SNC2D CHEMISTRY CHEMICAL REACTIONS L (P.146-148) Dmitri Mendeleev & The Periodic Table The periodic table contains a standard set of symbols to represent the elements, laid out in a specific pattern. It is based on the organization developed by the Russian scientist Dmitri Mendeleev in 1869. He was the first person to create a table that organized all 64 elements known at that time, including those that had not yet been discovered yet. His periodic table made the study of chemistry manageable! February 10, 2013 2DCHEM - 1 The Modern Periodic Table February 10, 2013 2DCHEM - 2 1
Scientists have discovered that there are patterns among the elements. If they are arranged in a certain order, elements with similar properties all line up in the same column. This arrangement of elements is called the periodic table. February 10, 2013 2DCHEM - 3 Most elements are metals and are located on the left and centre of the periodic table. A few (about 20%) are non-metals. With the exception of hydrogen, all non-metals are located on the right side of the table. The boundary between metals and non-metals is a zigzag line (i.e. metalloids). February 10, 2013 2DCHEM - 4 Hydrogen has its own unique colour on the periodic table because it does not fit neatly into any of the other categories. It has the properties of nonmetals but its electron arrangement resembles that of the Group 1 elements. February 10, 2013 2DCHEM - 5 2
Elements are organized on the periodic table according to atomic number and properties. Each column is a group or family of elements. The elements in each group (i.e. chemical family) have similar physical and chemical properties. Each row of elements is called a period. February 10, 2013 2DCHEM - 6 PERIODIC TABLE structured arrangement of elements metals(left) and non-metals(right) separated by metalloids (zigzag) GROUP(FAMILY) a column of elements on the periodic table with similar properties PERIOD a row on the periodic table NOTE! Hydrogen behaves mostly as a non-metal. February 10, 2013 2DCHEM - 7 PRACTICE 1. Classifyeach of the following as either a metal or a non-metal: (a) oxygen (b) sodium (c) chlorine (d) gold (e) zinc non-metal metal non-metal metal metal February 10, 2013 2DCHEM - 8 3
PRACTICE 2. Can all elements on the periodic table be classified as metals or nonmetals? Explain. no some elements, known as metalloids (green squares near the zigzag line) have properties that are in-between metals and non-metals February 10, 2013 2DCHEM - 9 Bohr-Rutherford Diagrams RECALL! We can combine Rutherford s nuclear model with Bohr s planetary model in diagrams that summarize the numbers and positions of all three subatomic particles in an atom. In a Bohr-Rutherford(B-R) diagram: the circle in the centre represents the nucleus of the atom the number of protons and neutrons are written in the circle electrons are shown in circular orbits about the nucleus February 10, 2013 2DCHEM - 10 Bohr-Rutherford Diagrams PRACTICE 3. Draw B-R diagrams for each of the elements below. 1 16 (a) H (b) (c) Beryllium (d) Neon 1 8O February 10, 2013 2DCHEM - 11 4
INSTRUCTIONS A. Look at the B-R diagrams and describe: (a) the trends (2) in electron arrangements within a period, and (b) the trends (3) in the electron arrangements within a group. February 10, 2013 2DCHEM - 12 TRENDSINAPERIOD(i.e.arow) Î The number of orbits (or shells) is given by the period. February 10, 2013 2DCHEM - 13 TRENDSINAPERIOD(i.e.arow) Ï The number of electrons in the outermost orbit increases by one as you read from left to right. February 10, 2013 2DCHEM - 14 5
TRENDSINAGROUP(i.e.acolumn) Î The maximum number of electrons in the first orbit is two. The maximumnumber of electrons in the next two orbits is eight. February 10, 2013 2DCHEM - 15 TRENDSINAGROUP(i.e.acolumn) Ï All atoms of elements in the same group have the same number of valence electrons (i.e. electrons in the outermost orbit). For example, all elements in group 1 have one valence electron, all elements in group 2 have two valence electrons, February 10, 2013 2DCHEM - 16 TRENDSINAGROUP(i.e.acolumn) Ð All elements in the noble gas family (i.e. group 18) have completely full valence shells. In other words, the outermost orbit of atoms in this group has the maximum number of electrons. As a result, atoms of elements in this family are extremely unreactive (or stable). February 10, 2013 2DCHEM - 17 6
Trends in Electron Arrangements TRENDS IN ELECTRON ARRANGEMENT # orbits = period # # e s increases as you read from left to right # e s in outermost orbit (i.e. valence electrons) = group # (last digit) February 10, 2013 2DCHEM - 18 7