Wednesday September 12 th,

Transcription

1 Wednesday September 12 th, Today: Small Review Quiz Chapter Frequency: CD

2 Classification of Matter Matter is organized by its components: elements, compounds, and mixtures.

3 A Comparison of Solids, Liquids, and Gases Chapter 2, Section 4 3

4 Summary of Chemical and Physical Properties and Changes

5 Change of State: Solid and Liquid Liquid and Gas Solid and Gas 5

6 Questions?

7 Quiz #2

8 Chapter 3 Atoms and Elements 8

9 Elements Elements are pure substances from which all other things are built. gold carbon aluminum 9

10 Symbols of Elements A symbol represents the name of an element. consists of 1 or 2 letters. starts with a capital letter. Examples: 1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogen Ca calcium F fluorine Al aluminum O oxygen Mg magnesium

11 Symbols of Common Elements Symbols of some common elements: S, sulfur Au, gold Al, aluminum Ag, silver

12 Periodic Table 12 12

13 Periods and Groups On the periodic table, groups contain elements with similar properties and are arranged in vertical columns ordered from left to right. periods are the horizontal rows of elements, and they are counted from the top as Period 1 to Period 7.

14 Periods and Groups

15 Group Numbers Group numbers use numbers to identify the columns from left to right. the letter A for the representative elements (1A to 8A) and the letter B for the transition elements. The representative elements include the first 2 groups, 1A (1) and 2A (2), in addition to groups 3A (13), 4A (14), 5A (15), 6A (16), 7A (17), and 8A (18).

16 Alkali Metals Group 1A (1), the alkali metals, includes lithium sodium, potassium, rubidium and cesium. The reactivity of these elements increases from the top to bottom of the group.

17 Halogens Group 7A (17), the halogens, includes fluorine, chlorine, bromine, iodine, and astatine. Fluorine and chlorine are highly reactive

18 Nobel Gases Group 8A (18) is the nobel gases, which include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Ra). Nobel gas elements are unreactive and are seldom found in combination with other elements.

19 Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. Metals (blue) are located to the left. Nonmetals (yellow) are located to the right. Metalloids (green) are located along the heavy zigzag line between the metals and nonmetals

20 Properties of Metals, Nonmetals, and Metalloids Metals are shiny and ductile. good conductors of heat and electricity. Nonmetals are not especially shiny, ductile, or malleable. poor conductors of heat and electricity. Metalloids are better conductors than nonmetals, but not as good as metals. used as semiconductors and insulators.

21 Dalton s Atomic Theory Dalton theorized that Atoms are tiny particles of matter too small to see, are able to combine with other atoms to make compounds, and are similar to each other for each element and different from atoms of other elements. A chemical reaction is the rearrangement of atoms. Images of nickel atoms are produced when nickel is magnified millions of times by a scanning tunneling microscope (STM). This instrument generates an image of the atomic structure.

22 Subatomic Particles Atoms contain subatomic particles such as Protons, which have a positive (+) charge; electrons, which have a negative ( ) charge; and neutrons, which have no charge. Experiments show that like charges repel and unlike charges attract. 22

23 Rutherford s Gold-Foil Experiment In Rutherford s gold-foil experiment, positively charged particles were aimed at atoms of gold and most went straight through the atoms, but some were deflected only occasionally. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.

24 Rutherford s Gold-Foil Experiment (a) Positive particles are aimed at a piece of gold foil. (b) Particles that come close to the atomic nuclei of gold are deflected from their straight path.

25 Structure of the Atom An atom consists of a nucleus that contains protons and neutrons, and electrons in a large, empty space around the nucleus. 25

26 Atomic Mass Scale On the atomic mass scale for subatomic particles, 1 atomic mass unit (amu) is defined as 1/12 of the mass of the carbon-12 atom. Therefore, a proton has a mass of about 1 (1.007) amu. a neutron has a mass of about 1 (1.008) amu. an electron has a very small mass, amu.

27 Atomic Number The atomic number is specific for each element. is the same for all atoms of an element. is equal to the number of protons in an atom. appears above the symbol of an element in the periodic table. Atomic Number Symbol 11 Na

28 Atomic Number and Protons Each element has a unique atomic number equal to the number of protons: Hydrogen has atomic number 1; every H atom has one proton. Carbon has atomic number 6; every C atom has six protons. Copper has atomic number 29; every Cu atom has 29 protons.

29 Learning Check State the number of protons in each of the following: 1. A nitrogen atom A. 5 protons B. 7 protons C. 14 protons 2. A sulfur atom A. 32 protons B. 16 protons C. 6 protons 3. A barium atom A. 137 protons B. 81 protons C. 56 protons

30 Solution State the number of protons in each of the following: 1. A nitrogen atom B. 7 protons 2. A sulfur atom B. 16 protons 3. A barium atom C. 56 protons

31 Number of Electrons in an Atom All atoms of an element are electrically neutral; they have a net charge of zero. an equal number of protons and electrons. Number of protons = Number of electrons Example: Aluminum atoms have 13 protons and 13 electrons; the net charge is zero.

32 Mass Number The mass number represents the number of subatomic particles in the nucleus, which is equal to the sum of the number of protons + number of neutrons. Since protons and neutrons account for the majority of mass in an atom, we call this the mass number.

33 Atomic Models

34 Learning Check An atom of zinc has a mass number of How many protons are in a zinc atom? A. 30 B. 35 C How many neutrons are in a zinc atom? A. 30 B. 35 C. 65

35 Learning Check An atom has 14 protons and 20 neutrons. 1. What is its atomic number? A. 14 B. 20 C What is its mass number? A. 14 B. 20 C What is this element? A. Si B. Ca C. Ar

36 Isotopes Isotopes are atoms of the same element that have different mass numbers. have the same number of protons but different numbers of neutrons. can be distinguished by atomic symbols.

37 Isotopes and Mass and Atomic Symbols Since each isotope of an element has a different number of neutrons, each isotope s mass number will be different. We write these as atomic symbols: Mass numbers are in the upper left corner. Atomic numbers are in the lower left corner. Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number atomic number 23 Na 11

38 Atomic Symbols For an atom, the atomic symbol gives the number of protons (p + ), neutrons (n), and electrons (e ) O P Zn 8 p + 15 p + 30 p + 8 n 16 n 35 n 8 e 15 e 30 e

39 Learning Check Naturally occurring carbon consists of three isotopes: C-12, C-13, and C-14. State the number of protons, neutrons, and electrons in each of the following. 12 C 13 C 14 C Protons Neutrons Electrons

40 Friday Finish Chapter 3 In Class Group Work