Energy levels Electrons surround the nucleus of an atom in regions called energy levels. Even though atoms are spherical, the energy levels in an atom are more easily shown in concentric circles. Which atom is this supposed to be? The larger dot in the center of this atom represents the nucleus, which contains both protons and neutrons. The smaller dots surrounding the nucleus represent electrons. In order to figure out which atom this represents, count up the number of electrons. There are 8 electrons in this atom. Because the number of electrons and protons is the same in an atom, this atom has 8 protons. Look at the chart Periodic Table, Elements 1 20. The number of protons is the same as the atomic number, so this drawing represents an oxygen atom.
Explain It: If you look closely at the tip of a sharpened pencil, you will see that it is made of graphite. Going deeper, graphite is made of carbon atoms. Deeper still, each carbon atom is made of protons, neutrons, and electrons. 1. Label the nucleus (protons, neutrons) and electrons in the drawing of a carbon atom to the right. 2. Draw a line between the subatomic particle and its charge. proton electron neutron no charge positive charge negative charge 3. Write a short caption under each picture to describe the process of covalent bonding. 4. What are two conditions atoms must have in order to form covalent bonds with one another? 5. Why is a hydrogen molecule (H 2 ) more stable than just two individual hydrogen atoms? 6. Why can t a third hydrogen atom join the H 2 molecule to make H 3?
7. Write a short caption beside each picture to describe the process of covalent bonding: 8. Why can t a third hydrogen atom join the water molecule H 2 O to make H 3 O? 9. What is the basic difference between covalent and ionic bonding?
10. Write a short caption beside each picture to describe the process of ionic bonding:
In the beginning of this packet, you saw energy level models for each atom that used concentric circles to represent energy levels and dots for electrons. These diagrams were also used to show what happens to the electrons when different atoms bond. Sometimes electrons were shared (covalent bonding) and sometimes electrons were transferred from one atom to another (ionic bonding). There is a common, shorthand way to represent bonding called Lewis dot diagrams. Dots still represent electrons, but they are drawn around the symbol for the element. And only the electrons in the outermost energy level are drawn. 11. Compare the periodic table of energy levels to the Lewis dot diagrams. Look at the dots around each symbol and the energy levels in your chart. What relationship do you notice between the dots in these two charts? 12. The number of dots near hydrogen and helium are the same as in the energy level chart. Why?