CHEMISTRY of LIFE

1. CHEMISTRY of LIFE Ch 2.1

2. Composition of Matter • Matter - Everything in universe is composed of matter • Matter is anything that occupies space or has mass • Mass – quantity of matter an object has • Weight – pull of gravity on an object

3. Questions Is weight and mass the same thing? Would I weigh more on the moon or on Earth? Is my mass the same on the moon and on Earth?

4. Elements • Pure substances that cannot be broken down chemically into simpler kinds of matter • More than 100 elements (92 naturally occurring)

5. Each element unique chemical symbol • Consists of 1-2 letters • First letter is always capitalized

6. 90% of the mass of an organism is composed of just 4 elements • oxygen • carbon • hydrogen • nitrogen

7. Atoms • An Atom is the simplest particle of an element that retains all the properties of that element • Properties of atoms determine the structure and properties of the matter they compose

8. Do you know? • All matter is made up of atoms • Atoms are the smallest part of a substance that is still that substance • Atoms are very, very small

9. The Nucleus • Central core of the atom • Consists of positive charged protons and neutral neutrons • Positively charged • Contains most of the mass of the atom

10. The Protons • All atoms of a given element have the same number of protons • Number of protons called the atomic number • Protons and electrons are equal to create a neutral element

11. Periodic table on back cover or page 1086 Practice • Atomic number of oxygen (O) • 8 • Atomic number of zinc (Zn) • 30 • # protons in bromine (Br) • 35 • protons in gold (Au) • 79 • Element with 44 protons • Ruthenium (RU)

12. The Neutrons • The number varies slightly among atoms of the same element • Different number of neutrons produces isotopes of the same element

13. Isotopes • Isotopes of the same element have the same chemical properties • Because they have the same number of electrons! • Some isotopes are radioactive • Unstable and break down at a constant rate • Used to treat cancer, determine the ages of rocks and fossils, kill bacteria, as molecular labels

14. Atomic Mass • Protons & neutrons are found in the nucleus of an atom • Protons and neutrons each have a mass of 1 amu (atomic mass unit) • The atomic mass of an atom is found by adding the number of protons & neutrons in an atom

15. The Electrons • Negatively charged high energy particles with little or no mass • Travel at very high speeds at various distances (energy levels) from the nucleus

16. Electrons in the same energy level are approximately the same distance from the nucleus • Outer energy levels have more energy than inner levels • Each level holds only a certain number of electrons

17. Energy Levels • Octet Rule – except for the first shell which is full with two electrons, atoms interact in a manner to have eight electrons in their valence (outermost) shell

18. Chemically Inert Elements • Inert elements have their outermost energy level fully occupied by electrons Figure 2.4a

19. Chemically Reactive Elements • Reactive elements do not have their outermost energy level fully occupied by electrons Figure 2.4b

20. Periodic Table • Elements are arranged by their atomic number on the Periodic Table • The horizontal rows are called Periods & tell the number of energy levels • Vertical groups are called Families & tell the outermost number of electrons

22. Compounds • Most elements do not exist by themselves • Readily combine with other elements

23. A compound is a pure substance made up of atoms of two or more elements in a fixed proportion • Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound H2O

24. Chemical Formulas • Subscript after a symbol tell the number of atoms of each element • H20 has 2 atoms of hydrogen & 1 atom of oxygen • Coefficients before a formula tell the number of molecules • 3O2represents 3 molecules of oxygen or (3x2) or 6 atoms of oxygen

25. The physical and chemical properties of a compound differ from the physical and chemical properties of the individual elements that compose it

26. Sodium (Na) is a silver colored metal soft enough to cut with a knife. It reacts explosively with water Chlorine is a poisonous, greenish gas that was used to kill many soldiers in WWI Sodium and chlorine combine to form the compound sodium chloride that is safe for us to eat - – Table Salt

27. The tendency of elements to combine and form compounds depends on the number and arrangement of electrons in their outermost energy level • Atoms are most stable when their outer most energy level is filled

28. Most atoms are not stable in their natural state • Tend to react with other atoms in order to become more stable • In chemical reactions bonds are broken; atoms rearranged and new chemical bonds are formed

29. Covalent Bonds • Formed when two atoms share one or more pairs of electrons Compounds formed by covalent bonds are called MOLECULAR COMPOUNDS or MOLECULES

30. (–) O H H (+) From: http://ghs.gresham.k12.or.us/science /ps/sci/ibbio/chem/notes/chpt2/water.htm Polar Molecules • Unequal sharing of electrons • Have a slight electrical charge on either side of the molecule 105O • H2O • Polar molecules dissolve in water • Hydrogen bonding

31. Nonpolar molecules • No unequal sharing • Do not dissolve in water • Oils and fats

32. Ionic Bonds • Some atoms become stable by losing or gaining electrons • Atoms that lose electrons are called positive ions or Cations Compounds that from ionic bonds are called IONIC COMPOUNDS

33. Atoms that gain electrons are called negative ions or Anions • Because positive and negative electrical charges attract each other ionic bonds form

34. What word means: • To clarify with examples • Illustrate • To draw a conclusion by reasoning; to speculate • Infer

35. What word means: • Discuss good and bad points, strenths, & weaknesses, judge worth or quality • Evaluate • To give facts that make clear, to make known in detail • Explain

36. Quiz!