reactive

Everyday

1. (science) Likely to change quickly when it meets another substance; a reactive metal like sodium reacts strongly with water. tree →
2. Acting only after something has happened, instead of planning ahead (the opposite of "proactive"). tree →
3. Easily upset or quick to respond strongly to things, like a reactive dog that barks at everything. tree →

In the lessons

In science lessons, the reactivity series lists metals from most reactive (potassium, sodium) to least reactive (gold, platinum) — gold stays shiny because it is not reactive. In everyday life, a reactive person or team waits for problems and then fixes them, while a proactive one prevents them. Phrases: highly reactive, reactive metal, reactive to light, reactive rather than proactive.

Examples

• Sodium is so reactive that it fizzes and bursts into flame in water. tree →
• Gold is not very reactive, so it does not rust. tree →
• Our dog is reactive and barks at every bike. tree →
• Don't just be reactive — plan ahead before problems happen. tree →
• Some sunglasses are reactive to light and darken in the sun. tree →
• Potassium is more reactive than iron. tree →

Note

Opposite in science: unreactive or inert. Opposite in behaviour: proactive. Noun: reactivity (science) or reaction. Do not confuse "reactive" (likely to react) with "radioactive" (giving off radiation).