Atoms

For the past few weeks, we have been studying about atoms. We studied about how atoms were first discovered, then we studied about what an atom is made of, finally we learnt about atoms bond together to create compounds.

History of Atoms

2500 years ago - Democritus said that matter is made up of tiny invisible particles called atoms.

1803 - Dalton's Theory: Atoms of same elements are alike, for example mass is the same, different elements have different types of atoms, atoms cannot be created, destroyed or changed and compounds are of two or more elements combined. Dalton's Theory forms the foundation of modern chemistry.

1877 - JJ Thomson's Model: Electrons are distributed among a mass of positive charges. JJ Thomson found out that an atom is a continuous mass of positive charges containing negative charges called electrons.

1911 - Rutherford's Model: Electrons are orbiting around a small, dense positively charged nucleus.

1915 - Bohr's Model: Electrons move around in a fixed orbit. An atom has a small and dense nucleus made up of of positively charged protons and electrically neutral neutrons. The negatively charged electrons move around the nucleus in fixed orbits. Only a certain number of electrons can be found in each shell.

1926 - Quantum Model: Electrons move around randomly and not in fixed orbits.

What are atoms made of?

Atoms are basically made up of electrons, protons and neutrons.

Electrons are negatively charged and they are the smallest of the three. They move around the nucleus, made up of protons and neutrons, in a random order. Electrons are found in "shells", each shell only able to hold a specific number of electrons. In the first shell, which is the shell nearest to the nucleus, it can only hold up to 2 electrons, while the second and third shell can hold 8. After the 40th element, the third shell can hold up till 18 electrons. The outermost shell is called the valence shell and the electrons inside it are called valence electrons. Only the valence electrons are used during bondings.

Protons are positively charged and they are found in the nucleus. There are the same number of protons as electrons, thus an atom is always electrically neutral.

Neutrons are also found in the nucleus. They have no charge.

Every atom has a mass number and a proton number. Mass number can also be said as nucleon number and proton number can also be said as atomic number. Mass number is the sum of the number of protons and neutrons while proton number is the total number of protons the atom has. These two information would be sufficient to find out all the numbers of electrons, protons and neutrons the atom has. For example, an oxygen atom has a mass number of 16 and proton number of 8. To find the number of neutrons, 16-8=8, thus we can tell that oxygen atom has 8 neutrons. The number of protons is already given and as the number of electrons are the same as the number of protons, oxygen has 8 protons and 8 electrons.

I also found out an easy way to remember the two phrases. As neutrons and protons are the heavier of the three parts, the mass is greatly influenced by the number of neutrons and protons. Thus, the mass number is the number of neutrons and protons. The proton number is also easy to remember because the name already tells me what it is referring to.

Even though atoms are quite confusing at first, I soon found out that it wasn't so hard to remember everything.