LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- describe the arrangement of the Periodic Table
- connect group and period position to electronic configuration
- explain trends in Group I and Group VII
- describe transition-element properties
- explain noble-gas unreactivity
THE BIG IDEA
Use electron arrangement and periodic position to explain group trends and predict element properties.
The Periodic Table arranges elements by increasing proton number. Repeating outer-electron patterns produce repeating chemical properties.
A trend is more useful when it is explained through atomic structure rather than memorised as a list.
SECTION 01
Arrangement and prediction
Horizontal rows are periods and vertical columns are groups. Across a period, character generally changes from metallic to non-metallic.
For main-group elements, group number shows outer-shell electrons and helps predict ion charge. Period number shows occupied shells.
Elements in one group behave similarly because they have the same number of outer-shell electrons.
KEY IDEAS
- Group I forms +1 ions.
- Group II forms +2 ions.
- Group VI forms −2 ions.
- Group VII forms −1 ions.
SECTION 02
Group I alkali metals
Lithium, sodium and potassium are soft, relatively low-melting metals. Down the group, melting point decreases, density generally increases and reactivity increases.
Each atom loses one outer electron. Down the group this electron is farther from the nucleus and more shielded, so attraction is weaker and electron loss is easier.
Reactions with water form a metal hydroxide and hydrogen and become increasingly vigorous down the group.
SECTION 03
Group VII halogens
Chlorine is a pale yellow-green gas, bromine a red-brown liquid and iodine a grey-black solid at room temperature. Density increases and reactivity decreases down the group.
A halogen atom gains one electron. Down the group, greater distance and shielding weaken attraction for an incoming electron.
A more reactive halogen displaces a less reactive halide from solution.
SECTION 04
Transition elements
Transition elements are dense, high-melting metals. They form coloured compounds and often act as catalysts as elements or compounds.
Their ions can have variable oxidation numbers, such as Fe²⁺ and Fe³⁺.
KEY IDEAS
- Iron catalyses the Haber process.
- Vanadium(V) oxide catalyses the Contact process.
- Transition-metal properties differ from Group I metals.
SECTION 05
Noble gases
Group VIII noble gases are monatomic and very unreactive because their outer electron shells are full.
Their low reactivity makes them useful where an inert atmosphere is needed.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Atomic number orders the Periodic Table.
- Outer electrons explain group chemistry.
- Group I reactivity increases down the group.
- Group VII reactivity decreases down the group.
- Transition elements show coloured compounds, catalysis and variable oxidation numbers.