8.3 Elements
Water looks like one pure thing. But is it the simplest kind of matter, or is it hiding something? Electricity gives the answer.
Activity 8.3 — Splitting water with electricity Fill two test tubes with water (plus a few drops of dilute sulfuric acid) inverted over the terminals of a 9 V battery. After a few minutes, gas bubbles collect in both tubes — and twice as much gas in one as the other. Test them with a flame: one gives a “pop” (hydrogen), the other makes the flame glow brighter (oxygen). The water has been split into two different substances.
\text{Water} \longrightarrow \text{Hydrogen} + \text{Oxygen}
The hydrogen and oxygen we get cannot be broken down any further — they are the simplest substances, called elements.
What Is an Element? An element is a pure substance that cannot be broken down into anything simpler. Each element is made of its own kind of identical particles called atoms (iron is made of iron atoms, gold of gold atoms), different from every other element’s atoms. Elements are the building blocks of all matter. (Often atoms join into molecules — two hydrogen atoms make one hydrogen molecule.)
Metals and non-metals
Two Families of Elements Elements split into metals (gold, silver, iron, aluminium, magnesium) and non-metals (carbon, sulfur, hydrogen, oxygen). A few in-between elements like silicon and boron, with properties of both, are called metalloids.
Sort these elements into metal or non-metal.
A Step Further: Counting the Elements There are 118 known elements, most of them solids. Just eleven are gases at room temperature (all non-metals — oxygen, nitrogen, helium…), and only two are liquids: mercury (a metal) and bromine (a non-metal). Fun fact: more than 45 different elements go into a single mobile phone! (Gallium and caesium are solids that melt in your hand, near 30 °C.)