The Periodic Table 2 Lesson 10 October 15th, 2010

Periods and Chemical Families The periodic table has seven horizontal rows. Each of these rows is called a period. A number written on the left side of the table identifies each period. Example: hydrogen and helium are in Period 1. Potassium is in Period 4

There are 18 vertical columns in the periodic table, and each represents a different group (also called a chemical family). The elements within a group share certain physical and chemical properties. Each group has its own number, written at the top of the periodic table. Example carbon (C) is in Group 14.

Properties within Groups Alkali Metals (Group 1): Li, Na, K, Rb, Cs Similarities - All of these metals are silver-grey in colour - conduct electricity and heat - Low MP for metals - Can be cut with a knife - React with air and water

Alkali Metals (Group 1): Li, Na, K, Rb, Cs Differences - Gradual change in physical properties, density increases going down the group. - The elements become softer and MP decreases when moving down the table

Alkali Metals (Group 1): Li, Na, K, Rb, Cs

Alkaline earth metals (Group 2): Be, Mg, Ca, Sr, Ba, Ra They are light, very reactive, solids at room temperature and all react with oxygen in the air.

Transition Metals (Groups 3-12): These metals have a wide variety of properties and reactivates. They are generally hard, strong metals that conduct electricity

Representative Metals(Groups 1,2, and 13-17) Contains metals, non-metals, and metalloids Contains solids, gases and a liquid. These elements follow periodic law.

Halogens (Group 17): F, Cl, Br, I Similarities - All Non-metals - Each has a noticeable colour - all are gasses or easily form gases when heated - All are very reactive - Cl, Br, and I are used as disinfectants

Halogens (Group 17): F, Cl, Br, I Differences - Colours become more intense moving down the group. - MP increases moving down the group. Ended here

Noble Gases (Group 18): He, Ne, Ar, Kr, Xe, Rn Similarities - All are gases that glow with bright colours when current is passed through them (neon light ) - None of the gases are chemically active except in special situations.

Noble Gases (Group 18): He, Ne, Ar, Kr, Xe, Rn Differences - Density increases moving down the group - Balloons filled with the gases will rise or sink at different rates depending on their density.

Chlorine: A Typical Atom Atoms of all elements have the same basic structure but different numbers of protons, neutrons, and electrons. The element chlorine is used as a disinfectant in swimming pools and to purify drinking water. A diagram of an atom of chlorine is shown below. Notice that the number of protons and the number of electrons are equal. This is true of all atoms.

Example: Chlorine atom All chlorine atoms have 17 protons. Each proton has a charge of 1+, so the total positive charge in the nucleus is therefore 17+. Different kinds of chlorine atoms can have different numbers of neutrons. It is the number of protons in an atom that determines what element the atom is, not the number of neutrons. The most common types of chlorine atoms have 18, 19, or 20 neutrons.

The Nucleus The nucleus is a tiny part of the atom that contains protons and neutrons gathered together into a ball. The nucleus contains only a small part of an atom’s total volume. Depending on the atom, the region outside the nucleus of an atom is 10 000 to 50 000 times the diameter of the nucleus.

The Nucleus The nucleus contains 99.99% of the mass of the atom because protons and neutrons have much greater mass than electrons

Electrons Electrons exist in shells, or energy levels, surrounding the nucleus. The innermost shell can hold a maximum of two electrons. Each of the next two shells can hold up to eight. Electrons often exist in pairs in the shells. Electrons occupy more than 99.99% of an atom’s volume.

Electrons Electrons can move between energy levels. The outermost shell that has electrons in it is called the valence shell. Electrons in this shell are called valence electrons. Other shells containing electrons are called inner shells, and the electrons in them are called inner electrons.

Electrons The properties of elements are strongly affected by their valence electrons. When a shell becomes more than half-filled, the electrons begin to pair up, as shown in Bohr diagrams. Even though the negatively charged electrons repel each other, pairing helps electrons to get closer to the positive protons in the nucleus.

Periodic Table Work 1. Find the element boron (B) and shade it in. Then, with the same colour, shade in all elements that make a diagonal below and to the right of boron, starting with silicon (Si). Finally, shade in germanium (Ge), antimony (Sb), and polonium (Po). These elements are the metalloids. 2. All the elements to the left of the metalloids, except hydrogen, are metals. All the elements to the right of the metalloids are non-metals. Label the metals and non-metals, but do not shade them. 3. All the elements in the farthest left column, except hydrogen, react violently with water. Shade them the same colour, and label them “alkali metals.” 4. All the elements in the column to the right of the alkali metals are slightly less reactive than the alkali metals. Shade them another colour, and label them “alkaline earth metals.” 5. Find column 17, and shade all the elements in it the same colour. Label the column “halogens.” Find column 18, and shade those elements their own colour. Label them “noble gases.” 6. Why does it make sense to colour columns rather than rows?

Questions – Hand in for homework check 1. Give the names and symbols for the elements found at these locations in the periodic table. (a) Period 3, Group 1 (b) Period 2, Group 13 (c) Period 4, Group 11 (d) Period 5, Group 17 2. Give the period and group for each of the following elements.(a) Mg (b) Si (c) Cl (d) He (e) Au (f) Pb 3. Compare and contrast the physical properties of different alkali metals. 4. Compare and contrast the chemical and physical properties of the halogens and the noble gases.