Atoms are one of the smallest particles of matter
All creatures and things around us are made up of substances and mixtures. Examples of substances include water, sugar, salt, and iron. Each substance has its own characteristics that allow it to be recognised and distinguished from others. All substances consist of small particles. Those particles are called atoms, and they are unimaginably small. Different or similar atoms can form molecules. A molecule is a particle of at least two atoms.
– smallest particle in a substance
– a particle that is made of at least 2 atoms
– collection of similar molecules
– combination of 2 or more substances
Bonus: How many chemical elements are there on Earth?
Some substances are made of only one type of atoms - these substances are called elements. There are 98 natural elements on earth (such as iron, oxygen, copper, gold, carbon, and nitrogen).
- Coal
- Graphite
- Gold
- Diamond
What elements make up water?
A water molecule is made of the atoms of two elements, hydrogen and oxygen. One oxygen atom is bound to two hydrogen atoms in a water molecule. That's why it is written as H2O (read as: aitch-two-oh). The + and - marks on the atoms also have a meaning: particles with the same sign push each other away, while the ones with an opposite sign pull each other like the different poles of a magnet. Similarly, water molecules are attracted to their closest neighbours. Watch the water flowing from the tap! All particles are in a continuous line next to each other.
Properties of Water
The structure of water molecules gives water exactly the properties by which we recognise it. We can easily recognise substances by colour, smell, and taste. For example, clean water is transparent, colourless, odourless and tasteless. Natural water is not a pure substance; it contains the particles of many other substances in addition to water molecules.
Think!
- What words can you use to describe tap water, sea water, river water, and lake water?
Water is a good solvent
There is a lot of salt in seawater, but you can't see it. The salt is there, in a dissolved form, so seawater is a salt solution. A solution consists of a solute (such as salts) and a solvent (such as water). In everyday life, we dissolve substances in water quite often. For example, we add salt to the soup, dissolve the washing powder in water while doing the laundry, and mix sugar into tea.
The liquid in which another substance is dissolved is a. In vinegar,is the solvent andis the solute. Lemonade has bubbles because it has dissolvedin it.
Natural water is always a solution
There are always some dissolved substances, such as salts, in natural water, bottled water, and tap water. Gases such as oxygen and carbon dioxide are also soluble in water. There is always dissolved oxygen in natural water.
Fish need oxygen to live. How do they get it?
- They go to the surface to breathe.
- They breathe the oxygen dissolved in water with gills.
Why is it necessary to put a pump in the aquarium?
- To get enough oxygen into the water.
- To make it interesting for fish to swim through bubbles.
Think!
- Why is seawater salty? Search the internet or books for how salts got into the sea.
Not all substances are soluble in water
Although water is a good solvent, some substances do not dissolve in water, they are insoluble in water. Substances whose particles bind strongly to water molecules are highly soluble in water. Substances whose particles do not affect water molecules have little or no solubility in water. For example, sand, stones, metals, as well as oils and fats are insoluble in water. You need to know this, for example, if you want to remove a grease stain from your clothes. The grease stain cannot be removed from the cloth with water, but gasoline, for example, dissolves the grease.
Bonus: How does oxygen get into the water?
Oxygen enters the water from the air. The larger the contact area between water and air, the more oxygen dissolves in the water. Foaming waves, raindrops falling through the air and falling waterfalls increase the oxygen dissolved in the water. Aquatic plants also add oxygen to the water.
- Sand
- Sugar
- Stones
- Oil
- Oxygen
- Carbon dioxide
- Salt
- Grease
- Washing powder
- Metal
Important terms
- substance – a collection of identical molecules
- molecule – a particle that is made of at least 2 atoms
- atom – the smallest particle of a substance
- solution – a liquid consisting of a solvent and a solute
- solvent – a liquid that dissolves the solute
- solute – a substance that dissolves in the solvent
I now know that…
All living beings and inanimate things around us are made up of substances and their mixtures. Particles, such as molecules, are formed when atoms join together. The water molecule consists of two hydrogen atoms and one oxygen atom. Natural water also contains other substances that are dissolved in water.
