Classification Of Matter

ATOMS

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 hydrogen atom 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. 

ELEMENTS

An element is a pure substance that is made from a single type of atom. Elements are the building blocks for all the rest of the matter in the world. Examples of elements include iron, oxygen, hydrogen, gold, and helium.

            Atomic Number

An important number in an element is the atomic number. This is the number of protons in each atom. Each element has a unique atomic number. Hydrogen is the first element and has one proton, so it has an atomic number of 1. Gold has 79 protons in each atom and has an atomic number of 79. Elements in their standard state also have the same number of electrons as protons. 

Silicon (Atomic number 14) is an important element in electronics

Forms of an Element

Even though elements are all made from the same type of atoms, they can still come in different forms. Depending on their temperature they can be solid, liquid, or gas. They can also take different forms depending on how tightly the atoms are packed together. Scientists call these allotropes. One example of this is carbon. Depending on how carbon atoms fit together they can form diamond, coal, or graphite.

How many elements are there?

There are currently 118 known elements. Of these, only 94 are thought to naturally exist on Earth.

 Families of Elements

Elements are sometimes grouped together because they have similar properties. Here a few of the types:

Noble Gases - Helium, neon, argon, krypton, xenon, and radon are all noble gases. They are unique in that the outer shell of their atoms is full of electrons. This means they don't react much with other elements. They are often used in signs as they glow in bright colors when an electrical current is passed through them.

Alkali Metals - These elements have just 1 electron in the outer shell of their atom and are very reactive. Some examples are lithium, sodium, and potassium.

Other groups include transition metals, nonmetals, halogens, alkali earth metals, actinides, and lanthanides.

Periodic Table

An important way of learning and understanding elements for chemistry is the periodic table. You can learn more about this on our periodic table of elements page. 

Fun Facts about Elements

·         Elements found on Earth and Mars are exactly the same.

·         Hydrogen is the most common element found in the universe.

·         It is also the lightest element.

·         Isotopes are atoms of the same element, with different numbers of neutrons.

·         In ancient times the elements referred to fire, earth, water, and air.

·         Helium is the second most common element in the universe, but is very rare on the Earth.

MOLECULES

Molecules are compounds in which the elements are in definite, fixed ratios, as seen in figure below. Those atoms are held together usually by one of the three types of chemical bonds discussed above. For example: water, glucose, ATP. Mixtures are compounds with variable formulas/ratios of their components. For example: soil. Molecular formulas are an expression in the simplest whole-number terms of the composition of a substance. For example, the sugar glucose has 6 Carbons, 12 hydrogens, and 6 oxygens per repeating structural unit. The formula is written C₆H₁₂O₆.

. Determination of molecular weights by addition of the weights of the atoms that make up the molecule.

COMPOUNDS Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white. Note that a compound: consists of atoms of two or more different elements bound together, can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means), has properties that are different from its component elements, and always contains the same ratio of its component atoms.