Chemistry—A Quick Review

1. Chemistry—A Quick Review • Matter—takes up space and has mass • Element—can’t be broken down into other substances • 25 elements are essential to life • C, O, H, & N make up 96% of living matter • Compound-consists of 2 or more elements • in a fixed ratio How do compounds (like NaCl) have emergent properties?

2. Atom—smallest part of an element that still • has the properties of that element • Atoms are made of • Neutrons (neutral!) in the • Protons (+) nucleus • Electrons (-) Neutrons and protons each have a mass of about 1 Dalton (D) The mass of an electron is so small that it’s negligible

3. This is a helium atom—count the protons, neutrons, and electrons! 

4. Atomic number--# of protons (identifies an element) Mass number--# of protons + # of neutrons ( aka. atomic mass or atomic weight) Na 11 23

5. There are the same number of electrons as protons in an atom. What do the elements in each row have in common? Each column?

6. Isotopes—elements that have different #s of neutrons ex. 12C, 13C, and 14C Radioactive isotopes—the nucleus decays to give off energy and particles --useful in dating of fossils and as tracers But…radiation from decaying isotopes is also harmful!

7. The electrons in atoms have different amounts of energy. Energy = ability to do work Potential energy is energy that’s stored. Electrons can jump from one level to another if they gain or lose energy. 8 8 2

8. Electrons spend most of their time in orbitals.

9. We need to know how many electrons an atom has in its outermost shell since those pretty much determine how it behaves. The electrons in the outermost shell are called VALENCE ELECTRONS. If the valence shell is filled, the atom is unreactive(inert). Unfilled valence shells WANT to be filled!

10. Atoms fill their valence shells by bonding • with other atoms. • Types of bonds: • Covalent (sharing!) • Polar vs. Nonpolar • Ionic (Give and take) • Hydrogen • Van der Waals interactions

11. Atoms share equally in nonpolar covalent bonds. They share unequally in polar covalent bonds because more electronegative atoms want electrons more. Which of these are polar? Which are nonpolar?

12. In ionic bonds, the more electronegative atom grabs the electrons from the less electronegative atom. Each becomes an ion (charged particle), and the opposite charges hold the ions together.

13. Water molecules are held together by weak bonds called hydrogen bonds

14. Hydrogen bonds form between a partially positive hydrogen and an electronegative atom like this N in ammonia.

15. van der Waals interactions occur between constantly changing charged parts of molecules. Although hydrogen bonds and van der Waals interactions are weak, the sum total of all the interactions can be very strong.

16. Function is related to shape…is that a theme?! Shape is important since molecules need to recognize each other.

17. Molecules that have the same shape can have the same function.

18. If you were a pharmaceutical researcher, why would you want to learn the three-dimensional shapes of naturally occurring signaling molecules?

19. Chemical reactions—making and breaking of chemical bonds Reactants—starting materials Products—end materials 6CO2 + 6H2O + light  C6H12O6 + 6O2

20. Most reactions are reversible. Dynamic equilibrium is when the rate of the forward reaction is equal to the rate of the backward reaction. 3H2 + N2 2NH3 Which type of chemical reaction occurs faster at equilibrium, the formation of products from reactants or reactants from products?