1. The Chemistry of Living Things II Ionic and covalent bonding, ions and isotopes. Individual carbon atoms

2. Before we go on…. Yesterday I was asked if I knew all the elements by memory. I don’t but here is someone who does…enjoy. The elements of the periodic table

3. Ions So far we’ve learned about atoms. In each case our atoms had the same number of electrons (-) and protons (+). Because of this every atom as an overall net charge of zero. Eg. Carbon 6 (-) + 6(+) = 0.

4. Atoms and reactivity. Atoms are most stable when they have a full outermost level of electrons. This is called the octet rule. This outer most shell is called the valence shell, and the electrons in that energy shell are called valence electrons. It is the number of valence electrons that determine how reactive an element is and how it will form bonds with other elements.

5. Ions continued An ion is an atom, or group of atoms, that has gained or lost one or more electrons. Ions are also referred to as charged particles.

6. Sodium Sodium is an atom that has only one electron in it’s outermost shell. The quickest way for it to become stable is to donate an electron, which it does easily. When sodium loses an electron it becomes a positively charged ion since it will now have one more proton than it does electrons.

7. Chlorine Chlorine is at the opposite end of the spectrum as sodium. Chlorine has 7 electrons in it’s valence shell, so for it to be most stable it needs to accept an electron. When it does this, it becomes a negatively charged ion since it has one more electron than it has protons.

8. Sodium meets chlorine..a love story. Since we now know that sodium (Na) easily donates an electron, and that chlorine (Cl) easily accepts an electron, lets see what happens when they meet. ionic bonding

9. Covalent bonding. A second type of bonding is called covalent bonding. In covalent bonding instead of transferring electrons from one atom to another, the atoms share electrons. It is this type of bonding that forms molecules.

10. Water Water is formed by the covalent bonding between one oxygen atom and two hydrogen atoms. Oxygen has 6 electrons in it’s valence shell, so it needs to add 2 more to be most stable. Hydrogen as 1 valence electron, so it needs to add 1 more to be most stable.

11. Forming a water molecule. covalent bonding to make water So in summary In ionic bonding one or more electrons is transferred between atoms resulting in ions. These ions are held together by electrostatic force. In covalent bonding, electrons are shared between two or more atoms, forming a molecule.

12. More bonding animations. ionic and covalent bonding animations

13. Isotopes. Isotopes are atoms of elements that have the same atomic number, but different mass numbers. This is due to extra neutrons present in the nucleus. Carbon normally has an mass number of 12, but there exists in nature a second form of carbon that has a mass number of 14. Carbon 14 is a radioactive isotope used in the process called carbon dating.

14. Isotopes In all other respects, isotopes of an element react with other elements the same way. An example of this is the formation of heavy water. Hydrogen, the simplest of atoms contains one proton, one electron and zero neutrons in it’s most common form. (Atomic #=1; Mass #=1) There are two naturally occurring isotopes of hydrogen, one of them is called deuterium and it has one proton, one electron and one neutron. (Atomic # =1; Mass #=2).

15. Heavy water Deuterium bonds with oxygen atoms just like regular hydrogen atoms. What results is called heavy water. Heavy water has slightly different physical characteristics as regular water. Heavy water is used in the cooling towers of nuclear power plants.

16. Radioactivity Some isotopes are unstable and deteriorate into a different element all together. Carbon 14 decays into nitrogen. When they decay, some isotopes emit radioactive particles. These are called radioactive isotopes and can cause health problems.

17. Questions. When Sodium (Na) donates an electron to Chlorine (Cl) what charge will the resulting Sodium ion have? What charge will the resulting Chlorine ion have? How is Carbon 14 different than Carbon 12? Which type of bonding results in the formation of molecules?