4.1
Classification of the elements in s, p and d blocks
ASSIGNMENT 2: PREDICTING PROPERTIES OF AN UNSTABLE ELEMENT (PS 1.1, 1.2, 2.3)
Questions
The element astatine, At, comes after iodine in Group 7(17). When Mendeleev compiled his first Periodic Table, he left a space below iodine and called the element eka-iodine. This was later identified as astatine. The Guinness Book of Records has dubbed astatine as the rarest element on Earth – at any one time there is about 25 g, less than a teaspoonful, on Earth. The Italian physicist Emilio Segrè and his team first produced it in the laboratory at the University of California in 1940. They bombarded bismuth with helium ions, He2+ (also called alpha particles), to produce this new element with atomic number 85. No more than 0.50 µg or 5.0 × 10−7 g has ever been made.
Use the data given in Table A1 to answer these questions.
Its longest lived isotope has a half-life of only 8.3 hours, which means that half the astatine in a sample decays in 8.3 hours. It was named astatine, from the Greek word for ‘unstable’, because of this short half-life. The amount on Earth stays constant because it is formed when some heavier radioactive elements decay.
A5. List the scientific ideas used to make predictions about astatine’s physical and chemical properties.
A1. In which block of the Periodic Table is astatine? A2. Give the outermost sub-shell electron structure of astatine. A3. Predict the following values for astatine: a. density as a liquid
b. melting point
c. first ionisation energy.
A4. Give the formulae of the compounds:
a. sodium astatide
b. hydrogen astatide.
Stretch and challenge A6. Explain why bombarding bismuth atoms with He2+ ions could, theoretically, produce astatine.
Fluorine
Chlorine
Bromine
Iodine
Relative atomic mass
19
35.5
79.9
127
Density as a liquid/g cm−3
1.11
1.56
2.93
4.93
Melting point/°C
−220
−101
−7.2
113.5
Appearance at room temperature
colourless gas
green gas
orange liquid
purple solid
Formula of hydrogen halide
HF
HCl
HBr
HI
1680
1260
1140
1010
First ionisation energy/kJ
mol−1
Table A1 Properties of Group 7(17) elements
KEY IDEAS
›› Elements in the Periodic Table are arranged in
›› Elements are classified as s, p, d or f block
›› The Periodic Table is divided into s, p, d and f blocks. ›› Rows of elements in the Periodic Table are called
›› The Periodic Table can be used to deduce the
order of increasing atomic (or proton) number.
periods and columns are called groups.
elements according to the electron configuration of their outer shells. electron configuration of any element.
93
90216_P089_101.indd 93
02/06/15 8:25 PM