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Chemistry Wonder World – Atomic Structure, Electron Shells & Chemical Bonds
© Donald Reinhardt, Sept 22, 2013
The lightest element is hydrogen (H, atomic weight of 1) and one of the heaviest elements of the 92 natural elements is uranium (U, atomic weight 235). Here see and understand the basic structure and function of atoms, their unique properties and the kinds of bonds and compounds that are possible in the wonder world of chemistry.
 Hydrogen Atom with 1 proton and 1 electron shown in a Bohr Model. Photo Credit: Wikimedia Commons
What is an atom?

An atom is the smallest part of any element that has or retains the property of that element.

The atom is the basic unit form of elements. Elements are the fundamental types of all known matter (see the periodic Table of Elements).
There are 92 naturally-occurring elements and about 20 man-made elements for a total of 112 known elements.

Hydrogen, carbon, oxygen, nitrogen, phosphorous and sulfur are 6 different and very common natural elements.

Remember: All elements are composed of atoms.

Each atom of each element has exactly the same, unique properties of that particular element. Atoms of the same element have the same properties and elements that are different have different properties, i.e., different characteristics.

What is the structure of an atom?

An atom has a nucleus in the center of the atom and one or more electrons which speed constantly and rapidly around the nucleus of that atom.

The nucleus always contains one or more protons.

 Except for the most common form of hydrogen, which has no neutrons, every other element has one or more neutrons in the nucleus.

The electrons always move rapidly outside the nuclear area and these orbits are termed electron shells.

What holds atoms together?

The atom is held together by specific nuclear and electronic forces.

Special nuclear forces bind the protons and the neutrons together in the nucleus.

 Outside of the nucleus the speeding electrons are kept in place and attracted by the strong pull and force of the protons
Remember: Electrons are negatively charged and are attracted to protons. 
This also is a universal scientific fact: opposite charges attract, like charges repel. It is interesting that although protons are positively charged they do not repel themselves out of the nucleus as one might expect based on like charges repeling. Therefore, the atomic nucleus with its protons and neutrons is  stable. 

Can the atom be broken, split, subdivided, fractured or added to?

Yes, it can. However, normally atoms have great constancy and resilience and the atom remains intact and unchanged. For example, hydrogen stays as hydrogen and helium as helium. 

A nuclear reaction or nuclear explosion is an example of a major change in the nuclei of atoms.  This change occurs when the atom’s nucleus is either split (fission reaction) or added to (fusion). Whenever either of these events occurs there is a change in the elements involved and there is also a great release of heat and light energies.
Remember, there are two types of nuclear reactions: fusion and fission nuclear reactions. We will discuss these reactions in another chemistry module.
Radioactive isotopes of elements emit nuclear particles and decay over time. Radioactive elements can change into other different elements.

In the simplest cases of atomic changes, electrons may be donated or added to the outermost electron shell of an atom. Whenever this addition or subtraction of an electron occurs the atom becomes a charged atom or ion.

If one or more electrons are added, then the atom becomes negatively-charged. That ion is termed an anion because it will be attracted to an anode which bears a positive charge.

In contrast to this, positively-charged ions or cations form when there is a loss of electrons. The charge of the atom becomes positive because there are more protons in the nucleus than electrons in the shells around the nucleus.

What is a chemical bond?

A chemical bond is the union of two or more atoms to form a compound or a molecule which is the smallest, basic form of a compound. Water (H2O) and hydrogen sulfide (H2S) are two different compounds. In each case, two hydrogens are united to oxygen and sulfur respectively in each compound. Each compound is different and has unique and special properties.

What types of chemical bonds have been discovered?

There are three major types of chemical bonds: ionic (electrovalent), covalent (shared electrons) and hydrogen bonds.

Ionic (electrovalent) bond – electrons lost or gained from atoms cause  ions (charged atoms) to form which interact  in specific and naturally-influenced ways to unite and form compounds with other ions of various elements.  

Key words to remember: charged atoms and attraction and union of opposite charges.

Ionic Bond Strength: Moderate.

This ionic bonding video is excellent and is cited and referenced at the end of this learning module.

Covalent bond – shared electrons from each of two or more atoms promotes and causes union between or among atoms in a compound.

Examples: methane (CH4), CO2, (carbon dioxide), carbon monoxide (CO), water (H2O)

Covalent bonds are typical with carbon compounds and the organic and biochemical compounds of so many different kinds.

Covalent Bond Strength: Moderate to Strong

This video on water explains well the covalent bonding of water as well as how water’s properties include hydrogen bonding and the unique properties of water related to cohesion, adhesion and solvency. Another video on carbon dioxide also explains covalent bonds and the additional concept of the octet rule.

Hydrogen Bond – is the attraction of the proton in the hydrogen atom for the electronegative region of various atoms nearby to that hydrogen.

Example: Water to water intermolecular attractions with frequent breakage and reunion of the weak hydrogen bonds. Hydrogen bonding is very significant and important in the double helix of DNA. Review the video on water under covalent bonding to see hydrogen bonding in action.

What is the Octet (8) Rule of 8 electrons in chemistry?

The Octet Rule states that atoms in chemical reactions and compounds arrange and share  electrons to form a configuration of 8  in the outermost shell of each atom. Therefore, although neither atom alone has by itself the full eight electrons, the sharing 8 pattern of electrons  satisfies and complements in such a way as to function as a full eight electrons for each atom.

How can an atom be diagrammed and sketched to make sense of its nature and character?

There are various models and forms of the atom that have been used to show and explain the atom in simple terms. Two models are shown below: the planetary model and the model. In reviewing these models note that number of protons is the atomic number in the periodic table and the number of protons and the number of electrons are always equal in any element that is not ionized.
Planetary model of a Nitrogen atom with 7 protons and 7 electrons. Photo Credit. Jackson Laboratory. US Dept of Energy
The Bohr Model of a Nitrogen atom with 7 protons and an inner 2 electrons and an outer 5 electrons = 7 electrons. Photo Credit: Jackson Laboratory, US Dept of Energy

Sources, Resources and Credits

National Science Foundation & NBC Learn. How Atoms Bond: Ionic Bonds. Accessed September 21, 2013.

National Science Foundation & NBC Learn. Water: H2O Molecules Made Clear. Accessed September 21, 2013.

National Science Foundation & NBC Learn. The Chemistry of CO2: Carbon Dioxide. Accessed September 21, 2013.