Solids, Liquids, and Gases

We learned in some of our other lessons that matter is made up of atoms and molecules. Millions and millions of these tiny objects fit together to form larger things like animals and planets and cars. Matter includes the water we drink, the air we breathe, and the chair we are sitting on. 

States or Phases 

Matter usually exists in one of three states or phases: solid, liquid, or gas. The chair you are sitting on is a solid, the water you drink is liquid, and the air you breathe is a gas. 

Changing State 

The atoms and molecules don't change, but the way they move about does. Water, for example, is always made up of two hydrogen atoms and one oxygen atom. However, it can take the state of liquid, solid (ice), and gas (steam). Matter changes state when more energy gets added to it. Energy is often added in the form of heat or pressure. 

Water 

Solid water is called ice. This is water with the lowest energy and temperature. When solid, the molecules in water are held tightly together and don't move easily. 

Liquid water is just called water. As ice heats up it will change phases to liquid water. Liquid molecules are looser and can move about easily. 

Gas water is called steam or vapor. When water boils it will turn to vapor. These molecules are hotter, looser, and moving faster than the liquid molecules. They are more spread apart and can be compressed or squished.

The three states of Water

More States 

There are actually two more states or phases that matter can take, but we don't see them much in our everyday life.

One is called plasma. Plasma occurs at very high temperatures and can be found in stars and lightning bolts. Plasma is like gas, but the molecules have lost some electrons and become ions. 

Another state has the fancy name Bose-Einstein condensates. This state can occur at super low temperatures. 

Fun Facts about Solids, Liquids, Gases

• Gases are often invisible and assume the shape and volume of their container.
• The air we breathe is made up of different gases, but it is mostly nitrogen and oxygen.
• We can see through some solids like glass.
• When liquid gasoline is burned in a car, it turns into various gases which go into the air from the exhaust pipe.
• Fire is a mixture of hot gases.
• Plasma is by far the most abundant state of matter in the universe because stars are mostly plasma.

Isotopes

Chemistry for Kids

Isotopes

About Atoms and Elements 

We learned in the atoms and elements sections that each element has its own unique atom which is made up of a specific number of protons. The number of protons determines the atomic number of the element. Each atom also has the same number of electrons as protons. 

What is an isotope? 

Isotopes are atoms that have the same number of protons and electrons, but a different number of neutrons. Changing the number of neutrons in an atom does not change the element. Atoms of elements with different numbers of neutrons are called "isotopes" of that element. 

Naming Isotopes 

Since neutrons have no electrical charge, changing the number of neutrons does not affect the chemistry of the element. It does, however, change the mass of the element. Isotopes are identified by their mass, which is the total number of protons and neutrons. 

There are two ways that isotopes are generally written. They both use the mass of the atom where mass = (number of protons) + (number of neutrons). The first way is to put the mass as a superscript before the symbol of the element:

• ⁴He
• ¹⁴C
• ²³⁵U

The other way is to write out the element and write the mass after a dash next to the element's name:

• helium-4
• carbon-14
• uranium-238

Hydrogen 

Hydrogen is the only element where the isotopes are given specific names. Common hydrogen, which has zero neutrons, is called protium. Hydrogen with one neutron is called deuterium and hydrogen with two neutrons is called tritium. See the picture at the top of the page. 

How many isotopes can an element have? 

All elements have a number of isotopes. Hydrogen has the fewest number of isotopes with only three. The elements with the most isotopes are cesium and xenon with 36 known isotopes. 

Stable and Unstable Isotopes 

Some isotopes are stable and some are unstable. When an isotope is unstable it will decay over time and eventually it will turn into another isotope or element. Unstable isotopes are considered radioactive. Most elements that are found in nature are made up of stable isotopes. The element with the most stable isotopes is tin which has ten different stable isotopes. 

Interesting Facts about Isotopes

• Many elements only exist in an unstable or radioactive form.
• All non-natural or man-made elements are radioactive isotopes.
• Heavier isotopes tend to react more slowly than lighter isotopes of the same element.
• Deuterium (the hydrogen isotope with one neutron) can form water with oxygen. This is called "heavy water" as deuterium has twice the mass of normal hydrogen (protium).
• There are 254 known stable isotopes and 80 elements which have at least one stable isotope.
• Twenty-six elements only have one stable isotope. These elements are called monoisotopic.

Molecules

                                             Molecules

Any time two atoms join together, they make a molecule. All the stuff around you is made up of molecules. This includes you! You are actually made up of trillions and trillions of different types of molecules. 

Compounds 

When atoms of different types of elements join together, they make molecules called compounds. Water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. This is why it's called H₂O. Water will always have 2 times the number of hydrogen atoms as oxygen atoms. 

Water Molecule showing 1 Oxygen atom and 2 hydrogen atoms

Molecular Formula 

There are only just over 100 types of atoms, but there are millions and millions of different types of substances out there. This is because they are all made up of different types of molecules. Molecules are not only made up of different types of atoms but also different ratios. Like in the water example above, a water molecule has 2 hydrogen atoms and 1 oxygen atom. This is written as H₂O. 

Other examples are carbon dioxide (C0₂), sodium chloride (NaCl), and sugar or glucose (C₆H₁₂O₆). Some formulas can get quite long and complex. 

Let's look at the molecule for sugar: 

C₆ - 6 carbon atoms
H₁₂ - 12 hydrogen atoms
O₆ - 6 oxygen atom 

It takes these specific atoms in these specific numbers to make up a sugar molecule.

3D Molecule

Bonds 

Molecules and compounds are held together by forces called chemical bonds. There are two main types of bonds that hold most compounds together: covalent bonds and ionic bonds. Some compounds can have both types of bonds. 

Both main types of bonds involve electrons. Electrons orbit atoms in shells. They want these shells to be full. When they aren't they will try to bond with other atoms to try and fill their shells. 

Covalent Bonds - Covalent bonds share electrons between atoms. This happens when it works out for atoms to share their electrons in order to fill their outer shells.

Ionic Bonds - Ionic bonds form when one electron is donated to another. This happens when one atom gives up an electron to another in order to form a balance and, therefore, a molecule or compound. 

Fun Facts about Molecules

• Oxygen gas normally is the molecule O₂, but it can also be O₃ which we call ozone.
• 66% of the mass of the human body is made up of oxygen atoms.
• Molecules can have different shapes. Some are long spirals while others may be pyramid shaped.
• Organic compounds are compounds that contain carbon.
• A perfect diamond is a single molecule made of carbon atoms.
• DNA is a super long molecule that has information uniquely describing every human being.

THE ATOM

The atom is the basic building block for all matter in the universe. Atoms are extremely small and are made up of a few even smaller particles. The basic particles that make up an atom are electrons, protons, and neutrons. Atoms fit together with other atoms to make up matter. It takes a lot of atoms to make up anything. There are so many atoms in a single human body we won't even try to write the number here. Suffice it to say that the number is trillions and trillions (and then some more). 

There are different kinds of atoms based on the number of electrons, protons, and neutrons each atom contains. Each different kind of atom makes up an element. There are 92 natural elements and up to 118 when you count in man-made elements. 

Atoms last a long time, in most cases forever. They can change and undergo chemical reactions, sharing electrons with other atoms. But the nucleus is very hard to split, meaning most atoms are around for a long time. 

Structure of the Atom 

At the center of the atom is the nucleus. The nucleus is made up of the protons and neutrons. The electrons spin in orbits around the outside of the nucleus. 

The Proton 

The proton is a positively charged particle that is located at the center of the atom in the nucleus. The hydrogenatom is unique in that it only has a single proton and no neutron in its nucleus. 

The Electron 

The electron is a negatively charged particle that spins around the outside of the nucleus. Electrons spin so fast around the nucleus, scientists can never be 100% sure where they are located, but scientists can make estimates of where electrons should be. If there are the same number of electrons and protons in an atom, then the atom is said to have a neutral charge. 

Electrons are attracted to the nucleus by the positive charge of the protons. Electrons are much smaller than neutrons and protons. About 1800 times smaller! 

The Neutron 

The neutron doesn't have any charge. The number of neutrons affects the mass and the radioactivity of the atom. 

Other (even smaller!) particles

• Quark - The quark is a really small particle that makes up neutrons and protons. Quarks are nearly impossible to detect and it's only recently that scientists figured out they existed. They were discovered in 1964 by Murray Gell-Mann. There are 6 types of quarks: up, down, top, bottom, charm, and strange.
• Neutrino - Neutrinos are formed by nuclear reactions. They are like electrons without any charge and are usually travelling at the speed of light. Trillions and trillions of neutrinos are emitted by the sun every second. Neutrinos pass right through most solids including humans!