Periodic Table. Chapter 19, Section 3

Transcription

1 Periodic Table Chapter 19, Section 3

2 3 The Periodic Table Organizing the Elements Periodic means repeated in a pattern. In the late 1800s, Dmitri Mendeleev, a Russian chemist, searched for a way to organize the elements. When he arranged all the elements known at that time in order of increasing atomic masses, he discovered a pattern.

3 3 The Periodic Table Mendeleev s Predictions Mendeleev had to leave blank spaces in his periodic table to keep the elements properly lined up according to their chemical properties. He looked at the properties and atomic masses of the elements surrounding these blank spaces.

4 3 The Periodic Table Mendeleev s Predictions From this information, he was able to predict the properties and the mass numbers of new elements that had not yet been discovered.

5 3 The Periodic Table Mendeleev s Predictions This table shows Mendeleev s predicted properties for germanium, which he called ekasilicon. His predictions proved to be accurate.

6 3 The Periodic Table Improving the Periodic Table On Mendeleev s table, the atomic mass gradually increased from left to right. If you look at the modern periodic table, you will see several examples, such as cobalt and nickel, where the mass decreases from left to right.

7 3 The Periodic Table Improving the Periodic Table In 1913, the work of Henry G.J. Moseley, a young English scientist, led to the arrangement of elements based on their increasing atomic numbers instead of an arrangement based on atomic masses. The current periodic table uses Moseley s arrangement of the elements.

8 3 The Periodic Table Organizing the Elements In today s periodic table, the elements are arranged by increasing atomic number and by changes in physical and chemical properties.

9 3 The Periodic Table Regions on the Periodic Table The periodic table has several regions with specific names. The horizontal rows of elements on the periodic table are called periods. The elements increase by one proton and one electron as you go from left to right in a period.

10 3 The Periodic Table The Atom and the Periodic Table The vertical columns in the periodic table are called groups, or families, and are numbered 1 through 18. Elements in each group have similar properties.

11 3 The Periodic Table Electron Cloud Structure In a neutral atom, the number of electrons is equal to the number of protons. Therefore, a carbon atom, with an atomic number of six, has six protons and six electrons.

12 3 The Periodic Table Electron Cloud Structure Scientists have found that electrons within the electron cloud have different amounts of energy.

13 3 The Periodic Table Electron Cloud Structure Scientists model the energy differences of the electrons by placing the electrons in energy levels.

14 3 The Periodic Table Electron Cloud Structure Energy levels nearer the nucleus have lower energy than those levels that are farther away. Electrons fill these energy levels from the inner levels (closer to the nucleus) to the outer levels (farther from the nucleus).

15 3 The Periodic Table Electron Cloud Structure Elements that are in the same group have the same number of electrons in their outer energy level. There is a special phrase we use for the outer energy electrons valence electrons Elements are most stable when their outer energy level is full.

16 3 The Periodic Table Electron Cloud Structure Elements that are in the same group have the same number of electrons in their outer energy level. It is the number of electrons in the outer energy level that determines the chemical properties of the element.

17 3 The Periodic Table Electron Dot Diagrams Elements that are in the same group have the same number of electrons in their outer energy level. These outer electrons are so important in determining the chemical properties of an element that a special way to represent them has been developed.

18 3 The Periodic Table Electron Dot Diagrams An electron dot diagram uses the symbol of the element and dots to represent the electrons in the outer energy level. Electron dot diagrams are used also to show how the electrons in the outer energy level are bonded when elements combine to form compounds.

19 3 The Periodic Table Same Group Similar Properties The elements in Group 17 (or VIIA) have electron dot diagrams similar to chlorine. All elements in this group have seven electrons in their outer energy levels.

20 3 The Periodic Table Same Group Similar Properties Not all elements will combine readily with other elements. The elements in Group 18 (or VIIIA) have complete outer energy levels. This special configuration makes Group 18 elements relatively unreactive.

21 Periodic Table Most elements are metals and occur on the left side. The nonmetals appear on the right side. Metalloids are elements that have some metallic and some nonmetallic properties.

22 Physical Properties of Metals ÜHave Luster -shiny Ü Are Conductors -heat and electricity move through them easily ÜMalleable Can be hammered into a different shape ÜDuctile Can be drawn into a wire ÜHigh Density Heavy for their size ÜMetals are solid, except for mercury

23 Examples of Metals

24 Physical Properties of NonMetals ÜDull not shiny ÜNonconductors heat and electricity do not move through easily ÜBrittle break easily ÜMost nonmetals are gases at room temperature

25 Examples of Non-Metals Nitrogen

26 Metal: Elements that are usually solids at room temperature. Most elements are metals. Non-Metal: Elements in the upper right corner of the periodic table. Their chemical and physical properties are different from metals. Metalloid: Elements that lie on a diagonal line between the metals and non-metals. Their chemical and physical properties are intermediate between the two.

27 Lets Classify! Silver Iron Oxygen Calcium Carbon Sulfur Aluminum Sodium

28 Valence Electrons, and Lewis Electron Dot Structures, and the Periodic Table We always have so much to do!

29

30 Practice! Find the number of valence electrons for: 1. Li 2. P 3. I 4. Ar 5. Ca 6. O

31 Check It! 1. Li = 1 2. P = 5 3. I = 7 4. Ar = 8 5. Ca = 2 6. O = 6

32 Now What Do I Do With That? We can use number of valence electrons to predict which charge they make when we turn them into an ion. Review: what s an ion?? An atom that has gained or lost electrons. Atoms can become more stable if they have FULL outer energy levels Octet Rule: most atoms want to be surrounded by 8 valence electrons or 0 valence electrons. (It s all or nothing)

33 How So? For atoms with LESS than 4 valence electrons, they re going to lose/give up electrons to form positive cations. For atoms with MORE than 4 valence electrons, they re going to gain/steal electrons to form negative anions. For atoms with 4 valence electrons, it can go either way. For atoms with 8 valence electrons, there is no change.

34 Example I need to know what ion Aluminum forms. I know that it has 3 valence electrons. Is 3 closer to 0 or 8? Closer to 0 So will it gain or lose electrons? Lose How many will it lose to be 0? All 3 If it loses electrons, will it be + or -? So I end up with Al +3 +

35 When an atom or molecule gain or loses an electron it becomes an ion. A cation has lost a(n) electron(s) and therefore has a positive charge An anion has gained a(n) electron(s) and therefore has a negative charge.

36 PREDICTING ION CHARGES In general metals (like Mg) lose electrons ---> cations nonmetals (like F) gain electrons ---> anions

37 More Practice! Predict the ion formed by the following elements: Write the symbol with the charge. 1. Cl 2. B 3. K 4. Ca 5. O 6. Ne

38 Check It! 1. Cl = Cl - 2. B = B K = K + 4. Ca = Ca O = O Ne = Ne (no change)

39 Now For Lewis Dot Structures! (Also called Electron Dot Structures) Step 1: Write the symbol for the element. Step 2: Put dots around the symbol to represent valence electrons.

40 See It In Action! Let s do Carbon. The symbol for carbon is C Carbon is in Group 4 = 4 valance electrons Put one on each side!

41 Rules for filling in Dots Maximum 2 dots per side (4 sides = 8 dots) It does not matter which side you start on. You have to fill in each side with one dot before you double up Example: Sulfur has how many valence e -? 6 How many dots does it get? 6 S

42 You do some! Draw the Lewis Dot Structures for the following atoms: 1. Oxygen 2. Sodium 3. Fluorine 4. Nitrogen 5. Beryllium

43 Check It! O Na F N Be

44 Across Period 2

45 Electron Dot, or Lewis Dot Symbols for the Representative Elements Since elements in the same family have the same number of valence electrons, their dot structures will look the same, too!

46 Ion Formation Summary n Atoms gain or lose electrons to become more stable. They achieve the same number of valence electrons as the Noble Gases (in the last column)