2. Chapter 2a Notes Chemistry Prentice Hall pp. 34-43 Pre AP Biology

3. What’s the Matter? Matter- anything that has mass and takes up space; trees, books, etc. NOT heat, gravity, etc. All of the materials around you are made up of matter. You are made up of matter, as are the chair you sit on and the air you breathe. 1. Give an example of solid matter. 2. Give an example of liquid matter. 3. Give an example of gaseous matter. 4. Is all matter visible? 5. Does all matter take up space?

4. Atoms: The Building Blocks of Elements An atom is the smallest particle of an element that has the characteristics of that element. Atoms are the basic building blocks of all matter. The structure of an atom Atoms are made of protons, neutrons and electrons –The center of an atom is called the nucleus All nuclei contain positively charged particles called protons (p + ). Most contain particles that have no charge, called neutrons (n 0 ).

5. The Structure of an atom The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e - ) Because opposites attract, the negatively charged electrons are held in the electron cloud by the positively charged nucleus. This region of space is referred to as an electron cloud. Nucleus (protons & neutrons) Electron energy levels (e-)

6. Electron energy levels Electrons exist around the nucleus in regions known as energy levels. The first energy level can hold only two electrons. The second level can hold a maximum of eight electrons. The third level can hold up to 18 electrons. Atoms contain equal numbers of electrons and protons; therefore, they have no net charge. Nucleus 8 neutrons (n 0 ) Oxygen atom 8 protons (p+)

7. Elements Everything – whether it is a rock, frog, or flower – is made of substances called elements. An element is a substance that can’t be broken down into simpler chemical substances

8. Natural elements in living things Of the naturally occurring elements on Earth, only about 25 are essential to living organisms. Trace elements such as iron and copper, play a vital role in maintaining healthy cells in all organisms. Plants obtain trace elements by absorbing them through their roots; animals get them from the foods they eat. Table 6.1 Some Elements That Make Up the Human Body ElementSymbol Percent By Mass in Human Body Element Symbol Percent By Mass in Human Body Molybdenum Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Sodium Chlorine Magnesium Selenium Iron Zinc Copper Iodine Manganese Boron Chromium Cobalt Fluorine O C H N Ca P K S Na Cl Mg 65.0 18.5 9.5 3.3 1.5 1.0 0.4 0.3 0.2 0.1 Fe Zn Cu I Mn B Cr Mo Co Se F trace Carbon, hydrogen, oxygen, and nitrogen make up more than 96 percent of the mass of a human body.

9. 6 C Carbon 12.011 Characteristics of Elements  Atomic number- the number of protons in an element; the elements are arranged on the periodic table in order of increasing atomic number  Mass number- the # of protons + neutrons  Ex. Helium atoms have 2 P and 2 N = mass # of 4  Ex. # of neutrons = mass #-atomic # Atomic # Mass # An Element in the Periodic Table 2 He Helium 4.0 Mass # Atomic Number

10. The Periodic Table Elements in the same vertical column have similar properties because these elements have the same number of electrons in their outer energy levels. For example, Mg and Ba both have 2e- in their outer energy levels. 18 Families Vertical Columns 7 Rows or Periods

11. Isotopes of an Element Atoms of the same element always have the same number of protons but may contain different numbers of neutrons. Atoms of the same element that have different numbers of neutrons are called isotopes of that element. Because they have the same number of electrons, all isotopes have the same chemical properties. Nonradioactive carbon-12Nonradioactive carbon-13Radioactive carbon-14 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 8 neutrons 6 electrons 6 protons 7 neutrons Figure 2-2 Isotopes of Carbon

12. Radioactive Isotopes The nuclei of some isotopes are unstable The unstable nuclei break down at a constant rate over time As they break down, they give off dangerous radiation Radioactive isotopes can be used for many different scientific purposes: –Determine the age of rocks and fossils –Treat cancer –Kill bacteria that causes food spoilage –Label substances within organisms to track movement or growth (tracers)

13. Chemical Compounds In nature, most element are found combined with other elements A compound is a substance that is composed of atoms of two or more different elements that are chemically combined in a definite proportion. Ex. Water = H 2 O = 2 H for every 1 Oxygen -“H 2 O” is a chemical formula that names the kind and number of atoms in the compound Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms. For many elements, an atom becomes stable when its outermost energy level is full.

14. Chemical Bonding  Compounds can be broken down into elements  Physical properties of elements change when they form compounds Table salt (NaCl) is a compound composed of the elements sodium and chlorine.  Ex. Na = sodium = shiny metal + Cl = chlorine = green gas NaCl = sodium chloride = table salt  Atoms in compounds are held together with chemical bonds –Two main types of chemical bonds –Ionic –Covalent

15. Figure 2-3 Ionic Bonding Sodium atom (Na)Chlorine atom (Cl)Sodium ion (Na + )Chloride ion (Cl - ) Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1 How ionic bonds form An atom (or group of atoms) that gains or loses electrons has an electrical charge and is called an ion. An ion is a charged particle made of atoms. The attractive force between two ions of opposite charge is known as an ionic bond.

16. Sodium atom (Na)Chlorine atom (Cl)Sodium ion (Na + )Chloride ion (Cl - ) Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1 Figure 2-3 Ionic Bonding

17. How covalent bonds form Sharing electrons with other atoms is another way for elements to become stable. Two hydrogen atoms can combine with each other by sharing their electrons. Each atom becomes stable by sharing its electron with the other atom. The attraction of the positively charged nuclei for the shared, negatively charged electrons holds the atoms together. A covalent bond holds the two hydrogen atoms together. Hydrogen molecule

18. Molecules A molecule is a group of atoms held together by covalent bonds. Water molecule

19. Chemical Reactions Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances. All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism. Writing chemical equations In a chemical reaction, substances that undergo chemical reactions, are called reactants. Substances formed by chemical reactions, are called products. A molecule of table sugar can be represented by the formula: C 12 H 22 O 11. The easiest way to understand chemical equations is to know that atoms are neither created nor destroyed in chemical reactions. They are simply rearranged.

20. Water, Water Everywhere If you have ever seen a photograph of Earth from space, you know that much of the planet is covered by water. Water makes life on Earth possible. If life as we know it exists on some other planet, water must be present to support that life.

21. Water and Its Importance Water is perhaps the most important compound in living organisms. Water makes up 70 to 95 percent of most organisms.

22. Water is Polar Sometimes, when atoms form covalent bonds they do not share the electrons equally. This is called a polar bond. A polar molecule is a molecule with an unequal distribution of charge; that is, each molecule has a positive end and a negative end. Water is an example of a polar molecule. Water can dissolve many ionic compounds, such as salt, and many other polar molecules, such as sugar. Water molecules also attract other water molecules. Weak hydrogen bonds are formed between positively charged hydrogen atoms and negatively charged oxygen atoms.

23. Water resists temperature changes Water resists changes in temperature. Therefore, water requires more heat to increase its temperature than do most other common liquids. Water expands when it freezes Water is one of the few substances that expands when it freezes. Ice is less dense than liquid water so it floats as it forms in a body of water.

24. Hydrogen Bonds Polar molecules have partial (+) and (-) charges that attract each other Cohesion- attraction between molecules of the same substance; ex: drops of water bead on smooth surfaces (water is attracted to itself), surface tension Adhesion- attraction between molecules of different substances; ex: meniscus of graduated cylinder, capillary action

25. Hydrogen Bonds http://www.northland.cc.mn.us/biology/Bi ology1111/animations/hydrogenbonds.ht mlhttp://www.northland.cc.mn.us/biology/Bi ology1111/animations/hydrogenbonds.ht ml

26. Mixtures and Solutions A mixture is a material composed of two or more elements or compounds that are physically mixed together, but not chemically bonded. In a mixture of substances, the individual components retain their own properties. (Neither component of the mixture changes.) A solution is a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent). Sugar molecules in a powdered drink mix dissolve easily in water to form a solution.

27. Cl - Water Cl - Na + Water Na + Figure 2-9 NaCI Solution

28. Cl - Water Cl - Na + Water Na +

29. Suspensions Some molecules do not dissolve in water, but separate into pieces so small, they do not settle (water hold pieces up) Mixtures of water and nondissolved molecules are known as suspensions Although blood contains many particles that are dissolved, it also carries nondissolved particles throughout the body (suspension)

30. Acids, Bases, and pH The pH is a measure of how acidic or basic a solution is. A scale with values ranging from below 0 to above 14 is used to measure pH. Substances with a pH below 7 are acidic. An acid is any substance that forms hydrogen ions (H+) in water. A solution is neutral if its pH equals 7. Substances with a pH above 7 are basic. A base is any substance that forms hydroxide ions (OH-) in water. Buffers are weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH. More acidic NeutralMore basic pH 11

31. Oven cleaner Bleach Ammonia solution Soap Sea water Human blood Pure water Milk Normal rainfall Acid rain Tomato juice Lemon juice Stomach acid Neutral Increasingly Basic Increasingly Acidic pH Scale