- Define and explain Trends in Groups in your own words
- Use key terms such as group accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Trends in Groups: predict how reactivity changes down Group 1 and Group 7.
Predict how reactivity changes down Group 1 and Group 7.
Key ideas
Reactivity follows trends down a group
In Group 1, reactivity increases down the group: potassium fizzes more violently with water than sodium, which is more vigorous than lithium. This is because the outer electron is further from the nucleus and more shielded, so it is lost more easily. In Group 7 the trend reverses — fluorine is the most reactive halogen — because gaining an electron gets harder as the atom gets bigger.
Position predicts electron arrangement
Elements are arranged in order of increasing atomic number, and this order creates the pattern of groups and periods. The group number tells you the number of outer-shell electrons (for the main groups), and the period number tells you the number of shells. That is why all Group 1 elements have one outer electron and react in similar ways.
Key term — group: A vertical column of the periodic table; elements in the same group have similar properties.
Lithium, sodium and potassium are dropped into water. Put them in order of vigour of reaction, least vigorous first.
Lithium, then sodium, then potassium — reactivity increases down Group 1.
Answer: Lithium, then sodium, then potassium — reactivity increases down Group 1.
- Assuming all metals behave identically Reactivity varies hugely: potassium reacts violently with water while copper does not react at all. Position in the table gives trends, but the trend itself is what you must learn.
- Reading the group number as the total electrons The group number gives the number of outer-shell electrons, not the total. Chlorine in Group 7 has 7 outer electrons, but 17 electrons in total.
Practice
Less reactive: its outer shell is further from the nucleus, so it gains an electron less easily.
2,7.
Both are in Group 1, so both have one electron in their outer shell, which they lose in similar reactions.
The pattern of properties showed that undiscovered elements must exist to fill the gaps, so he left spaces and even predicted their properties.
Quick check
Which of these best defines "group"?
An element is dull, brittle and does not conduct electricity. Is it a metal or a non-metal? Where does it sit in the table?
- Trends in Groups: predict how reactivity changes down Group 1 and Group 7.
- Reactivity follows trends down a group: In Group 1, reactivity increases down the group: potassium fizzes more violently with water than sodium, which is more vigorous than lithium.
- period: A horizontal row of the periodic table; the period number equals the number of electron shells.
- Watch out for: assuming all metals behave identically