Atoms and Elements | A+ Tutors Lanka

Principles of Chemistry

1.2 Atoms and Elements

Atoms are the smallest particles of matter. Atoms are made up of smaller components known as sub-atomic particles but as a whole the atom is the furthest point to which we can break down a specific substance.

Empty space

(mostly likely to find electrons)

Nucleus

Dalton's Atom Model

Single atoms are invisible to the naked eye but visible through a microscope. If you were to collect millions of atoms in one place you can start seeing the clusters. When they combine they can form structures that are incredibly strong like diamonds. But the strange thing is that these atoms are mostly empty space. They have a dense center known as the nucleus but surrounding the nucleus is mostly empty space where you can most likely find electrons moving around; its basically a cloud of electrons as illustrated above.

Elements

Now that we know what the atom is and possibly looks like lets discuss about clusters of atoms. If have multiple atoms of the same kind join together to form a cluster, the substance formed is known as an element. In other words an element is a pure substance that is only made from one kind of atom. What do we mean by one kind of atom? This means that all the atoms in the element have the same number of electrons and the same type of nucleus.

There are 90 naturally occurring atoms in nature. Another 28 have been made in labs by scientists. What do you think is different about these naturally occurring elements and the synthesized elements. The synthesized elements are very unstable and break down almost immediately after they are created.

In total there are 118 elements. The cool thing is that some of these elements have similar properties and some properties change in a sort of sequence. This means that we can group them together, which will make studying them easier for us.

Now that we have a basic understanding about atoms and elements let us dig deeper and learn about the nucleus and electrons.

Sub-atomic Particles

The nucleus is the most dense part of the atom. It is made up of two kinds of sub-atomic particles called protons and neutrons. Protons and neutrons together are called nucleons. Even though the nucleus is dense its not exactly heavy; they are incredibly light; therefore, we need a special unit to measure its mass.

Atomic mass units (amu) is a measuring system used to quantify the mass of an atom. (1 amu =0.00000000000000000000000167 g). 1 proton = 1 amu. Whereas 1 electron = 1/ 1836 amu. Since the mass of electrons are incredibly small relative to protons it is taken as zero. Therefore, the nucleus makes up the mass of the atom. The neutron has no charge; each proton has a +ve charge and each electron has a -ve charge. Since the number of protons and electrons in an elemental atom is equal, the +ve charges and - ve charges cancel out to give a neutral atom.

I am sure the above picture is what you think of when you think of an atom. However, in the real atom the electrons don't really move around in fixed circular orbits like that. The Dalton model is the best model. The electrons are most likely to be found moving around at certain energy levels away from the nucleus. These energy levels are known as shells.

The more energy the electron has, the further away it is from the nucleus.

The proton number, also known as the atomic number, is the number of protons in an atom. You can easily use this number to identify the kind of atom it is and which element it belongs to. The nucleon number, also known as the mass number, is the sum of protons and neutrons.

Let's look at an oxygen atom. We use O to represnt oxygen as shown above. The proton number is always shown on the bottom and the nucleon number is shown on the top of the symbol. So in this case the number of protons is 8 therefore the number of electrons is also 8. The number of neutrons = 16 - 8 = 8.

Isotopes

We now know that each element is made up of a one kind of an atom. That should mean that all atoms of that element has the same proton number and mass number. However, that is not always the same. There are some atoms of an atom that want to be slightly different. These atoms of an element are known isotopes. How are they different? They have the same proton number and same number of electrons but they have different number of neutrons. But their chemical properties are unchanged because they have the same number of electrons.

The following are the most stable (natural) isotope forms of oxygen. Oxygen 16 is the most abundant with 99.67%, Oxygen 17 has an abundance of 0.04% and Oxygen 18 has an abundance of 0.02%. Lets calculate the average of of the mass number

16 x 99.67/100 + 17 x 0.04/100 + 18 x 0.02/100 = 15.96 ~ 16

Therefore oxygen 16 is used to represent oxygen.

Most elements have isotopes and they are mostly stable. However, they also have unstable isotopes which break down after they are formed. These isotopes are known as radioactive isotopes or radioisotopes. Oxygen 14 is a radioactive isotope which is why it is not found naturally.

As you may know, radiation is harmful to our bodies. A large dose of radiation can destroy and mutate your cells from the insides. Victims would start vomiting, loosing hair, bleeding, get open sores on skin and eventually die in days. It is very frightening. Fortunately the radioactivity doses in nature are not big enough to harm our health.

If you think about it, radioactivity is actually concentrated amounts of energy. Therefore, there must be uses for it right.

It is used to kill bacteria (sterilization) and cancer cells. It is also used as tracers to map and scan things that not directly visible. For example it can be used to scan your heart to create a map of the blood vessels. It can also be used as a source of X-Rays.