What Is an Atom?

What Is an Atom?

An atom is the basic unit of an element. An atom is a form of matter which may not be further broken down using any chemical means. A typical atom consists of protons, neutrons, and electrons.

Atom Examples

Any element listed on the periodic table consists of specific atoms. Hydrogen, helium, oxygen, and uranium are examples of types of atoms.

What Are Not Atoms?

Some matter is either smaller or larger than an atom. Examples of chemical species that are not typically considered atoms include particles that are components of atoms: protons, neutrons, and electrons. Molecules and compounds consist of atoms but are not themselves atoms.

Examples of molecules and compounds include salt (NaCl), water (H2O), and methanol (CH2OH). Electrically charged atoms are called ions. They are still types of atoms. Monoatomic ions include H+ and O2-. There are also molecular ions, which are not atoms (e.g., ozone, O3-).

The Gray Area Between Atoms and Protons

Would you consider a single unit of hydrogen to be an example of an atom? Keep in mind, most hydrogen "atoms" do not have a proton, neutron, and electron. Given that the number of protons determines the identity of an element, many scientists consider a single proton to be an atom of the element hydrogen.

Structure of the Atom

At the center of the atom is the nucleus. The nucleus is made up of 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.

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 traveling 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!

Chemical composition of the human body

Many of the elements found throughout nature are also found within the body. This is the chemical composition of the average adult human body in terms of elements and also compounds.

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

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), ammonia (NH3), and sugar or glucose (C6H12O6). Some formulas can get quite long and complex.

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.

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.

next lesson...Elements in the periodic table