Week 3 · Lesson 2 The Periodic Table of Elements (A): Mendeleev, Moseley, the modern periodic table, blocks and groups · 3 lessons
3
Blocks and groups: reading the table’s map
Science Prep 1 Term 1, Unit 1: pp. 10–13
GoalRead the map of the periodic table: blocks, special groups and the states of the elements.
New words
block · a region of the table named s, p, d or falkali metals · the elements of group 1A (group 1)halogens · the elements of group 7A, just before the last groupnoble gases · the elements of the last group, group 0
Explanation
The table is a map. On the left is the s block: group 1A, the alkali metals, and group 2A, the alkaline earth metals. (In the 1 to 18 numbering these are groups 1 and 2.) On the right is the p block with six groups, 3A to 7A and 0. Group 7A is the halogens, and group 0, the last one, is the noble gases. In the middle is the d block, the transition elements, which begin in period 4. The f block sits in two rows at the bottom. The first four periods hold 2, 8, 8 and 18 elements. Most elements are solids. Only two are liquid at room temperature: mercury (Hg), a metal, and bromine (Br), a nonmetal. The noble gases (He, Ne, Ar, Kr, Xe, Rn) are gases, and so are H, N, O, F and Cl. Hydrogen stands on the left above group 1A, but it is a nonmetal gas, not an alkali metal.
Worked examples
Where is chlorine (Z = 17)? It is in period 3 and group 7A, in the p block. Group 7A holds the halogens, so chlorine is a halogen, and a gas at room temperature.
The alkali metals Li, Na and K are marked in the table drawn at the start of this lesson. They are all in group 1A, so we expect them to have similar properties. Hydrogen is above them, but it is not an alkali metal.
Solid
Liquid
Gas
Na, Fe, Cu
Hg, Br
H, N, O
C, Al, Si
Ne, Cl
Sorting by state at room temperature. Most elements are solids. Mercury and bromine are the two liquids. Gases include the noble gases and H, N, O, F and Cl.
Class activity
Mystery element. Write four clues on a card about an element from the first 20, for example: “I am in period 3. I am in group 7A. I am a gas.” (Answer: chlorine.) Swap cards with a friend and use the table to solve them. Think about it: do you think the periodic table is finished? Why, or why not?
Practice
1
Which block do the alkali metals belong to?
The s block (group 1A).
2
Name the two elements that are liquid at room temperature.
Mercury (a metal) and bromine (a nonmetal).
3
What are the elements of group 0 called, and what state are they in?
Noble gases; they are gases.
4
Is hydrogen an alkali metal? Explain.
No. It stands above group 1A but it is a nonmetal gas.
