Chapter 6: The Periodic Table

Transcription

1 Chapter summary 6:1 History od the Periodic table 1) Mendeleev s Periodic table 2) Problems with early periodic tables Chapter 6: The Periodic Table 6:2 Modern Periodic table 1) Key points: Periodic law, Periods and Groups, 3 broad classes of elements 2) Properties of the 3 classes of elements (Metals, nonmetals and metalloids) 3) Sorting elements based on general properties (3-types) 4) Sorting elements based on electron configuration (4-types) 5) Periodic trends: a) Atomic size b) Ionization energy c) Ionic size d) Electronegativity Chemistry _ Notes Dr. Chirie Sumanasekera 10 /30/ 2017

2 6.1: History of the periodic table 1) 2) Mendeleev s Periodic table Problems with early periodic tables

3 History: Mendeleev s periodic table For thousands of years only a few elements were known - Gold, Silver and copper As chemists began using the scientific method, the rate of discovery of elements increased Chemists used the properties of elements to sort them into groups. In 1869 Dimitri Mendeleev organized the known elements into groups based on repeating properties and increasing atomic mass Mendeleev left spaces for elements still not discovered (?) as he predicted their properties and discovery In the late 1800s Gallium & Germanium which has properties similar to Mendeleev s predictions for elements between Zn and As were discovered. Then his periodic table gained acceptance. Mendeleev s published periodic table from 1869

4 History: Problems with early periodic tables When Mendeleev created his periodic table, scientists did not know about a) the structure of the atom or b) that atoms of each element had a unique number of protons (atomic number) Number of protons is the same in all isotopes of an element. Proton numbers are different only between different elements So arranging elements based on atomic mass- the sum of protons and neutronsis not a good way to arrange elements based on their properties as it ignores the elements with chemically similar isotopes A better way to groups elements is by Atomic number which is unique to each element.

5 6.2: The Modern Periodic Table

6 Modern Periodic Table: Organization of Elements Group: Period: 1 2 Metals Metalloids Nonmetals Figure 6.5 (p:158) 18

7 1) Key Points on the arrangement of Elements: 1) Arranged in order of increasing atomic number (protons) 2) 7 periods and 18 groups /columns 3) Each period represents a Principle Energy Level (n=1 to n=7) 4) More elements in higher numbered periods because there are more orbitals in those energy levels 5) Elements within a group have similar properties 6) Properties of elements in a period change as you go from left to right but the properties within a period repeat as you move from one to another period 7) Three broad classes of elements: majority of the elements are metals (left side), some are nonmetals (upper right) and in between these are a few metalloids 8) Across a period elements become less metallic Periodic law: When elements are arranged in order f increasing atomic number there is a periodic repetition of their physical and chemical properties

8 *Noble gases: He, Ne, Ar, Kr, Xe, Rn **Ductile = make into wires 2) properties of the3 classes of Elements 1. Metals 2. Metalloids 3. Non metals Percent of elements 80% 6% 14% Heat conduction Excellent poor Mostly very poor Electrical conduction Excellent Poor (silicon chips made of mixtures of Si and B conduct well) Mostly very poor At room Temperature: All Solid (except Hg) All solid Some are solid, gas (H, He, N, O, F, Cl and all noble gases*) and Br is a brown liquid **Ductile and malleable yes no no High luster/sheen Yes no Not really Toughness Usually hard soft Range from hard to soft In general: All have similar properties Has both metal and non metal properties Malleable = can be hammered into shape Has the opposite properties of Metals and this group has great variation in properties

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